# Kettle Evaporation -



## Thirsty Boy (31/7/10)

Ok, so while merrily arguing with Nick in another thread with evaporation in the title, I have also been having grand chicken cacciatore that my lovely wife made for dinner and annoying her in the kitchen while doing a couple of benchtop experiments on evaporation rates.

Just to be clear though - so as not to make it seem like I am carving off a separate thread in which to continue arguing with Nick in a more concentrated fashion, I have not and don't really intend to cover the particular evaporation topic we have been bickering about about.

What I am interested in is this.

*Can Evaporation Rate be changed by adjusting your boil vigour via increasing or reducing your applied heat??*

One that's always annoyed me. I am often assured that the primary factor in evaporation rate is the diameter and thus surface area of your brew kettle. Boiling harder or softer will either not or only very minimally change the amount that you boil off. I am sure that this is rubbish - its plain to me that if you boil harder, more will boil away. So here's my little test - take it with the grain of salt that I am trying to confirm my pre-conception rather than simply seeking raw data.

Start with 2 x 1L Schott Duran beakers, obviously not identical, but pretty damn similar - filled to the 900ml line. Bring to a hard boil on separate burners of the stove.







Once boiling, turn off heat momentarily and adjust back to the 900ml line with boiling water from the kettle






Bring back to full boil very briefly, then adjust heat down on one burner so the water is boiling actively but "softly" - make the other beaker boil "hard"






Photos are a hard way to judge boil intensity, so here's a video too if you are willing to waste the bandwidth.





Boil for a decent period and compare the amount boiled off. I boiled for about 40mins and here's what came out. Soft boil on the left, hard boil on the right.






And its pretty obvious that I got the result I was expecting. Now its not brewing, its in little beakers on the stove, things would of course be different in a real world situation. But nonetheless, the only significant difference between those two beakers was the intensity of the boil... and the difference in boil off rates was I think you'll agree, quite large.

So I'd conclude from that experiment that while kettle diameter is one of and maybe the most important factor in determining evaporation rates, its certainly possible to at least make an impact on your kettle boil off by adjusting the amount of flame you shove into the bottom of your pot.

Another little experiment on the way shortly

TB

PS - SWMBO will probably kill me if she finds out I posted something to the web that includes a picture of how dirty out stovetop currently is. We did just finish cooking dinner though, and I beat the shit out of that stove with brewing stuff


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## Thirsty Boy (31/7/10)

I'm also interested in this one.

*Does putting a lid on or partially on your kettle change the evaporation rate??*

I discussed this with PP a couple of times. I thought it obvious that this would be true - and think that I find it to be true in my brewery. But PP is dead sure and has done a bit of testing to the effect that it either doesn't or only fractionally changes things. So I thought I'd better test it too while I was bugging the wife.

My contention is that the lid makes the boil more intense for a given flame/heat setting, so you can apply less heat to get the same boil vigour, and the result of both the lid being on and the reduced heat flux, will be that you boil off less liquid in a given time.

So - same as last time. Two beakers, up to the 900ml mark, up to a hard boil, adjusted to 900ml with boiling water.

This time one got a lid - as you can see, it goes over the whole beaker, but there is a nice big spout for steam to escape from, and its pretty obvious that this lid isn't going to be holding in any significant amounts of pressure etc.






Now comes the bit where its nowhere near as quantitative as the last test.... Bring both beakers back to a medium boil. They naturally boil at different intensities because of the lid, but I try to adjust them so that to my eye both are boiling with the same amount of vigour. I have my pre-conceptions about this test... so I ask my wife who doesn't know what its about to check, she makes me adjust the non-lid beaker down a little.






Boil both beakers for the sameperiod, checking periodically to make sure the boil intensities don't drift. 30-40min or so. Compare amounts boiled off. Here's what I got.






Less dramatic than the boil intensity expt.. but still a significant difference. Of course, in this case there is a large element of "judgement" which muddies the waters a chunk. And also... I boiled off 78% of the (unlidded) sample to get that large a difference. No one s boiling off that much of their wort!

What if it was less... well too hard to measure with any accuracy at home, so lets make a wild assumption or two. Say for examples sake that the unlidded volume is 200ml and the lidded volume is 400ml. So that means a 100% difference... but over a 70% total boil off. If the boil off is linear over time/volume (and I have no idea) then that's 50% difference in a 35% boil off & 25% diff in a 17.5% boil off. So those inferences being true (they probably aren't) it'd make really, really roughly 25% _difference_ to have a lid almost completely on your kettle if you were "normally" boiling off 17% or thereabouts of your kettle volume.

Which should suffice to drop a 17% boil off to a 13ish% boil off.

Now I don't for a second pretend that that is going to actually translate directly into what would happen in a full size boil, and it says virtually nothing about what might happen when a lid is covering a lesser proportion of the kettle opening. But it does point to the possibility that covering or partially covering your kettle with a lid can make a small, but noticeable difference to the amount of liquid that boils away in a given pot at similar boil vigour.

That's enough for tonight, if I think of more and get bored enough I'll post em. Feel free to add your experiments too.

TB


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## marksfish (31/7/10)

great job if i had the gear i would try some wort just to see if it made any difference :icon_cheers:


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## clarkey7 (31/7/10)

That's great Thirsty. :icon_cheers: 

I brew outside and notice a huge difference in boil off volumes with windy days.

Building barriers from bricks, kids toys, sandpit covers and BBQ setting chairs helps..  

PB


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## Tyred (31/7/10)

Simple experiments but it shows the point quite well. This is my take on it.

The first example simply shows what should be known by common sense, that the more vigorous boil drives of more liquid. This could be due to the surface tension of the liquid being broken more often allow more vapor to be driven off.

The second example is a little trickier and would probably be due to a couple of factors. It make sense that a lidded boil will loose less liquid as the lid provides a point for condensation and allows for the return of some liquid to the solution. The other factor is that the lid also allows for the increase of humidity in the local area above the liquid making it slightly harder to push the liquid into gaseous form. Pocket Beers noted this when boiling outside on windy days. The wind drives off the vapor off the surface of the liquid allowing for more to be put into the surrounding area. Blocking the wind lessens this effect.


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## Nick JD (1/8/10)

Thirsty Boy said:


> But it does point to the possibility that covering or partially covering your kettle with a lid can make a small, but noticeable difference to the amount of liquid that boils away in a given pot at similar boil vigour.



How do you stop the condensed vapour (containing all the stuff you are boiling to be rid of) from refluxing?


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## Thirsty Boy (1/8/10)

Nick JD said:


> How do you stop the condensed vapour (containing all the stuff you are boiling to be rid of) from refluxing?



You don't particularly.

Reflux off a lid is an issue related to re-introducing unwanted volatiles. That will obviously happen, but they will re-boil and re-evaporate. If you were on the lower limit of the evaporation range and barely getting rid of the required volatiles in the first place, I imagine it would be an issue. But seeing as the reason you would want to put a lid on in the first place would be to reduce your excessive evaporation.... You have a bit of spare capacity in your system for volatile stripping which will take care of it.


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## PistolPatch (1/8/10)

Good on you Thirsty though I am a bit shocked at the state of your stovetop .

You've probably had enough but if you get bored again today, can you try the following please .

Try the difference between a simmer and a gentle boil to see if the difference is less marked than the difference between a gentle boil and a hard boil.

The other one that would be interesting is the second experiment but only using half-filled beakers and 3/4 covering one of them. (Use gentle boil on both.) I suspect the increased headspace and larger opening could make a bit of difference.

Good on you once again for getting the beakers out and taking the time to do the above :super:. 
Pat


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## Thirsty Boy (1/8/10)

I can give the simmer vs gentle boil a go... But only for you Pat  i was reluctant to use a "simmer" as part of the experiment... I wanted to keep it to more brewing like parameters and I wouldn't ever simmer a wort. But as an experiment I guess it would tell us something. What about the difference between two boils that I would consider the low and high extremes of "acceptable" boil vigor?

The second one I don't think I could meaningfully do... Limited by the vessels I have available. Those beakers are the only two almost identical, fairly well graduated containers I have... if I half filled them and went for an experiment that was trying to measure a smaller effect.... I think any difference would get lost in observational error. I'll maybe give it a go, but I don't hold out much hope that anything useful will come out.

Next time I'm bored and there is nothing on the Telly.


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## PistolPatch (1/8/10)

You de man!

Those beakers make for nice illustrations. I'm about to watch a movie so maybe I'll stop being lazy and try the second thing above in a 20 lt pot I've got. Will be a bit inaccurate though as I won't be able to do a side by side. Anyway, I'll have a crack .

Donya,
Pat


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## grod5 (1/8/10)

Only one problem I can see is that the Chef Consul infra-ray had some issues with gas pressure distribution with its two front burners. So the boil vigor (heat intensity) may not be equal. Maybe this experiment should be undertaken by volunteers from AHB to increase the sample size for a better educated opinion.

Sadly, I will be doing my hair that day and cant assist with the research group.

daniel


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## Nick JD (1/8/10)

grod5 said:


> Only one problem I can see is that the Chef Consul infra-ray had some issues with gas pressure distribution with its two front burners.



Daniel! Don't mess with the "science". :lol: Can I even be bother to suggest the same experiment should be repeated with the beakers swapped and then the results averaged? No I can not because this shit ain't ever gonna make it into the Journal of Brewing & Distilling.


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## PistolPatch (1/8/10)

Okay gave 5 boils a go in a pot 23cm high with a diameter of 27.8cm. All boils started with 10cm of water and then boiled for 40 minutes.

*First Three Boils - Simmer versus Boil plus 3/4 Lid Cover*

1. Gentle Boil* with Lid 3/4 On - 7.4 cm remaining after boil so 2.6 cm evaporated.
2. Smallest Simmer Ever with Lid 3/4 On - 8.2 cm remaining after boil so 1.8 cm evaporated.
3. Gentle Boil* with No Lid - 7.3 cm remaining after boil so 2.7cm evaporated.

* This was the hardest boil I could manage to get on my stovetop.

Here's a pic of how much the lid was on and the lid sloped back into the pot...




So, initial conclusions are:...

A. Simmer versus Gentle Boil: A significant difference occurred here although the simmer could hardly be called a simmer as there were only bubbles on the bottom of the pot - none on the top. You certainly wouldn't want to boil like this. However reducing the enrgy source makes an obvious difference to evap rate.

B. Lid 3/4's On: Having the lid 3/4 on on a half-full pot makes very little difference to the evaporation rate (probably because the pressure above the surface is not significantly reduced.) The vigour of the boil did not visibly change if the lid was taken away. Of course, if the lid was fully on, there would be a difference due to increased pressure (like we all know from completely covering a boiling saucepan with a lid.)

*Last Two Boils - Using a Floatie*

Thirsty has suggested floating something on the surface of the wort to decrease evaporation rate and energy required for the boil. In this case I used a saucepan to float inside the pot. The saucepan had a diameter of 19.5 cm and therefore a surface area of 29.9 cm2. The pot had a surface are of 60.7 cm2 and so the effective surface area of the pot was reduced by about 50%. 

4. Floatie with Gentle Boil - 8.4 cm remaining after boil so 1.6cm evaporated.
5. Floatie with Maximum Heat Source* Applied - 7.3 cm remaining after the boil so 2.7 cm evaporated. (This produced a very hard boil).

*In other words, the same heat energy was used as in 1 and 3 above.

The floatie looked like this during Boil 5...




Conclusions from the Floatie are...

C. Floatie can be used to assist achieving a rolling boil in situations where the energy source is weak.
D. Floatie can be used to significantly reduce evaporation rates whilst maintaining a rolling boil.
E. Floatie can be used to significantly reduce energy consumption. (I am estimating that the flame used in 4 above was about 60% of that used in 1, 4 and 5.

So, Thirsty, I am liking your floatie idea a heap and will give it a go on my next single batch though I always seem to do doubles lately.

Spot ya,
Pat


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## Thirsty Boy (2/8/10)

grod5 said:


> Only one problem I can see is that the Chef Consul infra-ray had some issues with gas pressure distribution with its two front burners. So the boil vigor (heat intensity) may not be equal. Maybe this experiment should be undertaken by volunteers from AHB to increase the sample size for a better educated opinion.
> 
> Sadly, I will be doing my hair that day and cant assist with the research group.
> 
> daniel



I actually considered this, and also swapping burners - but neither of the experiments I did requires the applied heat to be the same. The first obviously had different heat intensities... And in the second I deliberately changed the heat settings to get a consistent boil vigor. The flame settings were noticeably different.

So the energy output of the burners was irrelevant to the experiments and the old chef stove was more than sufficient form the job.

Pat - interesting, i'll have to give it a crack now to see what results I get.


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## Wolfy (2/8/10)

Interesting, informative, well done, and amusing.
However, are you not just wasting water, energy (both your own and the gas) and time to prove what is logical and common sense?

Boil harder and get more evaporation losses.
Cover the pot and lose less to evaporation.
Have less surface area and so you have less evaporation losses.

The first idea/concept, I use all the time when cooking and need to 'reduce' the liquid more quickly (usually by that stage I'm getting hungry and want to eat so speed the process up as much as possible).
The second idea/concept is again used all the time when cooking to retain as much liquid as possible (I'd boil dry my potatoes all the time if I didn't put the lid on).
And the last idea/concept is once again often used when cooking, since a large surface frying pan will allow you to 'reduce' the liquid much more easily than the same in a smaller diameter saucepan.

If anyone argues the logical conclusions of your experiment, maybe they should stop arguing about pedantic brewing theories online and get in the kitchen and do some (more) cooking.


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## yardy (2/8/10)

too much time on your hands you blokes h34r:


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## Thirsty Boy (2/8/10)

Wolfy said:


> Interesting, informative, well done, and amusing.
> However, are you not just wasting water, energy (both your own and the gas) and time to prove what is logical and common sense?
> 
> Boil harder and get more evaporation losses.
> ...



I don't think so, I mean I'm still just having a bit of fun, but I'm not so sure that common sense necessarily prevails in all these situations. 

Boil harder - how many times i've had people tell me it won't make any, difference to boil off rate? Enough so i needed to prove it one way or the other.

Cover the pot and lose less - seems logical, seems to work at kitchen level, but Pat has done some work measuring this stuff and was finding that lids partially on made no difference. And really, look at the physics of vaporization and it shouldn't make much difference. but I was sure it would... So a test. my gut feel is thee is going to be a large difference between lid partly on and lid totally on. Plus I think that the difference in surface area to volume ratio in a kitchen sized boil to a brewing sized boil is going to make a difference. My pre-conception is that the lid even partially on will make a noticeable difference, but I still think it's worth a little testing over a beer or two while there's nothing on TV.

Less surface area - once again, I know that reducing it works, and that large surface area make a big difference to boils, boil vigor, energy source you can use etc etc. But surface area really should only matter to evaporation rather than vaporization (I have been ruthlessly misusing the terms which is probably driving any real scientist silly enough to read this thread to distraction) .... But I'm not sure that both aren't at play, so tests with barely simmering vs boiling water might help a little to clear up the picture.

I like to be right.... And if I'm going to talk about this stuff and be arrogant enough to advise other people what I think they should do... I want to be sure what I am saying is true, not just that it makes common sense. I'm also arrogant enough to think that some people will be interested in watching me do it. Besides, playing with fire and boiling water is a lot of fun... Might make mud pies next 

TB


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## Fourstar (2/8/10)

Thirsty Boy said:


> Besides, playing with fire and boiling water is a lot of fun... Might make mud pies next



It sounds like your little experiment was as amusing as watching water boil.


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## Nick JD (2/8/10)

PistolPatch said:


> D. Floatie can be used to significantly reduce evaporation rates whilst maintaining a rolling boil.



I'm gonna say it one last time, _reducing the surface area of the top of a boil by half, and seeing a "rolling boil" in half of the surface doesn't mean you've increased the vigour of the entire boil - _just half of it. The net vigour of the boil is exactly the same as without the floatie.

Ask yourself this question: what kind of boil is happening in the hidden half of the pot? 

Which has always been my point. How this is confounding the intelligent people here is beyond me. What you are thinking of as a rolling boil is actually a gentle boil in entirety - you're only looking at the rolling part.


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## Fourstar (2/8/10)

Nick JD said:


> I'm gonna say it one last time, _reducing the surface area of the top of a boil by half, and seeing a "rolling boil" in half of the surface doesn't mean you've increased the vigour of the entire boil - _just half of it. The net vigour of the boil is exactly the same as without the floatie.
> 
> Ask yourself this question: what kind of boil is happening in the hidden half of the pot?
> 
> Which has always been my point. How this is confounding the intelligent people here is beyond me.




Now im no expert in thermo/fluid dynamics but as you noted, you may not have incrased the 'vigour' (intensity) if the entire boil but by channelling the evaporation via a concentrated point you may have increased the convection/rolling of the boil, right? Isn't that the primary purpose of popping the lid on anyway? To increase the convection? An explosive boil jumping out of the kettle is just as pointless as one that is shimmering.

The only way i could believe this to not be the case is to visually observe it in a glass beaker.

Thirsty, i throw the mantle to you!


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## Nick JD (2/8/10)

Fourstar said:


> Now im no expert in thermo/fluid dynamics but as you noted, you may not have incrased the 'vigour' (intensity) if the entire boil but by channelling the evaporation via a concentrated point you may have increased the convection/rolling of the boil, right? Isn't that the primary purpose of popping the lid on anyway? To increase the convection? An explosive boil jumping out of the kettle is just as pointless as one that is shimmering.
> 
> The only way i could believe this to not be the case is to visually observe it in a glass beaker.
> 
> Thirsty, i throw the mantle to you!



I'd be interested to see that too. I'm quite happy to be proven wrong - and never happy to be guessed wrong. :icon_cheers: 

Will we see though the side of the beaker a strong boil on one side and a simmer on the other?


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## rude (2/8/10)

Thats why I do a 90min boil, the first half hour is a good rolling boil, then for hop additions I tone it down a tad, towards the end partly cover with the lid 

So I figure the volitiles are boiled away at the start


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## raven19 (2/8/10)

TB - Time to step this up to some 5L mini batches of beer for side by side boils, chilling, fermenting, then side by side tastings me thinks!

It would make brewing a simple 20L batch take all day mind you... :icon_cheers: 


Slightly :icon_offtopic: I know I have to watch my kettle like a hawk with the lid on when getting up to the boil to avoid boil overs.

And wind results in heat being stripped from the kettle sides - on our group brew day many of us struggled to get anything more than a simmer.

Back on topic - How about running range hood for one sample and not the other to see if removing steam quickly would result in more evaporation?


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## Thirsty Boy (2/8/10)

Nick JD said:


> I'm gonna say it one last time, _reducing the surface area of the top of a boil by half, and seeing a "rolling boil" in half of the surface doesn't mean you've increased the vigour of the entire boil - _just half of it. The net vigour of the boil is exactly the same as without the floatie.
> 
> Ask yourself this question: what kind of boil is happening in the hidden half of the pot?
> 
> Which has always been my point. How this is confounding the intelligent people here is beyond me. What you are thinking of as a rolling boil is actually a gentle boil in entirety - you're only looking at the rolling part.



It's confusing neither myself nor the other people who have done it... You are simply incorrect. The rate at which the entire volume boils is increased. You may think you should be correct... But you aren't.

And just to try to finally put your mind at ease.... It would not matter one tiny bit if you were correct, because you obviously misunderstand the object of a vigorous boil in terms of brewing. The object is to increase the physical speed with which the wort moves around in the pot.... You can do this by increasing the rate at which the wort boils across the whole pot, you can do it by concentrating the flow of bubbles and wort through a smaller area, you can do it by simply sticking a mechanical agitator into the kettle and a few other ways besides. Perhaps go look up some things like asymmetric boil kettles, external boilers, internal calendria, wort spreaders, pumped boils etc.

Your argument is both incorrect and irrelevant, and who honestly expected anything else?


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## Wolfy (2/8/10)

Thirsty Boy said:


> I like to be right.... And if I'm going to talk about this stuff and be arrogant enough to advise other people what I think they should do... I want to be sure what I am saying is true, not just that it makes common sense. I'm also arrogant enough to think that some people will be interested in watching me do it. Besides, playing with fire and boiling water is a lot of fun... Might make mud pies next


But you are right, and common sense and logic says so - but your proof of logic is amusing none the less. 
However, make sure you apply some of that logic to your mud pies and let the boiling water cool first - unless you think you'll get greater water absorbency into the dirt if it's hot compared to cold water - maybe another experiment there?


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## Scruffy (2/8/10)

Nick JD said:


> Ask yourself this question: what kind of boil is happening in the hidden half of the pot?



Ask yourself: why Nick JD is asking this question? TROLL






Can I just add, I boil my wort in the great outsides in a big pot. I get 17% evaporation right now in winter, (which is fine, I know the numbers, so I can adjust) and between 9-12% at the height of summer...


What was the question?


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## Nick JD (2/8/10)

Thirsty Boy said:


> It's confusing neither myself nor the other people who have done it... You are simply incorrect. The rate at which the entire volume boils is increased. You may think you should be correct... But you aren't.



No, you are incorrect. Isn't conjecture fun? I'll shut up the instant you can prove your theory. Till then it's back to the physics class you said you failed in year 10. :lol:

Anyway I'm currently boiling a kettle of beer with a wonderful handcrafted origami boat floating on it. The seas are rolling, I tell you!


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## PistolPatch (2/8/10)

Doing some experiments in this area will seem silly to some. For example, I personally don't worry about evaporation rates much as I don't have a palate that is able to taste the difference between my single (19% evap) and double batches (9.5% evap) that are both done at a gentle to medium rolling boil.

ThirstyBoy spends a lot of time writing on here helping other brewers. Helping out other brewers can be a very enjoyable sub-hobby of brewing as you get to correspond or meet with a lot of great people. Giving bad advice is something that you never like to find that you have been doing especially with new brewers as they naturally take everything written on a brewing forum as gospel. That is why Thirsty wrote...



Thirsty Boy said:


> I like to be right.... And if I'm going to talk about this stuff and be arrogant enough to advise other people what I think they should do... I want to be sure what I am saying is true, not just that it makes common sense. I'm also arrogant enough to think that some people will be interested in watching me do it. Besides, playing with fire and boiling water is a lot of fun... Might make mud pies next (lol)


A new brewer often finds existing advice on evaporation rates and boil vigour daunting as some people will tell them to either do a good rolling boil, while others will say strive for 8-10% evaporation and brewing software will tell them it should be 15%. WTF does a new brewer do!

Many new brewers will also struggle with one of two things. A new stovetop brewer may struggle to get a good rolling boil going. Another with a large pot on gas might wonder why they are having to use heaps more water than everyone else.

This floatie idea of Thirsty's is a great idea. Mucking around yesterday on the stovetop was enjoyable and because I could "see into" the boil, I now know that putting a floatie in will decrease the amount of energy needed to create a rolling boil and it _*did*_ increase the vigour of the entire boil. And, so it should, as you have applied direct pressure to half the wort surface area. (Putting a lid 3/4 on a half-empty pot applies no pressure to the surface area and therefore doesn't do much to decrease required energy levels. Using a floatie may have also lowered the temperature at which the water boils - I never checked that (wink)).

What the above means I'm not entirely sure of because there isn't much literature out there on evaporation rates and boil vigour that is not based on commercial kettles. I don't know whether boil vigour is more important than evaporation rate or vice versa for example. What the floatie can do though is help us to get _*both*_ things right.

I of course, with my palate will not be able to taste any difference but maybe I'll save 5 cents or $5 on gas or something? I don't really care but I find exploring this stuff is enjoyable and occasionally does result in some forward moves. For example, a year ago a few brewers were enthusiastic and constructive enough to contribute some figures here and from this we have been able to create some automatic formulas in BIAB "software" (though it can be as handy for traditional brewers) as to what evaporation figures they can expect from their particular kettle. In other words it gets them on track quicker.

So for those of you who find all this silly and/or pedantic, just know that there are a few brewers out there whose sub-hobby is exploring things like this and that sometimes it does make a whole new generation of brewer's life far easier and simpler which is obviously a good thing. (Most of the time it just keeps our over-active imaginations/minds amused and results in a shed full of shit  - you should see some of the stuff I have at my place ).

Evaporation rates and boil vigour _*are*_ confusing subjects for new brewers so any concrete and constructive exploration of these, I think, is a real plus. All these long posts unsure and arguments will eventually become some simple advice/formulas for new brewers. The current advice of turning down the heat and/or partially covering the kettle does not help a lot of new brewers. (It certainly didn't help me.)

I think the floatie will help them though so lets not sink it before at least taking it on a little voyage.

Hope this post wasn't too short or anything - lol,
Pat


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## Thirsty Boy (3/8/10)

Nick JD said:


> No, you are incorrect. Isn't conjecture fun? I'll shut up the instant you can prove your theory. Till then it's back to the physics class you said you failed in year 10. :lol:
> 
> Anyway I'm currently boiling a kettle of beer with a wonderful handcrafted origami boat floating on it. The seas are rolling, I tell you!



I'm sure you are having fun with your conjecture, I wouldn't know as what I have been doing is reporting what I actually observe in both experimental and practical situations. I'm not 100% sure that most people would classify that as conjecture.

Interestingly, I could prove you wrong pretty much anytime I want (as a matter of fact you've been proved wrong already at least twice, it's just that you haven't managed to realize it) but I shan't. Its kind of amusing (in an admittedly lazy and somewhat cruel way) to watch as you more and more thoroughly "prove" just exactly what sort of a guy you are.

But I suppose I need to wake up to myself and realize that this exchange with you (and indeed most others I have seen) is simply a waste of time and electrons.... I withdrew from the last thread where we did this for the same reason - but that was someone elses thread, this is mine & I plan to continue using it for the reason I started it. So I shall simply ignore you from this point forwards, you will get no response from me regardless of what you write... Hopefully you will get bored and go away.

Again, the last word on this is yours. Have fun.


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## PistolPatch (3/8/10)

:blink:


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## PistolPatch (3/8/10)

Scruffy said:


> Can I just add, I boil my wort in the great outsides in a big pot. I get 17% evaporation right now in winter, (which is fine, I know the numbers, so I can adjust) and between 9-12% at the height of summer...



This is the sort of post I find_ *really*_ interesting. I hear the above time and time again - the effects of humidity on evaporation. The more people that bother to post informative stuff like the above, the better. Sure, it is one brewer's experience but it is one brewer who is posting without a barrow to push and so my ears prick up.

Donya and thanks Scruffy!
Pat


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## PistolPatch (3/8/10)

rude said:


> Thats why I do a 90min boil, the first half hour is a good rolling boil, then for hop additions I tone it down a tad, towards the end partly cover with the lid
> 
> So I figure the volitiles are boiled away at the start



Another great post. Anyone who bothered to read the article linked in the other evaporation thread would have noticed the problem of losing hop flavour and aroma characteristics in the latter part of the boil. I really like the advice rude offers but is anyone bothering to comment on it? (Don't worry rude, I suggested the something similar in the other thread and it drew no response - lol!)

You certainly have to keep your eyes peeled here for the good posts. Please brewing gods, help the new guys sort the good from the bad!


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## Wolfy (3/8/10)

Scruffy said:


> Can I just add, I boil my wort in the great outsides in a big pot. I get 17% evaporation right now in winter, (which is fine, I know the numbers, so I can adjust) and between 9-12% at the height of summer...





PistolPatch said:


> This is the sort of post I find_ *really*_ interesting. I hear the above time and time again - the effects of humidity on evaporation.


Brisneyland is ALWAYS humid, are you sure that is the (only) cause of the different evaporation rate in winter Vs summer?
Is there no impact from the change in temperature?
(I think wind and related issues would be the biggest factor in either case).


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## Supra-Jim (3/8/10)

PistolPatch said:


> Using a floatie may have also lowered the temperature at which the water boils - I never checked that (wink)).



Hi PP,

Not sure if I'm misunderstanding your comment above, but as I understand it, the floatie increases local pressure (upon the surface of the liquid it is in contact with) and an increase in pressure, increases the boiling point of a liquid. Lower pressure = lower boiling point.

As we are bringing our liquid/wort to the boil we are adding energy, liquid molecules will remain liquid until they have enough energy to overcome the pressure on the surface of liquid and escape. Liquid molecules are also very good at trasnferring their energy through collisions (typcially it is a one sided collsion at the surface of the liquid that allows a molecule to escape as vapour). 

Thinking about this, could the use of a 'floatie' be trapping some of this heat energy in the liquid rather than losing it to the ambient. Hence we get what people seem to be experiencing in practise, a more vigourous boil?

Cheers SJ


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## Wolfy (3/8/10)

@*Supra-Jim*, I think the idea of a 'floaty' is similar to that of an erlenmeyer flask, the base of the flask is wider, but the narrow top makes it appear that the boil is more vigorous than it would then if the surface of the boiling liquid was spread over a larger area. However the shape of the flask also "_slows evaporative loss better than a bigger neck_" or in our case better than an uncovered or unfloaty kettle.

@*PistolPatch*, *Thirsty Boy*'s done all the work and provided all the theories (including the 'cover the pot' idea) - and other than the amusement the experiment has provided for himself and others - I think he's only proving what is logical and sensible (not that there is anything wrong with that).

What would be a good experiment is to extend *Thirsty Boy*'s proof that covering the kettle saves on evaporation losses, to check if the condensate that forms on the lid and falls back into the wort has any negative impacts in terms of DMS or other unwanted byproducts that would usually be boiled off. Do many/most commercial breweries have a cover on their boil kettle, or not? Do the DMS precursors get 'trapped' under the lid and never escape? How much of the kettle should be covered to balance the escaping gasses but save on evaporation losses?

Given that it's now been proven that adjusting the boil intensity allows the brewer to have some control over the evaporation rate, I think the follow-up question is 'What level of boil is adequate?'
Unlike many who feel a vigorous boil is essential, I do not subscribe to the theory that one must 'boil the crap' out of the wort.
For me an uncovered 'soft boil' is what I look for; a good visible amount of convection currents to fully mix the boiling wort and a visible amount of 'steam' rising from the kettle.


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## PistolPatch (3/8/10)

Supra-Jim said:


> Hi PP,
> 
> ... as I understand it, the floatie increases local pressure (upon the surface of the liquid it is in contact with) and an increase in pressure, increases the boiling point of a liquid. Lower pressure = lower boiling point.
> 
> ...



I don't know why I wrote, "lower temperature," SJ. It could have had something to do with posting while under the influence . What you write above makes sense to me .

Wolfy, I think you might have missed reading the figures I measured on the boil I did on Sunday that had the kettle almost completely covered but not fully covered. There was only the tiniest decrease in evaporation rate compared to the non-covered boil.

Cheers,
Pat


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## Nick JD (3/8/10)

Wolfy said:


> For me an uncovered 'soft boil' is what I look for; a good visible amount of convection currents to fully mix the boiling wort and a visible amount of 'steam' rising from the kettle.



Great advice.



Wolfy said:


> @*Supra-Jim*, I think the idea of a 'floaty' is similar to that of an erlenmeyer flask, the base of the flask is wider, but the narrow top* makes it appear that the boil is more vigorous* than it would then if the surface of the boiling liquid was spread over a larger area. However the shape of the flask also "_slows evaporative loss better than a bigger neck_" or in our case better than an uncovered or unfloaty kettle.



More great advice.


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## bum (3/8/10)

PistolPatch said:


> Another great post. Anyone who bothered to read the article linked in the other evaporation thread would have noticed the problem of losing hop flavour and aroma characteristics in the latter part of the boil. I really like the advice rude offers but is anyone bothering to comment on it? (Don't worry rude, I suggested the something similar in the other thread and it drew no response - lol!)


 
I was going to post about this when I initially saw Rude's post basically because I simply thought this would be a great way to save some gas and not reduce the quality of my beer - but then I remembered pils malt. If pils needs a 90min boil to get rid of all the volatiles then I'd assume that they don't disappear quickly. Yes, I understand that pils is s lightly different story but I don't see why pils would need 90min but every other malt would be good to go in under 30min. 

It would be interesting to know if there were some threshold where it doesn't matter any more (i.e. it becomes pretty much imperceptible).


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## Nick JD (3/8/10)

bum said:


> I was going to post about this when I initially saw Rude's post basically because I simply thought this would be a great way to save some gas and not reduce the quality of my beer - but then I remembered pils malt. If pils needs a 90min boil to get rid of all the volatiles then I'd assume that they don't disappear quickly. Yes, I understand that pils is s lightly different story but I don't see why pils would need 90min but every other malt would be good to go in under 30min.
> 
> It would be interesting to know if there were some threshold where it doesn't matter any more (i.e. it becomes pretty much imperceptible).



The use of pils malts and the residual DMS is kinda desirable for some lagers.

_An important malt-derived volatile is dimethyl sulphide (DMS, 4.112), the
flavour threshold of which is 4060 ppb but some all-malt lagers with 100 ppb DMS are
found acceptable. Above this level DMS gives a sweetcorn flavour. DMS is produced by
thermal decomposition of S-methylmethionine (Fig. 4.34), the half-life of which is
reported to be 35 min. at 100C. DMS formed by kilning and wort boiling will be rapidly
lost by evaporation but S-methylmethionine will continue to break down during wort
cooling and the DMS formed then will persist into beer._

_To minimize such DMS formation it is recommended (O'Rourke, 1999, 2002) to use malts with low S-
methylmethionine contents and to extend the wort boiling time to decompose the
majority of the precursor and drive off the DMS. Worts from high-temperature wort
boiling systems contain negligible amounts of DMS and its precursors. It is also
recommended to minimize the whirlpool stand time and to use quick wort cooling to
reduce the time that the wort is held hot.
When wort is boiled with whole hops or pellets, the majority of the hop oil
constituents will be lost during a 6090 min. boil in an open copper. If late hop character
is required a portion (up to 20%) of the hop grist may be added, as choice aroma hops, 5
15 min. before the end of the boil. Early attempts at high temperature wort boiling, with
insufficient venting, produced worts with unacceptable levels of hop oils. Excess
Maillard volatile products must also be evaporated. Figure 9.8 shows the amounts of
various heterocyclic compounds in the vapour condensate during wort boiling. Of
particular interest is 2-acetylthiazole, which has a flavour threshold of 10 ppb in beer, and
must be reduced if not to cause an off-flavour._


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## Supra-Jim (3/8/10)

@Wolfy, one thing also worth noting with an erlenmeyer flask is that the internal surface is very smooth (much smoother than our brewing kettles). This smoothness reduces the nucleation points for bubbles to form on. Hence more heat energy is required to bring the liquid to visibly active boil ( a lesson i unfortunately learnt the hard way when i though i would add a pack of cooper yeast as nutrient 'before' the liquids started boiling, needless to say the nucleation points created by adding the yeast resulted in a geyser of very hot wort all over the kitchen!!).

Hence the vigour boil seen in these style of flasks may be due more to the higher energy contained in the liquid, rather than the shape of the flask (no reference to shape affecting evaporation here).

Cheers SJ


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## Wolfy (3/8/10)

Supra-Jim said:


> ... needless to say the nucleation points created by adding the yeast resulted in a geyser of very hot wort all over the kitchen!!).


I did the same last time I made agar slants, the liquid was so close to the boil when I took it out of the microwave, that by putting in a spoon to stir it the whole lot bubbled up the spoon, over the top of the jug and onto my fingers.

You might be right about the flasks shape, I don't know how to explain the 'floaty' and what people have noticed when trying it, I just keep thinking of something like less surface area hence less evaporation, and more 'energy release' in a smaller surface area hence the boil looks more rapid.


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## bum (3/8/10)

Nick JD said:


> The use of pils malts and the residual DMS is kinda desirable for some lagers.


 Of course. It wasn't my intention to make a sweeping generalisation in regard to the use of pils malts. 



Nick JD said:


> _DMS is produced by
> thermal decomposition of S-methylmethionine (Fig. 4.34), the half-life of which is
> reported to be 35 min. at 100C. _


 
The use of the term term 'half-life' leads me to assume that 35 minutes is not actually the answer to the question I asked. Would that be correct? 

The other stuff is all interesting but I don't have the equipment required to measure my beer down to parts per million. A tongue is about as scientific as my lab gear gets. 

So in terms of Rude's post - is his assumption that the majority of all volatiles should be gone in the first half of the boil a safe one? Of course I understand that it is easy to partially cover the kettle without lid condensation dripping back into the wort re-introducing volatiles - just wondering, is all.


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## Supra-Jim (3/8/10)

Here you go Bum:

Half-life : The time required for one-half of a specified substance to degrade or become inert.

Cheers SJ


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## Nick JD (3/8/10)

bum said:


> So in terms of Rude's post - is his assumption that the majority of all volatiles should be gone in the first half of the boil a safe one?



As far as I understand it, it takes 35 minutes for half the SMM to turn into DMS at 100C. It all depends on how much SMM your malt had.

So if you boil for 30 minutes and then cover (completely) you'll leave about 1/2 more of the DMS in your wort than not covering. How much this is depends on your malt.

If you no-chill then this is even more complicated because SMM is still decomposing into DMS while the wort is slowly cooling. However, it can't decompose in your no-chill if it's (nearly) all gone.

If you had 100ppm at 0 minutes you'd have 50ppm at 35, 25ppm at 70 and 12.5ppm at 105 minutes. Putting the lid on after 30 minutes might give you corn - might not.


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## bum (3/8/10)

That's a few too many ifs for my liking so I'll stick with my current practice for now. Thanks for the explanation.


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## Thirsty Boy (3/8/10)

Wolfy, Pat - I'll repeat what I have said a few times before. The floaty does not just increase the _appearance_ of vigor in the boil, it increases that actual rate at which the liquid boils. I have in fact tested it quite thoroughly.

And its not about pressure... pressure would increase the boiling point and require you to add more energy to get to it, but after that why would it change the boil vigor or the amount of liquid that is boiled off. Although local vapour pressure will also effect evaporation and that's probably playing a part. Wolfy did get the actual reason though.. it is about reducing evaporation (but that's nothing to do with vaporization by boiling) by reducing surface area.

I'll just finish this post then I'll take a while to post up the latest experiments I have been doing. More of the same, sorry - but I'm not particularly interested in the DMS thing. I'm happy I know the answer to that one. You control DMS with length of boil rather than increased vigor.. as long as you are getting the 8-10% per hour, that's enough to strip DMS; and after that its about half life as Nick posted. More DMS calls for a longer not a harder boil.

You will find in them a number of things that are relevant to why the floatie thing works, mainly though I am looking at lids, boil off losses and some of the things I have discussed with Pat.

TB


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## RdeVjun (3/8/10)

Wolfy said:


> I did the same last time I made agar slants, the liquid was so close to the boil when I took it out of the microwave, that by putting in a spoon to stir it the whole lot bubbled up the spoon, over the top of the jug and onto my fingers.


Getting a bit OT here, but that may actually be superheating Wolfy, best explained here, see superheating section down a page or two. The teaspoon provided the nucleation points perhaps. Anyway, I've experienced this myself, it is novel but really no fun when you're on the receiving end. Agar does need to be boiled however...


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## Nick JD (3/8/10)

Thirsty Boy said:


> ...it increases that actual rate at which the liquid boils. I have in fact tested it quite thoroughly.



What's the "rate" at which a liquid boils? 

I thought boiling was the transition of a liquid to a gas. Liquid nitrogen boils at a rate controled by the energy put into it, not its container. 

Am I missing something?


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## Acasta (3/8/10)

Studying Fluid dynamics.
Basic things that may help.
Closing the lid will = more pressure = more heat, therefore i'd imagine more evaporation as its hotter throughout.


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## Scruffy (4/8/10)

Acasta said:


> Studying Fluid dynamics.
> Basic things that may help.
> Closing the lid will = more pressure = more heat, therefore i'd imagine more evaporation as its hotter throughout.


If the lid's still on, look up _condensation _


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## bum (4/8/10)

You have no right to correct him, Scruffy. He has every right to talk whatever nonsense he likes, however.


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## Thirsty Boy (5/8/10)

Is all more complex than poor laymen types like me can understand by just trying to extrapolate what "should" happen. So thats why I'm running a few little tests... I am interested in _what actually happens_ - why it happens is a minor (but interesting) part of it. I'll think about theory and see what explanations I can come up with after I observe the real behavior.

First (moving straight into a contradiction of what I just said I was going to do) - the Pressure Argument. The lid I am using is a round plastic take-away container lid. It weighs 6g and has a radius of 5.5cms. convert that into pressure needed to lift it and you have about - 0.0009psi. Now using a chart I found on engineeringtoolbox.com, you need an extra 0.31psi to raise the boiling point of water from 100C to 101C. So the pressure this lid could apply at best is 3/100ths of that needed to raise the boiling point by 1 degree C. AND - in the combination of this lid and the beakers being used, you can see on the photos there is a gap left at the spout of about 1cm square. So its not even going to be that amount of pressure. This increase might be enough to _visibly_ change the behavior of the boil, but I don't think so. And I also don't think pressure would significantly change the nature of the boil even if it were higher, it would just change the temperature at which things happen.

Second - in these experiments I took into account what Pat had mentioned about the amount of headspace and the surface to volume ratios. So I looked at my brew kettle, which is a decent example of the situations I am trying to address. ie: its a little big for my batch size and I either get too low a boil or too high an evaporation rate using it as it is.
So i worked out how much liquid in the beakers, would give the same wort depth to width (diameter) ratio as I get in my kettle. This was about 400-500 ml in the slightly more than 1L beakers. This results in wort that is about twice as wide as it is deep. I used 400-500ml as the starting volume for all the following tests. This left slightly more than 50% headspace in the beakers.

*SOME STUFF ABOUT LIDS*

(almost all the way on - means lid slightly ajar, perhaps 5 or 6 mm from the outside edge of the lid to the edge of the beaker)

*Lid "almost" all the way on - vs - Lid 2/3rds on... adjust boil vigor*

Beakers filled to 500ml, brought to hard boil and heat off. adjusted back to 500ml with boiling water from kettle. Lids on, flame back on - boil vigor adjusted visually to the same level. boil till one of the beakers hits 200ml.

*Result -* small but definite difference in boil vigor. Final difference in amount boiled off was a small but noticeable decrease for the beaker with the lid mostly on. On the order of 40ml

*Lid 'almost' all the way on - vs - lid 2/3rds on. Equal amounts of heat applied*

Beakers filled to 500ml, brought to hard boil and heat off. Adjusted back to 500ml with boiling water from the kettle. Lids on, flame back on. Beakers swapped from burner to burner every 5 minutes for a total boil time of 30 mins.

*Result -* Medium increase in boil vigor for beaker with lid on. Virtually no difference in amount boiled off.

*Lid 'almost' all the way on - vs - No Lid at all. Equal amounts of heat applied.*

Beakers filled to 500ml, brought to hard boil and heat off. Adjusted back to 500ml with boiling water from the kettle. Lid on one beaker most of the way, flame back on. Beakers swapped from burner to burner every 5 minutes for a total boil time of 30 mins.

*Result -* distinct increase in boil vigor in beaker with lid. Virtually no difference in amount boiled off.

*Lid "fully" on - vs - No lid at all. Equal amounts of heat.*

Beakers filled to 500ml, brought to hard boil and heat off. Adjusted back to 500ml with boiling water from the kettle. Lid fully on one beaker, flame back on. Beakers swapped from burner to burner every 5 minutes for a total boil time of 30 mins.

*Result -* A small but noticeable difference in the amount of liquid boiled off. On the order of about 25-35ml

*Result summary -* In all the cases but one, where the heat applied was the same, the amount of liquid lost was near enough to the same. The exception was the case where the lid was _completely_ on, where a small decrease in boil off was observed.

There was an observable increase in boil intensity in all cases where a lid was on to any extent at all, with a larger increase where the lid was closer to being fully on.

In the case where the boil intensity was "matched", the lid being more "closed" resulted in the amount of liquid lost being reduced by an observable, but with the precision of the scale used, not very measurable amount.

*Conclusions - * (or speculations really) Any decrease in evaporation that might be brought about by placing a lid on a boiling vessel, will be (roughly) balanced by the increase in vaporization brought about by an increase in boil intensity when the lid is placed on the vessel. So unless an effort is made to balance the vigor of the boil in the vessel, putting a lid on will not decrease the amount of liquid lost during the boil. Although a reduction might be seen if the lid completely closes the pot, this may present other brewing problems.

If however the boil intensity in a vessel with a lid (even less than fully on) is reduced to match in intensity the boil before the lid was put on... then a reduction in the amount of liquid lost will be observed.


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## Thirsty Boy (5/8/10)

*SOME MORE STUFF ABOUT LIDS*

The conclusion from my last experiments depends on the observation that boil intensity increases noticeably when you put on a lid, even partially. So.... is it true or is it just my imagination? It being true supports my pre-conceptions, and perhaps the decreases in liquid losses are just due to me turning down a boil that had in fact not increased in intensity at all. So to be certain, I better test it to make sure I am observing something real rather than something I just want to see.

*Boil Intensity in a vessel with a lid - vs - Boil Intensity in a vessel without a lid given the same amount of applied heat.*

1 beaker, filled to the 400ml mark and brought to hard boil, heat reduced and boil adjusted to a very low boil/simmer. Maintain boil without adjusting flame for several minutes to let it "settle". Count the number of bubbles produced in one minute. (bubbles were considered to be countable when they reached the top of the liquid and caused an observable ripple as they broke the surface.)

Without adjusting flame, put a lid fully on the beaker. Allow to settle for several minutes, count bubbles produced in one minute.

Repeat the counts with lid off and lid on several times to lessen the impact of changes in gas pressure, ambient temp, breeze etc.

Repeat the series of tests again, but instead of putting the lid all the way on the vessel, only put it "halfway on".

*Results -*

Lid fully on tests

1. Off = 56 bubbles. On = far more than I could count. Hundreds.
2. Off = 40 bubbles. On = far more than I could count. Hundreds
3. Off = 68 bubbles. On = far more than I could count. Hundreds.

Average with Lid Off = 54.7
Average with Lid On = More than countable, hundreds.

Lid Half on Tests

1. Off = 60 bubbles. On = 107 bubbles
2. Off = 50 bubbles. On = 95 bubbles
3. Off = 43 bubbles. On = 77 bubbles

Average with Lid Off = 51
Average with Lid Half On = 93

*Conclusions*

I wasn't imagining it. Putting a lid even partly on a boiling vessel increases the intensity of the boil quite significantly. This is in little beakers though and I imagine that it would be less noticeable in larger vessels with a higher volume to surface area ratio.


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## Thirsty Boy (5/8/10)

*STUFF ABOUT EVAPORATION VS VAPORIZATION*

Evaporation is where molecules of a liquid, in this case water, just break off from the surface of a body of liquid and wander off into the atmosphere. it happens at room temperature, but happens a lot faster when the liquid is hot. A bunch of other things affect evaporation too.

When a liquid is heated beyond its boiling point, liquid changes state to gas and bubbles away. The liquid stays the same temperature once it reaches its boiling point and any extra energy added goes into changing liquid to gas. I think the term is vaporization, but am not sure. For my purposes here, thats what I'm going to call it at any rate, sorry if I am getting it wrong.

Surely in a boiling liquid, the vast majority of liquid lost will be from vaporization rather than evaporation? I think thats its less clear than you might suspect. Let test it.

*Volume lost when you Boil the Liquid*

Beaker filled to 500ml, brought to hard boil and heat off. Adjusted back to 500ml with boiling water from the kettle. Heat back on and heat turned to lowest pre-set. This gives a boil that in a brew kettle I would call medium to medium-high. Boil for 30 mins.

*Result -*

Start Volume = 500ml
End Volume = 225ml

Total boiled away in 30min = 275ml = 550ml/hr

*Volume lost to evaporation in nearly boiling but still water*

Beaker filled to 500ml, brought to hard boil and heat off. Adjusted back to 500ml with boiling water from the kettle. Heat back on and turned down until all signs of boiling stopped. Thermometer placed at about half depth, attempt to maintain heat at as close to 100 as possible without letting any actual boil happen. Maintain for 1hr.

*Results -*

Able to keep the temp between 93 & 97 for the vast majority of the hour. It slipped to 89 for a minute or two, and once or twice it broke into actual bubbles getting to the surface for a few seconds before I managed to adjust the heat down.

Start Volume = 500ml
End Volume = 325ml

Total volume Evaporated = 175ml/hr

*Volume lost to evaporation in a vessel that is heated to boiling, then removed from the heat totally*

500ml into beaker and brought to a hard boil. Adjusted back to 500ml with boiling water from the kettle. No more heat applied to vessel. Leave for an hour.

*Result -*

Start Volume = 500ml
End volume = 450ml

Total Volume Evaporated = 50ml
(see, that proves it wasn't just me getting the fire wrong.. Happens significantly even with no extra heat)

*Conclusion/Speculation*

In a boiling vessel, liquid is lost to the atmosphere in two different way. By the obvious bubbling away of steam through vaporization & by the less obvious process of evaporation which occurs even if there is no vaporization happening at all.

Although the results above would almost certainly not be directly transferable to brewing sized vessels, in the above test it seems that given a total loss of 550ml/hr in a boiled vessel, at least 175ml/hr or 32% of the water lost could be ascribed to evaporation rather than vaporization. And considering that in a boiling vessel the temperatures would be even higher than in the test, and the surface area would be vastly increased by the fact that it was being stretched, agitated and wobbled etc by the boiling action... It seems to me that the percentage would actually have been even higher. Now vaporization increases with boil intensity, so the ratio of evaporation to vaporization would drop as boil intensity increased the amount of total vaporization, with the evaporation staying relatively constant. Increasing the volume to surface area ratio would have a similar effect of increasing the importance of vaporization vs evaporation and the visa versa is also true.

While the total effect will be variable from brewery to brewery - measures taken to reduce/increase evaporation in a brew kettle will reduce/increase the total amount of liquid lost during the boiling period. Not as dramatically as measures taken to reduce or increase boil vigor (assuming you always maintain a reasonable amount of actual active boiling) but certainly by amounts that could be significant.


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## Wolfy (5/8/10)

Thirsty Boy said:


> *Conclusions - * (or speculations really) Any decrease in evaporation that might be brought about by placing a lid on a boiling vessel, will be (roughly) balanced by the increase in vaporization brought about by an increase in boil intensity when the lid is placed on the vessel. So unless an effort is made to balance the vigor of the boil in the vessel, putting a lid on will not decrease the amount of liquid lost during the boil. Although a reduction might be seen if the lid completely closes the pot, this may present other brewing problems.


I do not doubt the conclusions based on what you observed in the conditions of your experiment.
However, I'd suggest that, the conclusion that the lid fully on 'might' reduce evaporation, is simply the result of the artificial test conditions - small plastic lid, beaker with a large spout etc - and that those conditions do not match real life cooking or brewing conditions enough to validate extending it to those situations. Most saucepans, pots and brew kettles have heavy close fitting lids, so I'd like to see the same experiment repeated with two larger sized pots, one with lid on and one with lid off (or just use the same pot and the beaker to measure before/after volume with the same flame/boil intensity for the same period of time).


Thirsty Boy said:


> ...
> 1 beaker, filled to the 400ml mark and brought to hard boil, heat reduced and boil adjusted to a very low boil/simmer. Maintain boil without adjusting flame for several minutes to let it "settle". Count the number of bubbles produced in one minute. (bubbles were considered to be countable when they reached the top of the liquid and caused an observable ripple as they broke the surface.)
> ...
> *Conclusions*
> I wasn't imagining it. Putting a lid even partly on a boiling vessel increases the intensity of the boil quite significantly. This is in little beakers though and I imagine that it would be less noticeable in larger vessels with a higher volume to surface area ratio.


Again I am not questioning the results you observed, however this time I'd like to question your interpretation of 'boil vigor', is counting the number of bubbles released at the surface an adequate or even satisfactory measure of 'boil vigor'. By putting a lid partly over the container you are changing the conditions at the liquid/gas interface, which as you observed changes the number of bubbles released. However, is this extended all the way through the boiling container, or is it only a surface effect? What would you observe if you used some food coloring or semi-floating balls in the liquid, would putting a lid on change the behavior of all the liquid in the container or just that at the surface?

My logic for this question is as follows: Given that a 'rolling boil' is usually recommended for brewing so that there is a good exchange of liquid from the bottom of the kettle to the top, if someone followed your conclusion and used a lid to cover 1/2 of their kettle so they could turn down the gas but still have what appears to be the same 'boil vigor', would they actually still be getting a complete 'mixing' due to convection currents and other process within the boiling wort as a whole, or does it only change what is observed at the surface?


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## Nick JD (5/8/10)

Key words: *Vapour Pressure* and *Latent Heat of Vapourisation/Evaporation*.

Check it out Thirsty - it'll explain a lot for you. It's the same phenomenon that controls the rate at which your clothes dry on the line depending on the humidity of the air. Same thing that makes a hot day okay because it's a "dry" heat.

Filling the layer above the liquid with saturated vapour by putting a lid (even partially) on means not nearly as much of the molecules on the surface of the liquid (and on the "surface" of the rising bubbles) can "change" into their gas state as easily. This has a massive impact on the system and it's something you have completely disregarded. A++ for effort though.


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## drsmurto (5/8/10)

Nick JD said:


> Key words: *Vapour Pressure*.
> 
> Check it out Thirsty - it'll explain a lot for you.



It's not quite that simple though Nick, once you open up that can you need to take into account atmospheric pressure, relative humidity, temperature, wind speed above the kettle and let's not even start discussing how the density of a fluid changes the relative vapour pressure.

We could start a discussion about the laws of thermodynamics and fluid dynamics......I am already salivating at the thought and my jeans are suddenly a tad more restricting...... :huh: :lol: 

Sorry for the off topic, I'll go back to my mechanistic study of ketone oxidation :icon_drool2:


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## Nick JD (5/8/10)

DrSmurto said:


> It's not quite that simple though Nick, once you open up that can you need to take into account atmospheric pressure, relative humidity, temperature, wind speed above the kettle and let's not even start discussing how the density of a fluid changes the relative vapour pressure.
> 
> We could start a discussion about the laws of thermodynamics and fluid dynamics......I am already salivating at the thought and my jeans are suddenly a tad more restricting...... :huh: :lol:
> 
> Sorry for the off topic, I'll go back to my mechanistic study of ketone oxidation :icon_drool2:



It's the "lid on" stuff I'm refering to, Doc.

EDIT: although it probably does relate somewhat to the winter/summer boil losses discussed earlier.


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## drsmurto (5/8/10)

Nick JD said:


> It's the "lid on" stuff I'm refering to, Doc.
> 
> EDIT: although it probably does relate somewhat to the winter/summer boil losses discussed earlier.



Ah, missed that. Carry on.


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## Thirsty Boy (5/8/10)

Remember... I don't really care "why" I care what happens. If evaporation, vaporization or vigor changes with a lid on... Great, if it doesn't... Great. Don't care, just want to know if. Why, I am happy to think about after I know what.

Wolfy... Measuring boil intensity by bubbles. I agree, but measuring the velocity of the wort was a bit beyond me. Anyway, most of the movement and velocity pretty obviously comes from the bubbles... They form at the bottom and rise to the top stirring the wort as they go... Sure not all of them make it to the top because they don't have enough vapor pressure, which is why I was only counting the ones that did make it to the top... In a brew kettle we can't see through the wort, so we need to judge boil vigor by what we see on the surface, and that means mostly how much it is disturbed and the amount of bubbles . It's probably far from a perfect model to say that twice as many bubbles equals twice as vigorous, (which is why I didn't suggest anything like that) but I can't see that a boil with more bubbles in total forming and breaking the surface isn't going to also be more vigorous than one with less. Or am I missing something obvious? The boils were obviously more vigorous to look at.... The bubbles were just a way to try and stick a number to it in an attempt to remove my observer bias as much as I could.

The Lid fully on thing... Absolutely, that lid isn't the same sort of thing as a proper brewing lid. It almost certainly wouldn't emulate a proper close fitting heavier lid all the way on a brewing pot. Actually, that was part of the situation I wanted to test... I don't think that absolute pressure inside the pot would terribly effect the outcomes of these tests... So using a lid that wasn't capable of causing any significant increase in gross pressure was a way of mostly taking that out as a variable. If something was happening, it wasn't happening because of an increase in total pressure. Any lid at all would produce the same increase in local vapor pressure and temperature, so in the lid partly on tests the light plastic lid was as good as any other.

That was my thought process anyway... Anymore holes you can pick? (don't be too thorough though or I'll have to do all the damn tests again)

Thanks for taking the time to think about it.

TB


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## Wolfy (5/8/10)

Thirsty Boy said:


> Anymore holes you can pick?


No more holes, just that both my comments were related to real life (non experimental) observations:

I _know _that when I cook if I put the lid fully on the saucepan it will not (usually) boil dry, however if I don't put the lid on (and still cook/boil for the same time/intensity) then most often things will boil dry on me (I even managed to boil dry some _soup _the other day - go figure!). So from that perspective, I'd have thought that having the lid 'fully on' would make a huge difference to any losses, not just minor, minimal or perhaps no change as your experiment showed.

When I 'boil' my wort, with my kettle/setup/ideal boil, I do not see masses of bubbles on the surface as per your beaker experiment, what I see instead is a large 'convection bump' from the hot wort rising from above the (electric) heating element and breaking the surface - kindof like one big continuous bubble. So I was interested/concerned as to how putting a lid partly on would impact the convection currents within the wort, since in my case that is where most of the mixing comes from not from the 'bubbles'. But as you pointed out for your experiment most of the 'mixing' of the water is due to the bubbles rising from the bottom rather than any 'convection currents'.


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## Thirsty Boy (6/8/10)

I see what you mean, I seem exactly the same thing in my kettle... But that convection bump is full of bubbles and I don't think it's just, or even mostly from convection, I think its a stream of bubbles combined with convection thats causing am pretty fast wort flow.

I don't know if this is true, but it seems to me that if it was purely, or even mostly convection - that bump would be there before the wort boils. Does 99 degree water convect at so much slower a rate than 100 degree water? Yet the major disturbance to the surface only happens after the bubbles start. Convection currents of course happen - But for instance in my HLT... 2400W at the bottom doesn't even produce enough mixing by convection currents to give an even temperature through the vessel... The top can be at 90+.... While under the element it's only 75 or 80, yet let it start to actually boil, with bubbles reaching the surface... And then it becomes uniform mighty fast as the rising bubbles mix things up.

Might not be the case, but that's the way it seems to me.

I'm surprised by the lid results too.... I thought that pretty much no matter what the circumstance, a lid would reduce liquid lost.... Seems it's not that cut and dried. I suspect a full lid in a large pot would make for a much more distinct result. But I also suspect that that might have a lot to do with reflux, and has been mentioned before, too much reflux could be a bad thing. I don't think it's anything like a problem if you are talking about a lid partially, even most of the way on, that you are using to cut back on excessive liquid loss - but if a lid can be an issue, one that's all the way on, and cutting down liquid loss by a significant margin.... That'd be where the issue's gonna be found. I'd certainly never put a lid all the way on the brew pot and leave it there, I don't think I've ever suggested it... Lid all the way on testing for me has just been a way of demonstrating the most extreme end of the "Lid on vs Lid off" comparison. I'm not sure that I have managed to test it though. The light lid and the always there gap at the spout might have rendered those tests more of a "Lid really really nearly all the way on" test instead. Which is less valid from a point of trying to illustrate the extremes... But perhaps more relevant?? Maybe.

Thanks heaps for your input


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## Thirsty Boy (6/8/10)

I see what you mean, I seem exactly the same thing in my kettle... But that convection bump is full of bubbles and I don't think it's just, or even mostly from convection, I think its a stream of bubbles combined with convection thats causing am pretty fast wort flow.

I don't know if this is true, but it seems to me that if it was purely, or even mostly convection - that bump would be there before the wort boils. Does 99 degree water convect at so much slower a rate than 100 degree water? Yet the major disturbance to the surface only happens after the bubbles start. Convection currents of course happen - But for instance in my HLT... 2400W at the bottom doesn't even produce enough mixing by convection currents to give an even temperature through the vessel... The top can be at 90+.... While under the element it's only 75 or 80, yet let it start to actually boil, with bubbles reaching the surface... And then it becomes uniform mighty fast as the rising bubbles mix things up.

Might not be the case, but that's the way it seems to me.

I'm surprised by the lid results too.... I thought that pretty much no matter what the circumstance, a lid would reduce liquid lost.... Seems it's not that cut and dried. I suspect a full lid in a large pot would make for a much more distinct result. But I also suspect that that might have a lot to do with reflux, and has been mentioned before, too much reflux could be a bad thing. I don't think it's anything like a problem if you are talking about a lid partially, even most of the way on, that you are using to cut back on excessive liquid loss - but if a lid can be an issue, one that's all the way on, and cutting down liquid loss by a significant margin.... That'd be where the issue's gonna be found. I'd certainly never put a lid all the way on the brew pot and leave it there, I don't think I've ever suggested it... Lid all the way on testing for me has just been a way of demonstrating the most extreme end of the "Lid on vs Lid off" comparison. I'm not sure that I have managed to test it though. The light lid and the always there gap at the spout might have rendered those tests more of a "Lid really really nearly all the way on" test instead. Which is less valid from a point of trying to illustrate the extremes... But perhaps more relevant?? Maybe.

Thanks heaps for your input


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