Kettle Evaporation -

[Nick JD]

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?

 

[rude]

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

 

[raven19]

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?

 

[Thirsty Boy]

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?

 

[Wolfy]

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?

 

[Scruffy]

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?

 

[Nick JD]

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!

 

[PistolPatch]

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...

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

 

[Thirsty Boy]

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.

 

[PistolPatch]

:blink:

 

[PistolPatch]

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

 

[PistolPatch]

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!

 

[Wolfy]

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.

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).

 

[Supra-Jim]

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

 

[Wolfy]

@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.

 

[PistolPatch]

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.

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

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

 

[Nick JD]

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.

@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.

 

[bum]

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).

 

[Nick JD]

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.

 

[Supra-Jim]

@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