# Excessive Kettle Evaporation Loss



## sshann001 (26/7/10)

I have just tested my kettle before I do my first BIAB brew, and I have found that I lose around 30% of my total kettle volume for a 1 hour boil. My kettle is a Big W 19L SS pot. Has anyone else experienced losses this large? I notice that Beersmith has 5-15% of total volume as a guide.


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## benno1973 (26/7/10)

Percentages are fairly misleading when calculating evap loss. Evaporation occurs at a volume rate (i.e. 5L per hour) rather than at a percentage rate. So if your original boil volume is low, you'll notice that the evaporation percentage is quite high. 

For an extreme example, think about boiling 1L or wort for an hour. Chances are, it'd boil dry. That's not 5-15%, that's 100% evaporation loss. If you're boiling only around 15L (which I'm guessing that you would be with a 19L pot), 30% evaporation would mean you'd be losing around 5L over the hour, which isn't excessive. I boil around 28L to end up with around 23L in the kettle, so I have a similar volume loss, but the percentages seem much more reasonable.

Obviously, evaporation rate is affected by numerous other factors, not least of which is how vigorous the boil is. You want a rolling boil, but it doesn't need to be violent. If you think you're boil is too high, just turn the gas down a little and you're evap loss will drop as well.


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## thylacine (26/7/10)

I use same kettle. Start boil with 18 litres, after 90mins 15l remains. I measured every 30 min for the first few brews. 1 litre every 30min consistently. I used a somewhat gentle rolling boil as opposed to a vigorous one. Grain bills usually 33.2 to 3.5kg base, 300-400g spec. Fifteen litre wort in fermenter. Cheers...


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## bkmad (26/7/10)

You will get a higher percentage when doing a smaller volume boil. In simple terms (not taking into account different surface area for different sized kettles), you might boil off 4L from a small 16L boil, giving a high 25% boil off. With a larger boil you may still only boil off 4L but for a boil size of 30L you only have 13% boil off.


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## Nick JD (26/7/10)

I can easily boil 30% of say, 16L in a 19L pot in 60 minutes on the electric stovetop element. Frequently do.

The issue here is that a smaller volume has a much larger surface area proportion than a larger volume. More of the liquid comes in contact with the surface and more of the liquid at the bottom circulates to the top.

These two things are important when boiling small volumes: more rapid circulation, and bigger surface area/volume ratio.

The common two methods to fix the issue are: to boil a jug of water and top up your boil occasionally; or to reduce the heat significantly. 

I do the second one - and while it appears that you are now no longer maintaining a "rolling boil" I've found that you still get acceptable evaporation losses due to the factors above taking lots of the DMS with it. 

And you save money on power or gas.


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## mika (26/7/10)

A 'rolling boil' is simply one that's turning the wort over in the kettle, there's no need for it to be jumping up and trying to reach for the roof. You'll find a steady rolling boil makes it a lot easier to deal with hop additions as well.


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## Nick JD (26/7/10)

mika said:


> A 'rolling boil' is simply one that's turning the wort over in the kettle, there's no need for it to be jumping up and trying to reach for the roof. You'll find a steady rolling boil makes it a lot easier to deal with hop additions as well.



A rolling boil is a boil that when stirred it will still keep boiling. 

In a 19L pot, this type of boiling will result in excessive evaporation losses.


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## sshann001 (26/7/10)

Thanks to all. Good to hear that it is not out of the ordinary. I will adjust the vigour of the rolling boil, and see how that helps.


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## rude (26/7/10)

Good topic Shannbrewer as after hearing some answers I think I might be over doing it

I start with 34 L & finish with 25 L in the cube with maybe 1 to 2 L loss in the kettle never measured it

I use free gas though boil hard for the first 30 mins then depends on how I am going (check evap with dip stick) I'll slow it up a bit.

Sometimes Im getting a bit low I,ll put the lid half on

Is there any detriment to boiling too hard ?


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## rude (26/7/10)

90 min boil there too


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## Thirsty Boy (27/7/10)

Nick JD said:


> A rolling boil is a boil that when stirred it will still keep boiling.



That's a terrible definition of a rolling boil... BUT, I think it might well be the simplest, easiest and most understandable way to describe how to TELL if you have a rolling boil that I have ever heard!! Nice.

Now to disagree with you - 

In a boil, you need to get two things to happen, and you need to work out a balance that allows you to do it. 

1] You need to get a certain amount of evaporation - NOT - an amount in litres, a percentage! in order to be sure that you have evaporated your DMS, aldehydes, bad tasting hop compounds and other unwanted volatile compounds, you want to evaporate a _minimum_ of 8% of your starting volume per hour

2] You need to maintain a physical movement of the wort and the formation of bubbles which reach the surface. This is your rolling boil... the wort needs to physically roll and churn around the kettle, and bubbles need to form. The physical agitation and bubbles allow much of the chemistry in the boil to occur - a lot of protein chemistry happens on the surface of the bubbles, hop chemistry happens under physical force, volatiles come out of the wort and ride up to the surface inside the bubbles.

So - turning a boil down to the point where it no longer "rolls" cuts one of those aspects out. If you have a high surface area pot, you will still get the needed evaporation at a simmer, but you miss the agitation part.

Now you could just leave your flame up, boil and evaporate a large fraction of your beer - BUT - Heat load is bad for beer. The more heat you have to chuck at a wort in order to get it to meet conditions 1 & 2 - the less the final beer likes it. Too much heat load can effect flavour, colour, flavour stability, haze stability and propensity to staling. In general, less heat is better. Boiling "too hard" can do several of the same things and also mess up protein coagulation by breaking apart the bonds in the coagulated proteins and causing them to partially re-dissolve.

Now if your pot has a high surface area - it takes more energy shoved into the bottom to maintain a given level of rolling boil, heat is escaping through the surface (as increased evaporation) and you have to whack more in to get the same level of physical agitation in the wort.

So your high surface area ratio pot is hitting you with a double whammy - in order to maintain a rolling boil you are evaporating more liquid than is convenient or necessary, and to do it you are having to shove in more energy and higher heat load than is ideal (less being better) - you cant reduce your heat load or your evaporation by turning the heat down, because that will kill your boil vigour off. So what do you do??

Well ideally you get yourself a taller narrower pot, where you can natively get a good rolling boil and 8-15% boil off. Normally that's going to be a pot that will give you _roughly_ a 1:1 ratio between the depth of your wort and the width of your wort. But that's a pretty loose target and will vary a fair bit.

The other way is to somehow reduce the surface area of your pot. The obvious way is to put a lid partially on - all sorts of people will tell you that a lid is a bad idea, but that's only true if you let too much of the liquid that condenses on it drip back into the pot (re-introducing the volatiles that have previously evaporated) A third on, Half on... its just not going to be an issue. If it still sounds like a bad idea - you could get tricky and use a tinfoil hat that allowed the opening to be partially covered.. but channel any condensation away to the outside of the pot. Or, you could do what I do, which is float something on the surface of the liquid. That way anything that evaporates stays evaporated, but the surface area of the liquid is reduced anyway. In a smallish pot, you could just float a takeaway container or a heatproof bowl in there. Experiment with different sized things till you find one that allows you to keep your rolling boil, turn down your heat and maintain a lower % evaporation rate.

Back to disagreeing with Nick - Because I believe the above stuff to be true, and actually think its fairly important for beer quality, I think that to turn down your heat below the point of a rolling boil in order to cut evaporation losses (as Nick says he does) is basically a bad idea. I think a lid partially on, something floating on the surface of the boil, or ultimately a more appropriately shaped pot is preferable. That way any issues, small large or imagined are avoided, its not actually any harder or more complex; and you still solve your problem.

And his way of telling whether a boil is a rolling boil or not is still a cracker, and how I plan to describe it from now on.

Thirsty


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## QldKev (27/7/10)

Good write up Thirsty. In my case I have always done what I would consider a strong rolling boil, but without boiling the sh!te out of it. I aim for 14% evap loss, one pot being a keggle shape kettle. Next time I may try the idea of floating something to reduce the surface area, and aim for a 10% boil off. I think lately I have had my beers slightly darker than to style, not much just a bit, and maybe this is from my caramelising some wort. Also the added benefit of better protein coagulation would also be excellent.

QldKev


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## MeLoveBeer (27/7/10)

QldKev said:


> Good write up Thirsty.



+1, always educational Thirsty :icon_cheers: 

My understanding was that a rolling boil was one where the rising bubbles actively shape the surface and a simmer was where the bubbles rise but the surface remains flat. I like the idea of floating something to reduce the surface area and evap rate... will give that a crack this weekend (currently getting high evap rates and having trouble supplying enough sparge water with my tiny HLT to compensate)


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## MHB (27/7/10)

Again well put TB, and I to like Nicks description of a Rolling Boil.

In part where it's getting complicated is that all the research is done on big industrial kettles and we are talking about small domestic applications bound to be some confusion.

As a rule of thumb I would want to see 10% of the Knockout Volume (i.e. what you are putting in our fermenter) evaporated to ensure adequate stripping of volatiles. So for a 25 L batch 2.5 litres of evaporation.

When you are boiling a concentrated wort you would still need that same 2.5 L even tho it might be more than 10% of the kettle contents it's still 10% of the wort

MHB


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## Nick JD (27/7/10)

Thirsty Boy said:


> That's a terrible definition of a rolling boil... BUT, I think it might well be the simplest, easiest and most understandable way to describe how to TELL if you have a rolling boil that I have ever heard!! Nice.
> 
> Now to disagree with you -
> 
> ...



Or, you turn your stove's heat-o-meter to a heading of 275W maintaining what those in the Piss-Poor Brewing Monkey-Business call "A Wiggly Boil". I will take a video next time that will better describe this elusive creature.


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## Thirsty Boy (27/7/10)

MHB said:


> Again well put TB, and I to like Nicks description of a Rolling Boil.
> 
> In part where it's getting complicated is that all the research is done on big industrial kettles and we are talking about small domestic applications – bound to be some confusion.
> 
> ...



Actually that's one of the reasons why I think the old 8-15% rule is still a good one to follow... Lots of people will point you towards current research that talks about breweries that are only getting 3-4% boil off... But you are looking at modern kettles with internal calendria or even external boilers, wort strippers, low pressure dynamic boiling etc etc. And a home brewer just hasn't got any of that gear... We cant even close down the stack on our kettle to cut back evaporation a little.

The 8-15% thing however is an old rule of thumb that was developed when kettles were smaller, the heating method of choice was a flame under the bottom or at most a steam jacket and frequently even an open topped kettle. A hell of a lot closer to what you'll find in a home brewery.

Hell, brewing is a pretty forgiving process.. You're gonna have to try pretty hard to spoil your beer in the mash tun or kettle - but of all the ways I can think of, an inadequate boil is the one I think is most likely to come back and bite you.

If in doubt.... Too hard is way better than too soft.

TB


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## Nick JD (27/7/10)

Thirsty Boy said:


> Too hard is way better than too soft.



Freud would have a field-day with ya, Thirsty. :lol:


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## manticle (27/7/10)

Thirsty Boy said:


> you could get tricky and use a tinfoil hat



This doesn't work

http://people.csail.mit.edu/rahimi/helmet/


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## Nick JD (27/7/10)

My guessing-o-meter says that reflux in wort boiling is bad. The steamy stuff needs to piss off. 

Less steamy stuff = less piss off water = goodness beer. YEAH!


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## PistolPatch (29/7/10)

Thirsty Boy said:


> Hell, brewing is a pretty forgiving process.. You're gonna have to try pretty hard to spoil your beer in the mash tun or kettle - but of all the ways I can think of, an inadequate boil is the one I think is most likely to come back and bite you.
> 
> If in doubt.... Too hard is way better than too soft.
> 
> TB



This whole area is not researched very well as it all "boils" down to kettle shape and volume.

Working on percentages doesn't work very well practically. For example, in my 70L pot, if I do a single batch my evaporation rate is around 19%. At the same boil vigour, if doing a double batch, my evaporation rate is about 9.5%. Both brews taste the same. You can see some evaporation figures in this file.. 
View attachment BIABrewer_Register.xls

(My figures are the PP ones.)

Unless you know my kettle shape and boil volume telling me to make sure I achieve an evaporation rate of _x_ percent is silly. Telling me I need to boil off _x_ litres per hour is silly.

The only practical advice that can be offered to another brewer until an impractical amount of research is done is to advise the good rolling boil. Anything less than this can quickly start to bring haze problems etc, etc..

Anyway, all I have found is the following and many people will disagree with it but I am a pretty good measurer when so inclined. I went through a stage where I went to great lengths to reduce my evaporation rate. All I now know is that...

1. Putting a lid over a kettle like mine (a straight-sided pot) did not do much to reduce the evaporation rate. Putting the lid even 3/4 over my kettle made little, if any difference.

2. Reducing to a simmer also made no or little difference.

I couldn't understand this at the time as so many people here told me it would. I then did some reading on the physics of evaporation and now understand well why 1 and 2 above were true.

Regarding 1 above, just think of your electric kitchen kettle. Most of the steam is out the spout before it even has a chance to even think of evaporating .

Regarding 2 above, this will take some reading up on the physics of liquids but basically there is little difference between a simmer and a gentle boil. In many "physical" ways they are the same. In other words, once you reach a critical point (the simmer) many things stay the same.

So, until us home brewers do a massive amount of research (which won't happen), a good rolling boil is the safest way to go. Concentrating on figures is certainly not the way to go.

Spot,
PP


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## Thirsty Boy (30/7/10)

PistolPatch said:


> This whole area is not researched very well as it all "boils" down to kettle shape and volume.
> 
> Working on percentages doesn't work very well practically. For example, in my 70L pot, if I do a single batch my evaporation rate is around 19%. At the same boil vigour, if doing a double batch, my evaporation rate is about 9.5%. Both brews taste the same. You can see some evaporation figures in this file..
> View attachment 39750
> ...



Using percentages to "work out" your boil off is silly, agreed. But, (and I am starting to run out of ideas about how to differently explain this to people who seem persistently unable to get it) THATS NOT WHAT YOU ARE SUPPOSED TO USE THEM FOR.

You measure you boil off... In litres per hour. That's how you are going to work out you start and finish volumes. Easy. Now that you have that.... You, convert it into a % figure. If that % figure is above 8% you are good... Stop worrying and go back to thinking in litres per hour. Done.

If your rate is low, In a given pot you can, absolutely, done it many times, physics says I should be able to do it and I have - change the boil off rate by increasing the amount of heat put in and thus the vigor of the boil. Turn up the gas and boil harder - more liquid will boil off. Reducing it isn't so easy, but reducing it isn't the goal.

In your double batch... You get 9.5% - great, that's all you want to know, nothing to change. If you do a single though, you are getting 19% - and that to me would indicate that you are putting in more heat than ideal. You have a high surface area to depth ratio, and in order to maintain an acceptable rolling boil, the heat flux through your pot is higher than it need be, lower heat flux is better.

So you can turn down the heat... Which kills your rolling boil (bad) and you still get mostly the same boil off anyway, or put on a lid, which also only minorly effects the boil off until it's almost all the way on. So those two options are no use are they? BUT, what is less obvious, is that you get a much more active boil when lids are even part on..... So you drop the heat, which lowers the boil, but then you pop a lid partially on, which makes the boil pick back upmto where it was. And the combination of the lid and the lower heat flux, will drop your evaporation too. Remember, the goal isn't particularly to have a low evaporation..... The high evaporation is simply an _indicator_ that something else is not as it should be - and you need to take action to fix it.

In your case the high evaporation rate is telling you that your 70L pot is too big to do single batches in. If you want to keep your heat flux low and not have to worry about topping up anyway. Lid mostly on, heat down lower....back a few percent to under 15% ... And that's all that's needed. Or you buy a smaller slimmer pot for single batches, where everything happens as it should without interference. But we aren't all made of money so a solution that doesn'tmcost a whole new pot would be nice - As I said, my preferred option is to float something on the surface of the boil.... Insant reduction in surface area to depth ratio, heat gets turned lower to maintain the boil level, evaporation rate drops to let me know its working and thus instant resolution of problem. 

It's not about the "figures" and obsessively trying to get them right. It's about understanding what the figures are telling you about what's happening in the boil.... The figures you hear bandied about aren't just there for fun, because that's what the writer of the text book got and therefore so should you. They are the figures that "indicate" that all is well, or not!

If you boil off 8-15% of your kettles starting volume per hour.
AND
If you have a nice rolling boil the whole time you are boiling
THEN
All is well 

If you have a lower or higher boil off, no matter what the size or shape of your pot, then there are things about your boil that could be considered less than optimal  and you might like to consider changing something.

That's all those figures are.. Little hints about where you can look for improvement, or where you might find problems hiding. You use them as you will.

TB


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## Screwtop (30/7/10)

Thirsty Boy said:


> Using percentages to "work out" your boil off is silly, agreed. But, (and I am starting to run out of ideas about how to differently explain this to people who seem persistently unable to get it) THATS NOT WHAT YOU ARE SUPPOSED TO USE THEM FOR.
> 
> You measure you boil off... In litres per hour. That's how you are going to work out you start and finish volumes. Easy. Now that you have that.... You, convert it into a % figure. If that % figure is above 8% you are good... Stop worrying and go back to thinking in litres per hour. Done.




Spot on TB, been trying to get this across for a long time. Boiloff percentage is important as above 8% all of the processes required of a boil are achieved. But for calculations of total brewing liquor or pre boil volume a % is pointless, for this a known boil off volume in litres is required. Beersmith uses the boil off % when calculating total brewing liquor, the result can be confusing to the brewer. Any time batch volume is altered from the default, open Beersmith's equipment details on the recipe page and change the boil off % to reflect your known boiloff volume in litres. This provides correct total brewing liquor and all targets should be close, depending upon variables such as ambient atmospheric conditions where you operate your kettle.

Screwy


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## thylacine (30/7/10)

"...Or, you could do what I do, which is float something on the surface of the liquid. That way anything that evaporates stays evaporated, but the surface area of the liquid is reduced anyway. In a smallish pot, you could just float a takeaway container or a heatproof bowl in there. Experiment with different sized things till you find one that allows you to keep your rolling boil, turn down your heat and maintain a lower % evaporation rate..."

Floating an object in my 19L kettle right now. It made an instant boil out of a simmer. (18L boil on gas stove-top). When I floated my hop bag I could turn the heat down even more.

Thanks TB


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## PistolPatch (30/7/10)

What a great idea thylacine! Love it. A totally simple way of reducing the wort surface area :icon_cheers:.

There's hope for me yet Thirsty getting my evap rates down on the single batches .

Thanks and :beer:,
Pat


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## King Brown (30/7/10)

After reading TB's post I understand why people do 2 hour boils for certain styles. Having a short and fat brewpot I think I'm gonna have to try the method of floating something on top of the wort for my next batch. Lot's of great info in this thread.


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## PistolPatch (31/7/10)

My apologies and queries...

Thirsty, I was just re-reading your post above and I see that I have given credit to thylacine for floating something in the kettle (here and on BIABrewer.info) whereas it was your post above that first mentioned it. (I'll correct the BIABrewer.info post* I made when I finish here but thanks to you also thylacine. Thirsty's posts are as long as mine so without yours I would have missed the floatie bit entireley ).

My only query for you Thirsty is the bit where you say that having a lid part on lowers the evaporation rate by giving you a boil with a higher vigour. The increased pressure of a partly covered kettle is minimal and the wort surface area does not change. The change in evaporation rate is miniscule.

This is what I was trying to say about the physics of evaporation. My personal experience and physics tells me that, with a flat lid covering 3/4s of your kettle, very little difference will be noticed in evaporation rate. There is little difference in evap rate once you reach a simmer.

It's all fun though and I might even do some experiments this weekend as a matter of interest with my 70L and 20L pots just with water as I find this sort of thing quite interesting.

More simmering/boiling/measuring and less talk I reckon ,
Pat

*Corrections made here.


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## Nick JD (31/7/10)

If you float something on your beer does it lose carbon dioxide slower? 

The evaporation is happening _in the bottom of the kettle_ in those little bubbles of gas called _water vapour. _Unless you're simmering.


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## beerbog (31/7/10)

As someone stated before, you can control your loss by varying the boil intensity, ensuring you have a rolling boil to start with. 

Your kettle opening diameter is important too.

I can vary mine anywhere from 4 - 5 litres per hour for a 40cm diameter kettle just by changing the aggressiveness of the boil. :beerbang:


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## Thirsty Boy (31/7/10)

PistolPatch said:


> My apologies and queries...
> 
> Thirsty, I was just re-reading your post above and I see that I have given credit to thylacine for floating something in the kettle (here and on BIABrewer.info) whereas it was your post above that first mentioned it. (I'll correct the BIABrewer.info post* I made when I finish here but thanks to you also thylacine. Thirsty's posts are as long as mine so without yours I would have missed the floatie bit entireley ).
> 
> ...



Your lid may perhaps function differently to mine - mine, when put partially over the kettle, cuts the evaporation rate down by a small but noticeable amount.... your reading of the physics of the matter is different to mine, but I gave physics up after second year uni and so might be wrong.

Besides... as I have tried a couple of times to point out... it isn't the actual evaporation rate that matters -- the evaporation rate is indicative of other things. If you put a lid partially on your pot, as anyone who has ever even boiled an egg can tell you, the pot boils harder... so in order to get the pot boiling at the same vigour, you can turn the heat down - and that's what you want to do - add less heat for the same boil vigour, which will as a consequence, reduce your evaporation rate. A lid is a way to do this, something floating on the boil is a way to do this, a pot with a smaller surface area is a way to do this

You need to evaporate 8% of your starting volume per hour - that is a given for volatile removal. Above that point, your evaporation rate is a tool for you to use, to help you understand how your boil is performing.

TB


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## manticle (31/7/10)

Nick JD said:


> If you float something on your beer does it lose carbon dioxide slower?
> 
> The evaporation is happening _in the bottom of the kettle_ in those little bubbles of gas called _water vapour. _Unless you're simmering.



Not quite sure if I've misinterpreted what you're saying but it seems akin to suggesting that if CO2 can escape a vessel that isn't sealed so can water vapour. If that were exactly the case, placing a lid on something wouldn't effect evaporation loss which we both know is not correct. Placing something like a foil takeaway container sounds like it would act like a small lid - if water vapour does hit it it will condense and reform into a liquid state.

CO2 vapour and water vapour have different properties

Sorry if I've misunderstood.


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## bum (31/7/10)

Thirsty Boy said:


> float something on the surface of the liquid. That way anything that evaporates stays evaporated, but the surface area of the liquid is reduced anyway.


 
Genius. Never would have thought of this. 

Manticle, that link may only be used to mock the paranoid. Your attempt to use it for borderline relevant reasons in an affront to decency.


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## Nick JD (31/7/10)

manticle said:


> Not quite sure if I've misinterpreted what you're saying but it seems akin to suggesting that if CO2 can escape a vessel that isn't sealed so can water vapour. If that were exactly the case, placing a lid on something wouldn't effect evaporation loss which we both know is not correct. Placing something like a foil takeaway container sounds like it would act like a small lid - if water vapour does hit it it will condense and reform into a liquid state.
> 
> CO2 vapour and water vapour have different properties
> 
> Sorry if I've misunderstood.



The bubbles of water vapour that rise in the rolling boil when they hit the object floating on the surface will move around it and into the atmosphere just the same as a CO2 bubble will go around an ice cube. The foil container will be very close to 100C - not a great condenser, most likely doing zero condensing. 

The only reason a lid causes less less evaporation is because condensed water is refluxing back into the pot. 

Let's take this to the extreme and imagine a kettle at rolling boil _entirely _covered with a floating object. What will happen then? Will all the rising water vapor bubbles strike it and recondense? Or will it find one area that will be jetting out vapour?

Convection currents will force more of the rising bubbles away from the floating object and the rolling boil will be more intense on the other side of the object.

And again - evaporation is happening at _the bottom of the kettle_ in a rolling boil.


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## Thirsty Boy (31/7/10)

Nick JD said:


> The bubbles of water vapour that rise in the rolling boil when they hit the object floating on the surface will move around it and into the atmosphere just the same as a CO2 bubble will go around an ice cube. The foil container will be very close to 100C - not a great condenser, most likely doing zero condensing.
> 
> The only reason a lid causes less less evaporation is because condensed water is refluxing back into the pot.
> 
> ...



Except for the inconvenient fact that I float something in my boil every single time I brew... and it both increases the vigour of my boil and decreases the evaporation... markedly.

Therefore your theory disagrees with empirical observation and is thus incorrect.


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## Nick JD (31/7/10)

Thirsty Boy said:


> Except for the inconvenient fact that I float something in my boil every single time I brew... and it both increases the vigour of my boil and decreases the evaporation... markedly.



And you have your heat setting the same?

Breweries use Batch Rectification techniques when all they need to do is get a whole stack of Chinese Takeaway containers? :lol: 

Bubbles of water vapour will get into the air regardless of obstacles - read up on vapour pressure. Emperical observation favours the observer's bias.


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## Thirsty Boy (31/7/10)

Nick JD said:


> And you have your heat setting the same?
> 
> . . . . . Emperical observation favours the observer's bias.



ahhhh - no. What with having specifically stated that I turn the heat down and that the _object_ of the exercise was in fact to be able to turn the heat down.... I kind of thought that was implicit.

Empirical observation is how science works... observer bias is simply something to be accounted for in experimental design.


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## Nick JD (31/7/10)

Thirsty Boy said:


> ....be able to turn the heat down...



So you are seeing increased vigour in the boil - but obviously only in the area that's not covered - right? 

How much of the surface is covered by the floating object?

Can you refer me to some science on how this under-takeaway-container-condensation works? 

I say you'll get the same result from just boiling less vigorously and leaving the floatie off.


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## Thirsty Boy (31/7/10)

Nick JD said:


> So you are seeing increased vigour in the boil - but obviously only in the area that's not covered - right?
> 
> How much of the surface is covered by the floating object?
> 
> ...



Why yes you would, approximately - for the evaporation rate part... which as I have been at pains to point out is the indicator, not the object. The boil vigour increases, as it does if you put a lid on a pot, allowing you to turn the heat down - which is the point. I don't need to refer you to science texts... Instead I refer you to the kitchen where anyone can try it and see. Give it a wee go... if it doesn't work, then pop back and let us know how right you were.

as for the vigour of the boil only being increased in the areas "not" under the lid -- perhaps thats true... I see a general increase in wort movement, a larger number of bubbles breaking the surface and generally a lot more activity in the kettle. It may be my imagination, or it may be your observer bias in action... but I have been homebrewing from grain for 5 years and I work in a professional brewery, I have observed literally thousands of wort boils over the years, and in my opinion, the boil vigour with the float is higher than without - if it weren't, I wouldn't do it.


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## manticle (31/7/10)

I'm a little bit confused Nick. Empirical observation seems to be good enough for your brewery regardless of science and you seem to expect others to take you at face value (or at least try it before canning it) . Why is Thirsty's experience less valuable than yours?

Or is that the joke?


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## beerbog (31/7/10)

Just boil the bastard! :beerbang:


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## Nick JD (31/7/10)

Thirsty Boy said:


> It may be my imagination, or it may be your observer bias in action...



It may be. It may not be.

That is the question. This is the question:
_
"I have just tested my kettle before I do my first BIAB brew, and I have found that I lose around 30% of my total kettle volume for a 1 hour boil. My kettle is a Big W 19L SS pot."

_I'm just not that sure that "float a takeaway container on the surface" is a great answer. _

_


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## bradsbrew (31/7/10)

Flame suit is well and truely on BUT would you lose less to evaporation using water as opposed to wort?


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## Thirsty Boy (31/7/10)

> I'm just not that sure that "float a takeaway container on the surface" is a great answer.



Well, that's our actual difference then - I _am_ sure its a good answer, its the solution I effectually use to solve exactly the same issue.

As equally I am sure you believe that your proposed solution of turning the heat down so you get less than a rolling boil is an effectual solution. - I don't actually just believe it, I know that what you propose _will_ in fact work to reduce evaporation, I just think that it has other potential issues attached that make it a less than ideal solution.

What you seem to have been doing though, is telling me that I am imagining or misinterpreting an effect that I can both clearly see and in fact measure (I have) ... I will object to this quite strongly and tell you that you're wrong. If on the other hand you were to say something along the lines of "OK, that obviously works, but I think its a bad idea anyway because......" then its a different story. You put your case, I put my case - everyone including the OP can decide for themselves which (if either) of us is right and with any luck at all, someone learns something about brewing on the way.

This is the point is it not?


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## bum (1/8/10)

Nick JD said:


> I'm just not that sure that "float a takeaway container on the surface" is a great answer. _
> 
> _


 
Dude, you're a cock but you're only a moron when you will it - why are you deliberately misrepresenting his well reasoned position? It only undermines your point when you try to reduce his stance to a small statement when he has gone to great lengths to explain and present many options in regards to the issue. You're making a caricature when everyone else can see real life.


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## MHB (1/8/10)

> Flame suit is well and truely on BUT would you lose less to evaporation using water as opposed to wort?


Actually no - the higher the concentration of dissolved matter the lower the rate of steam loss, given all the other variables stay the same. Quick intro in Wiki

Honestly I can't believe this thread has dragged on to its third page, once you get a liquid to its boiling point it can't get any hotter. Any energy not lots in other directions is available to change liquid to vapour (heat of vaporisation), more heat means more evaporation.

If you want to lower the rate of evaporation turn the heat down.

MHB


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## PistolPatch (1/8/10)

Morning Mark ,

One thing I don't understand is what are the main problems with having a high evaporation rate apart from needing more water and maybe a bit more gas? I think a lot of new brewers using pots with wide surface areas can get hung up on evaporation rate figures and try and "fix" them by simmering their wort etc instead of boiling it which is a mistake.

As I mentioned above, my evaporation rate for double batches is 9.5% and %19 for singles. The beer tastes the same to me though I am not claiming to have a super advanced palate.

So, are there any differences in the quality of wort produced in large surface area pots i.e. those with high evaporation rates? If not, shouldn't we just concentrate on maintaining the good old rolling boil and put up with needing a bit more water and possibly gas?

Cheers to you,
Pat


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## MHB (1/8/10)

Morning Pat

The only thing I can say about brewing, with any confidence is that there is rarely a "Right" answer, there are lots of wrong ones, good ones and even better ones.

Wort boiling is a very complex process, we aim to do lots of things all at the same time, the list usually includes - Killing unwanted bugs, reducing the amount protein, ending all enzyme reactions, bittering the beer and removing unwanted volatiles (from both hops and malt) and another half dozen other minor jobs.

To do all of these and to do them properly we need to get a certain amount of energy into the wort that amount of energy will cause about 8-10% of the wort to evaporate.

There are obvious downsides to not putting in enough energy, namely that the above aren't achieved, and problems caused by putting in too much, principally wort darkening and precipitating too much protein (reducing head) stripping of desirable volatiles (good smells) - Oh and your burning $ for no gain.

If you can get the optimum ("Right" ) amount of heat into the kettle (and no more) you will get the best outcome, you know you have the right amount by measuring the evaporation and getting that 8-10% evaporation rate. I know it's hard to tell while the boil is in progress, but that's part of getting to know your system. Simmering isn't the bogey people make out, if you're getting the desired evaporation rate mission accomplished. 

Good starting read from the IBD View attachment 02___The_function_of_wort_boiling1_1_.pdf

MHB


PS
Lid's off, the first things to condense are the higher boiling point compounds, putting a lid on encourages these to fall back into the kettle unwanted volatiles need to be carried away by the steam so don't block the escaping vapour.
M


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## PistolPatch (1/8/10)

Hey, thanks for the above Mark - a good read as usual .

So, for my 45cm diameter pot, my double batches are spot on. When I single batch though even when I have tried simmering, the evaporation rate has still been way above this 8-10% and I did end up with wort clarity problems which I never get with my good rolling boil.

So, the way I am reading all this I should leave my double batches as is and give Thirsty's floatie a try on my single batches. Hopefully I have got this right? (Mind you I am not really worried as the beer tastes fine to me )

From reading the article, one further thing that maybe we could do given the poor shape of home brew kettles, is to perhaps slow the boil down to a simmer for the flavour and aroma additions so as to "preserve the more late hop characteristics"???

Thanks again mate,
Pat


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## Nick JD (1/8/10)

MHB said:


> Any energy not lots in other directions is available to change liquid to vapour (heat of vaporisation), more heat means more evaporation.
> 
> If you want to lower the rate of evaporation turn the heat down.



Well said.


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## Nick JD (1/8/10)

bum said:


> Dude, you're a cock but you're only a moron when you will it - why are you deliberately misrepresenting his well reasoned position? It only undermines your point when you try to reduce his stance to a small statement when he has gone to great lengths to explain and present many options in regards to the issue. You're making a caricature when everyone else can see real life.



Because I know that if one turns their heat down and then covers half the surface the uncovered half will appear to boil twice as strongly - all the vapour is forced to leave the kettle in only half the area. This is not a more vigourous boil, it's a bottleneck in the release of vapour. The same net vigour and evaporation will happen without the floating object at the same temperature ... it's just simple physics.


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## Thirsty Boy (1/8/10)

PistolPatch said:


> Morning Mark ,
> 
> One thing I don't understand is what are the main problems with having a high evaporation rate apart from needing more water and maybe a bit more gas? I think a lot of new brewers using pots with wide surface areas can get hung up on evaporation rate figures and try and "fix" them by simmering their wort etc instead of boiling it which is a mistake.
> 
> ...



Pat,

Go back a page or two, I explained some of the potential issues with high heat loading on worts. And I repeat, yet again... That high evaporation is not the issue... It is an indicator of an issue. So as mark says, it just tells you whether you are in safe territory, or whether there could be issues.

And yes, if you believe that heat load is a factor in wort/beer quality, then high surface area pots, which require a higher heat load to maintain a given level of boil vigor, *can* effect the quality of the beer. Of course if you don't think that's true, then it's not particularly important.

I absolutely disagree with Mark on the simmering thing... IMO it _is_ a bugbear, the 8% thing is only part of the picture in a boil, the physical agitation and bubble formation in an active rolling boil, both play important parts in the chemical changes that take place in the kettle... You don't get them in a simmering boil. I might bang on about people reducing the heat load on their kettle, but thats only because people generally aren't aware that too much heat can be an issue, at the end of the day...i'd much rather see any brewer shoving a bit too much heat through their kettle than see them with an insipid boil.

Your 19% boil is only a little outside what most people would consider the "acceptable" parameters, it's high but not insane. You've said previously that you can't tell the difference between your double and single batches, so to you it's obviously not a problem.... Why worry about it?


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## MHB (1/8/10)

Maybe I phrased it badly enough energy to get ~10% evaporation isn't going to be a simmer, nor is the wort going to be jumping out of the kettle but I think if your evaporation is close to target your getting enough of a boil to achieve all the goals.

Agreed a simmer isn't usually adequate, but I do like Pilsner Urquell, it's reportedly boiled at what could be called a very low boil for 2 hours. So I sort of suspect that Shorter/Harder Longer/Softer boils achieve the same thing.

You know you're getting an adequate boil by measuring your evaporation as a percentage and adjusting you brewing process to hit the targets, just like in crushing grain, mashing or sparging the experience gained in one brew feeds into improving the nest.

MHB


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## Thirsty Boy (1/8/10)

Nick JD said:


> Because I know that if one turns their heat down and then covers half the surface the uncovered half will appear to boil twice as strongly - all the vapour is forced to leave the kettle in only half the area. This is not a more vigourous boil, it's a bottleneck in the release of vapour. The same net vigour and evaporation will happen without the floating object at the same temperature ... it's just simple physics.



Not simple physics... Your overly simple interpretation of a complex physical system.

But you know best... I must be wrong - after all, I only do it, have measured the results, have formally studied wort boiling and am experienced in observing the phenomenon in question. Stupid of me to think for even an instant that could lead to a valid conclusion.

I'll on deluding myself into thinking that things I can see, measure and understand are real.. Everyone else should listen to you.


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## Thirsty Boy (1/8/10)

MHB said:


> Maybe I phrased it badly enough energy to get ~10% evaporation isn't going to be a simmer, nor is the wort going to be jumping out of the kettle but I think if your evaporation is close to target your getting enough of a boil to achieve all the goals.
> 
> Agreed a simmer isn't usually adequate, but I do like Pilsner Urquell, it's reportedly boiled at what could be called a very low boil for 2 hours. So I sort of suspect that Shorter/Harder Longer/Softer boils achieve the same thing.
> 
> ...



Absolutely. But dependent on an assumption about kettle architecture. In breweries, where kettles are designed for the purpose.... 10% or so evaporation is an indicator that your boil will have been vigorous enough. And that's why we all use the 8-15% range... But home brewers aren't using vessels designed for purpose... They are frequently using vessels that are a serious compromise between volume, cost and flexibility. And that invalidates the assumption about kettle architecture. My brewery for instance is primarily designed for single batches. With my heat source and my normal pre-boil volume, an ideal pot would be about 40L, I would get a great rolling boil and about 12% boil off. BUT - I want to be able to do the odd double batch, so I have a 60L pot instead, and its too big (in diameter). If I put enough energy into it to get a decent boil vigor, I get around 18-20% boil off, and if I try to go with an "acceptable" boil off, I get a truly insipid simmer instead of a boil. So in order for that safe range to apply, I change my kettle architecture. So that's why, in raw terms of driving off volatiles, 8% is enough no matter the shape or size of your kettle.... But it's only an effective indicator of boil vigor in a pot that is close to ideal. Poor old home brewers are left to try and judge what is an adequate boil vigor in the pot they have... And how many threads, including this one, go into that question?

I'm in your camp anyway I reckon.... Most boils I see in other home brewers systems are far more than adequate, mine is a chunk more gentle and I suspect there is many a home brewer who would classify it as too much like a "simmer"


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## Kieren (1/8/10)

Thirsty Boy said:


> Not simple physics... Your overly simple interpretation of a complex physical system.
> 
> But you know best... I must be wrong - after all, I only do it, have measured the results, have formally studied wort boiling and am experienced in observing the phenomenon in question. Stupid of me to think for even an instant that could lead to a valid conclusion.
> 
> I'll on deluding myself into thinking that things I can see, measure and understand are real.. Everyone else should listen to you.




:lol:


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## Nick JD (1/8/10)

Thirsty Boy said:


> I'll on deluding myself into thinking that things I can see, measure and understand are real.. Everyone else should listen to you.



No - I think they should listen to you, Thirsty - but I also think they shouldn't have a lid on their kettle, I think they should just turn down their boil a little. 

SMM-->DMS happens at 100C and DMS has a boiling point of 37C. You simply don't need a magama pit to get rid of the unwanted volitiles.

Lidding pots because you say it's a good idea might encourage other brewers to do it, when they don't need to. It's bad practice. I can get the required evaporation from my kettle with the lid almost completely on and the heat turned waaay down. There's a shitload of refluxed DMS getting back into the wort though. I stopped doing this because it was bad practice.


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## bum (1/8/10)

Nick JD said:


> [Doing 'X'] because you say it's a good idea might encourage other brewers to do it, when they don't need to. It's bad practice.


 
Is anyone else lolling/raging pretty hard right now? 

The irony is delicious/infuriating. 

But in terms of your specific frame of reference, TB has specified it is best practice to set it up so that the condensation does not drip back into the wort. Assuming a brewer achieves this where is the harm? Serious question, btw, not stirring the pot. I'm asking because what TB has said seems reasonable and in practical terms the only thing you've present against the idea is "I think you are wrong".


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## Thirsty Boy (1/8/10)

Nick JD said:


> No - I think they should listen to you, Thirsty - but I also think they shouldn't have a lid on their kettle, I think they should just turn down their boil a little.
> 
> SMM-->DMS happens at 100C and DMS has a boiling point of 37C. You simply don't need a magama pit to get rid of the unwanted volitiles.
> 
> Lidding pots because you say it's a good idea might encourage other brewers to do it, when they don't need to. It's bad practice.



Have you actually read any of my previous posts in this thread? Seriously... I have _repeatedly_ suggested that what you really want to do is turn your heat down... That the whole point of trying to reduce evaporation is not to reduce evaporation, but to reduce the heat load on your wort... By turning the heat down. that in general... Your heat should _always_ be as low as it can be whilst actually doing the things that need to be done in a boil

But, boils are about more than driving off dms, first there are a host of other unwanted volatiles in a wort, and second volatiles are far from the whole picture. Turning the heat down to a simmer, also effects the way the other parts of the boil happen... It has bugger all to do with DMS. DMS you can fix with a simmer and the appropriate amount of time.

Once again, you interpret over simply, something which is complex.

You put a lid on a _simmering_ boil, and it's bad practice from two perspectives.... If you were to put a lid partially on an over evaporative boil in a kettle that has too much surface area in the first place - so that you are able to turn the heat down and maintain both your active boil and a sufficient boil off rate?? that might be a slightly different thing perhaps?

Anyway, everything reasonable that needs to be said has already been said. More than enough for people who actually read all the words to come to a sensible conclusion. I'm out of this thread. All yours if you want unopposed right of reply mate.


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## yardy (1/8/10)

http://www.homebrewdownunder.com/index.php?topic=609.0

some info here on this as well

Dave


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## Peter Wadey (1/8/10)

Sorry,
I could not be bothered reading page after page of this stuff, but as far as not putting your lid on because of the condensate dripping back in, 
surely that's a minor hurdle to conserving a little energy (lid partially on, so heat can be turned down a little) ?
I made a little clip years ago that I use to prop the lid up a little bit on the down side so that the condensate drips outside the kettle.
Somebody might find the pics useful.








This last one just to show the whole picture....the lid is usually off a bit more than this during the boil.


Rgds,
Wad


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## Nick JD (1/8/10)

Peter Wadey said:


> Sorry,
> I could not be bothered reading page after page of this stuff, but as far as not putting your lid on because of the condensate dripping back in,
> surely that's a minor hurdle to conserving a little energy (lid partially on, so heat can be turned down a little) ?
> I made a little clip years ago that I use to prop the lid up a little bit on the down side so that the condensate drips outside the kettle.
> ...



That's a great idea - Thirsty, you could do this instead of refluxing all your DMS.


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## bum (1/8/10)

Apart from spelling out the clip usage how is that any different from how Thirsty suggested it be done in his first post?


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## manticle (1/8/10)

Didn't thirsty posit almost exactly that in his first post on the subject?



> you could get tricky and use a tinfoil hat that allowed the opening to be partially covered.. but channel any condensation away to the outside of the pot.



Not sure how this:


> you could do what I do, which is float something on the surface of the liquid.


 is going to reflux ALL your DMS back into the boil. If it does, I guess thirty's beers all taste like creamed corn and he just doesn't know the difference.


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## SpillsMostOfIt (1/8/10)

Edit: I got sucked into arguing on the Internet.


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## Nick JD (1/8/10)

manticle said:


> Didn't thirsty posit almost exactly that in his first post on the subject?
> 
> 
> 
> Not sure how this: is going to reflux ALL your DMS back into the boil. If it does, I guess thirty's beers all taste like creamed corn and he just doesn't know the difference.



In the other thread Thirsty started about evaporation I asked:

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

A. 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. _ 

He's advocating allowing reflux. On this thread he's not.

Now I don't know what to do with my lid :unsure: :unsure: . I think I'll just leave it off.


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## manticle (1/8/10)

My interpretation is that any reflux that comes from floating a foil takeaway container on the top of a kettle he's already suggested is too large for the purpose will be minimal and the volatiles will find another way out. I think you're making too much of this. Just try it for yourself and see - if it makes no difference to your own brew then report back here and say so.

It's odd that you're arguing theory over practical experience but I think you're arguing it with people who already have a decent grasp of theory. Regardless - put your own principles into practice and try it before dismissing it.


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## Peter Wadey (1/8/10)

bum said:


> Apart from spelling out the clip usage how is that any different from how Thirsty suggested it be done in his first post?



Hi,
I don't know what you mean.
There was no mention in his 1st post about how the lid could be left on & condensate not drop in.

".......The obvious way is to put a lid partially on - all sorts of people will tell you that a lid is a bad idea, but that's only true if you let too much of the liquid that condenses on it drip back into the pot (re-introducing the volatiles that have previously evaporated)'

In his 3rd post he wrote:
"We cant even close down the stack on our kettle to cut back evaporation a little."

I have simply illustrated how the 'stack' can be closed off some without the condensate from the lid dropping back in. That simple. Nothing more.

Wad


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## MHB (1/8/10)

Nick JD said:


> Now I don't know what to do with my lid


I've got some ideas!

Mark


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## Nick JD (1/8/10)

manticle said:


> My interpretation is that any reflux that comes from floating a foil takeaway container on the top of a kettle he's already suggested is too large for the purpose will be minimal and the volatiles will find another way out. I think you're making too much of this. Just try it for yourself and see - if it makes no difference to your own brew then report back here and say so.
> 
> It's odd that you're arguing theory over practical experience but I think you're arguing it with people who already have a decent grasp of theory. Regardless - put your own principles into practice and try it before dismissing it.



My interpretation came from what I posted above. We're not talking about a floating container - we're talking about a lid.


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## Nick JD (1/8/10)

MHB said:


> I've got some ideas!
> 
> Mark


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## Thunus (1/8/10)

MHB said:


> I've got some ideas!
> 
> Mark



U were just too quick for me Mark :icon_cheers:


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## manticle (1/8/10)

Nick JD said:


> . We're not talking about a floating container - we're talking about a lid.




I don't really know what we're talking about anymore.


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## Nick JD (1/8/10)

manticle said:


> I don't really know what we're talking about anymore.



I wonder if the poor guy who asked about how to reduce the evaporation rate in his 19L pot does? I said something about a rolling boil, gave the guy my experience in the subject (I boil in a 19L pot) and then Thirsty went a wrote a freakin essay.

Why did the chicken cross the road?

You want the answer, or Thirsty's version?


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## manticle (1/8/10)

Was quite happy with both versions until it became a war.*

*internet war


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## bum (1/8/10)

Peter Wadey said:


> Hi,
> I don't know what you mean.
> There was no mention in his 1st post about how the lid could be left on & condensate not drop in.
> 
> ...


 
I was in no way inferring that anything you posted was wrong, inadequate or even just rehashing something already said. I'm sure your post was and will be useful to many. My question to Nick about his response to your post was based in the fact that the way I see it your pictorial post seemed in many ways to demonstrate things Thirsty had already either clearly said or inferred and I was able to join the dots for myself. The use of clips aside (an elegant solution I wouldn't have thought of there, btw) your pictures pretty much reflect what I was imagining TB was getting at in parts of his posts - posts that Nick seems vehemently opposed to. I hope this has made my earlier post a little more clear. (Although reading this one back I suspect I might have managed to do the exact opposite. Sorry if this is the case.)


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## Nick JD (1/8/10)

manticle said:


> Was quite happy with both versions until it became a war.*
> 
> *internet war


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## manticle (1/8/10)

bum said:


> I was in no way inferring that anything you posted was wrong...............



Implying?


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## bum (1/8/10)

Oh, it's on now, bitch!

[EDIT: Actually, at first I just thought you were correcting my possible misuse of the word "inferring" - hence the joke above. But now I'm not so sure. If it seems I'm slighting anyone else I'd like a little clarification as to whom since I might be being a little dense at the moment.]


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## thylacine (1/8/10)

TB:
Love the 'floating container', wish I heard of it earlier. My stove struggles to boil 18L in my 19L Big W pot (wider than tall). With the lid mostly on it just does a gentle boil. Now, with a magical floating container, I get the same boil without the lid. And when the hop bag joins the flotilla, a 'vigorous' boil. 

I've learned to look forward to your input (eg. "essays"). In fact when I see YOUR name attached to a thread I don't skip over it. Ta...


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## Nick JD (1/8/10)

thylacine said:


> TB:
> Love the 'floating container', wish I heard of it earlier. My stove struggles to boil 18L in my 19L Big W pot (wider than tall). With the lid mostly on it just does a gentle boil. Now, with a magical floating container, I get the same boil without the lid. And when the hop bag joins the flotilla, a 'vigorous' boil.
> 
> I've learned to look forward to your input (eg. "essays"). In fact when I see YOUR name attached to a thread I don't skip over it. Ta...



You boil 18L in a 19L pot with a vigorous boil? I'd love to see that!


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## MHB (1/8/10)

Nick
You we all know by now that you won't shut up until you gets the last word 

A big part point of the discussion (for want of a better term) is that you shouldn't be boiling 18L in a 19L pot, its unsafe for one and more importantly it limits you ability to make good beer.
I've read enough of your posts to conclude that you are either impenetrably obtuse or just so frigging tight you could sharpen pencils in your anus.

Please put me back on ignore I find it much more peaceful
Mark


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## Nick JD (1/8/10)

Be B) my esteemed retailer. No one boils 18L in a 19L pot ... at 100C 18L is 18.72L and in my obtuseness even I couldn't believe that anyone has even attempted it, let alone commented on it working - hence, my comment.

Yours,

Sharp Pencils.


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