# Kettle Evaporation Rate



## fraser_john (16/7/07)

In the past I have "estimated" my kettle evaporation rate, and it has been a dismal failure. Tomorrow night I am planning on a true experiment by measuring in 40 litres of water and doing a full hours boil and chilling through the CFC to get my rate figured out once and for all.

Have others done this or do they do their best estimation as well? If so, complete the polls so we get an idea.

Personally, I use a converted keg, I had an extra 6 inches of height welded in so I can do a full vigorous boil of a 38 litre batch without fear of a boil over.


----------



## Trent (16/7/07)

Fraser John
I use a converted keg (a legally aquired old 18 gallon job), and I find that I dont lose so much a percentage, as a fairly set figure. I lose about 3L per hour with the lid half on, whether I am brewing a 23 or 46L batch. 
May aswell do a brew, and put in a known quantity of water/wort, boil it like normal, and run that through your CFC, and that way you will have a good idea of how much you will lose per hour, and you will also have a beer to brew. Maybe make it a brown porter with only a bittering hop, so that way if you end up with more, or less, the bitterness wont be affected TOO much.
All the best
Trent


----------



## razz (16/7/07)

G'day fraser_john. I'm not sure why you selected those ranges. It may be easier for members to reply if you used something like 5-10%, 10-15%, 15-20% and so on, food for thought. This is a good poll and hopefully will get plenty of comment. I boil for 90 minutes with a 42 litre batch and usually boil off 8-10 ltrs. I get a really good foaming/rolling boil going, it makes for a great beer. One of the main reasons for good head retention in the finished beer.


----------



## bugwan (16/7/07)

I allow for 17% loss in a 50L alum pot per hour. It usually turns out to be quite accurate. I'm quite surprised that it's that high, but I generally give it a good rolling boil on the NASA.


----------



## PostModern (16/7/07)

Evaporation tends to be function of the surface area of the top of the liquid and amount of heat applied rather than of the volume. I boil off about 4 litres per hour, regardless, it seems, of my starting volume.

eg, if you had one litre in the pot, after an hour boiling would you have 800mL left?


----------



## fraser_john (16/7/07)

PostModern said:


> Evaporation tends to be function of the surface area of the top of the liquid rather than of the volume. I boil off about 4 litres per hour, regardless, it seems, of my starting volume.
> 
> eg, if you had one litre in the pot, after an hour boiling would you have 800mL left?




That is probably a very good point! In that case, in order to determine true % rate, it would have to be done at full batch size, so either 19 litre batch or 38 litre batch, each evaporation rate would be different!

Thanks!


----------



## Tony (16/7/07)

mine is 50 to 55 liter batches in a converted 18 gallon keg

i get 14.5L/Hr with a good rolling boil over a rambo burner

cheers


----------



## AndrewQLD (16/7/07)

Calculating your evaporation rate based on % is a waste of time IMHO. If you boil for 60 minutes with a wort volume of 29 lt on my system I would lose 6 lt or 20%, but if I boil 58 lt using the % method I should lose 12 lt, but in reality I still only lose the 6lt over an hour boil. So you should really be looking at your losses as lt/hour.

Your chiller has nothing to do with your evaporation losses, as the wort cools it 'shrinks" by about 4% and this is called shrinkage. You would count that towards your efficiency into fermenter.

Ideally the best way to calculate your boil off losses is in the kettle after the boil has ended and before it is chilled, I use a calibrated dip stick marked in 2 lt increments.

Cheers
Andrew


----------



## ozpowell (16/7/07)

fraser_john said:


> That is probably a very good point! In that case, in order to determine true % rate, it would have to be done at full batch size, so either 19 litre batch or 38 litre batch, each evaporation rate would be different!
> 
> Thanks!



Makes me wonder why Beersmith uses a %age for it's brew-ware setup. I've never really thought about it before because I always do batches with the same volume, but it really should be a volume rate of loss rather than a percentage.

Cheers,
Michael


----------



## bugwan (16/7/07)

AndrewQLD said:


> .
> .
> .
> .
> ...



Is it calibrated to allow for the expansion of liquids at high temperatures  Just being a smartarse...  

I always boil for an hour and a half and always brew 23Ltr batches, so my allowance for a 17% loss works well. If I was doing different boil lengths, I'd come up with a better method...


----------



## Jye (16/7/07)

I evaporate 7 L/hr over 90 min with a converted keg an a 25cm hole in the top. This is with the boil as vigorous as possible with out getting a boil over. Im interested to know what the evaporation rate is with the entire top cut off the keg and if it would be worth doing?


----------



## Tony (16/7/07)

yeah my %age is calculated on a 9 liter loss over 1 hour. I just worked out the %age for this post.

I only ever go by evap rate.... not % for the reason andrew raised.

If i make a 45 liter batch compared to a 55 liter batch i usually do, the calculation on percentage will be wrong by 1 or 2 liters. I will still get the same 9 liter boil off.

cheers


----------



## RobW (16/7/07)

The other thing that affects evaporation rate is draughts & wind. If you boil outside on a windy day there's a significant increase in boiloff. Same goes for garages/sheds where you might have the door & the window open to clear the steam.


----------



## Ross (16/7/07)

RobW said:


> The other thing that affects evaporation rate is draughts & wind. If you boil outside on a windy day there's a significant increase in boiloff. Same goes for garages/sheds where you might have the door & the window open to clear the steam.



Really :blink: , I actually get the opposite - The wind affects the flame under the kettle & it doesn't boil as vigourously, a real problem for me on a windy day.

cheers Ross


----------



## Maxt (16/7/07)

I lose about 12L in a 35L boil 80L kettle over 90mins


----------



## Steve (16/7/07)

Maxt said:


> I lose about 12L in a 35L boil 80L kettle over 90mins




:blink: 12 litres!

I lose 5L in a 26-27L boil, 50 litre kettle over 60 mins....not good at maths so cant work out percentages :lol: 
Cheers
Steve


----------



## therook (16/7/07)

Steve said:


> :blink: 12 litres!
> 
> I lose 5L in a 26-27L boil, 50 litre kettle over 60 mins....not good at maths so cant work out percentages :lol:
> Cheers
> Steve




Thats about 19%


----------



## Cortez The Killer (16/7/07)

I just recalculated my boil off rates for my batches to date and it seems that I'm getting a touch over 4 litres per hour (I usually boil for 75 mins) 

I've had a hell of a time applying a percentage in the past to the boil off amount as a percentage, as it would always change. This appears to be exacerbated by my changing batch size.

I'll stick with 4 litres per hour moving forward I think

Cheers


----------



## RobW (17/7/07)

Ross said:


> Really :blink: , I actually get the opposite - The wind affects the flame under the kettle & it doesn't boil as vigourously, a real problem for me on a windy day.
> 
> cheers Ross



Never had a problem with the burner Ross but I haven't brewed on a really windy day, just noticed that when there's a bit of a breeze I get a bigger boiloff - strictly qualitative observation I should add. 

Do you have a shield around your burner?


----------



## TidalPete (17/7/07)

Maxt said:


> I lose about 12L in a 35L boil 80L kettle over 90mins



I lose 7+ litres per 35 litre rolling boil in a 70 litre stockpot (450mm dia) over 90 minutes using a NASA. 

:beer:


----------



## Ross (17/7/07)

RobW said:


> Never had a problem with the burner Ross but I haven't brewed on a really windy day, just noticed that when there's a bit of a breeze I get a bigger boiloff - strictly qualitative observation I should add.
> 
> Do you have a shield around your burner?



No shield, as I'm in a fairly protected spot under the verandah, but with the burner turned down low once the boil starts, any breeze makes a big difference.
Not doubting your observations, but intrigued how a breeze gives you a significant increase in boiloff.

Cheers Ross


----------



## Cortez The Killer (17/7/07)

I've wondered if the presence of a jumbo hop bag affects evaporation

I have a converted keg kettle and with the hop sock in there there is not a terrible amount of room (I'm thinking about increasing the size of the hole).

Would the sock interfer with the evaporation and make it condense again and fall back into the kettle?

Here's a pic of the kettle - is the hole big enough to achieve sufficient boil off?








Cheers


----------



## braufrau (17/7/07)

Ross said:


> No shield, as I'm in a fairly protected spot under the verandah, but with the burner turned down low once the boil starts, any breeze makes a big difference.
> Not doubting your observations, but intrigued how a breeze gives you a significant increase in boiloff.
> 
> Cheers Ross




This is bit OT but I was pondering the logistics of AG the other day and thinking what do the outdoors guy do if, say, an autumn leaf lands in the kettle! :unsure:


----------



## tangent (17/7/07)

don't boil under a tree
nothing on the leaf will last longer than a few seconds


----------



## RobW (17/7/07)

Ross said:


> No shield, as I'm in a fairly protected spot under the verandah, but with the burner turned down low once the boil starts, any breeze makes a big difference.
> Not doubting your observations, but intrigued how a breeze gives you a significant increase in boiloff.
> 
> Cheers Ross



I assume from increased evaporation - the same reason washing dries faster on a windy day.


----------



## BrotherNutz (17/7/07)

I worked out the evap based on 4.8KW over 1 hour. Came out to 8 liters. As it happens, that is just what I get!  

Heat source is two 2.4KW immersion heaters. Boiler is an old 50L keg.


----------



## Guest Lurker (17/7/07)

Ross said:


> Not doubting your observations, but intrigued how a breeze gives you a significant increase in boiloff.
> 
> Cheers Ross



As the water evaporates, it starts to saturate the air sitting above the kettle to the point where it cant take any more water vapour. The faster you blow away the "wet" air above the kettle, and replace it with "less wet" air, the more evaporation can occur, assuming everything else stays the same. Haven't tried it, but supposedly for a barley wine to get extra evap you can point a fan at the top of the kettle.


----------



## BrotherNutz (17/7/07)

Guest Lurker said:


> As the water evaporates, it starts to saturate the air sitting above the kettle to the point where it cant take any more water vapour. The faster you blow away the "wet" air above the kettle, and replace it with "less wet" air, the more evaporation can occur, assuming everything else stays the same. Haven't tried it, but supposedly for a barley wine to get extra evap you can point a fan at the top of the kettle.



That doesn't sound like solid science there....

If I am applying X amount of power to the boil, it will seek to go no higher than 100degC (ignoring altittude adjustments) regardless of any extra power I add to it. It will simply boil faster, and evap more. The energy applied needs to go somewhere. If it can't dissipate, the boiler will build up pressure and THEN the temp of the boil can go past 100.

If evap were constrained in some way by the 'air' above the boil, either the pressure or the temperature of the boil would have to rise. And I think you would agree that that is highly unlikely.


----------



## RobW (17/7/07)

BrotherNutz said:


> That doesn't sound like solid science there....
> 
> If I am applying X amount of power to the boil, it will seek to go no higher than 100degC (ignoring altittude adjustments) regardless of any extra power I add to it. It will simply boil faster, and evap more. The energy applied needs to go somewhere. If it can't dissipate, the boiler will build up pressure and THEN the temp of the boil can go past 100.
> 
> If evap were constrained in some way by the 'air' above the boil, either the pressure or the temperature of the boil would have to rise. And I think you would agree that that is highly unlikely.



The issue isn't about how much power goes into the boil. If you leave a keg of water for long enough at any temperature you will get evaporation. It's about removing moisture laden air from the liquid/air interface and replacing it with "dry" air that can take up more water. The more "dry" air you blow over the liquid/air interface the quicker the liquid evaporates. The evap rate in still air is the baseline and by increasing the air movement you increase the evap rate (all other factors being equal).


----------



## andreic (17/7/07)

Hi,

I have a 60L aluminium pot and a HP wok burner. I've only done 9 brews but I now generally aim for a 90min boil, starting at 34-35L and ending at 24-26L. Recently I've had a few odd results. On a few occasions I have ended up with much lower evaporation rates. One time I ended up with around 28L, the other time I boiled real hard for the last 45 mins, extended my boil time and just made it down to 26L. I am a night brewer outdoors in Melbourne... I think the nights in question were rather cold, and one was a bit wet, so I may boil longer or start with a lower volume for my next few brews.

I am now trying to take more detailed notes to see if I can get a bit more consistency in future.

Andrei


----------



## PistolPatch (17/7/07)

TidalPete said:


> I lose 7+ litres per 35 litre rolling boil in a 70 litre stockpot (450mm dia) over 90 minutes using a NASA.
> 
> :beer:



I've got to the stage where any threads involving measurements scare me :unsure: 

A few months ago we had an intersesting discussion on evaporation rates in the BIAB thread. Thirsty gave some good reasons to not boil too vigorously.

After that I attempted to get my evaporation rate down. No matter what I did, I found it impossible to get down to 15%. I tried lid mostly on, reduced flame etc but I'm still up around matti's results. I lose around 10 litres in a 60 minute boil. It's got me buggered as TidalPete and I have exactly the same pot :blink:

I'm starting to shy away from doing too much measuring now - too depressing!
Pat


----------



## sinkas (18/7/07)

Just to change the perspective, I always thought that one of the reasons for open boiling was to boil off, off flavours, impurities, etc, so I wonder why I am hearing about peoples "Lids half on" boils, is it not defeating much of the reason for boiling?


----------



## Thirsty Boy (18/7/07)

I boil off 12-15% of my starting volume. Yes, I use the % figure and I actually change my setup (flame level, lid, pot size etc etc) to make sure that I fall in that range.

People constantly misunderstand what the % figure of boil off is for... its not really about how much you boil off in an hour, the figure is a tool for expressing the *level of vigor* in your boil.

If you are boiling off somewhere in the vicinity of 12-15% per hour, your boil is vigorous enough to do everything that its supposed to do, but its not so vigorous that you might be in danger of suffering some of the possible negative effects of boiling too hard. This is independent of the volume of your boil.

if you are always doing roughly the same batch size... then it just doesn't matter if you express your boil off as a percentage or a Litres/hour figure, but if you significantly vary your batch size then it will.

eg: I start with 22.5litres looking for 15% per hour (19into fermentor) and I boil off 3.4litres. Great, every time I do a batch I can just use 3.4ltres per hour... right?? Same pot, same burner settings.

Except when I do an 10 litre batch, then even if the rate was the same (it isn't) then I lose nearly 40% of my volume. The boil goes apeshit and is obviously far to "hot"

Conversely, if I do a 45lire boil volume, the same level of heat hardly makes the boil come to the surface, it barely ticks over! I'm probably still getting about 3.4litres per hour, but the boil is patently not "hot" enough.

Its obvious really, same energy in, same kettle geometry... changing the volume is going to change the vigor/hardness/anger/heat/level whatever you want to call it, of the boil.

But you dont want the vigour of the boil to be random, or variable depending on your batch size, you want it to be what you planned it to be... which is where the % figure comes in.

15% of 10 litres is 1.5lires/hour - a nice gentle rolling boil..
15% of 22 litrs is 3.4lires/hour - a nice gentle rolling boil..
15% of 45 litres is 6.75litres/hour - a nice gentle rolling boil..

Thats what the percentage figure is for. People who say that it is pointless or a waste of time, are usually applying the figure in a way that isn't really its purpose.

And *Jeezus H Christ* do people really boil off at 25% per hour?? bloody hell !! what for?? hell guys, the pro's/micros are going with something around 8% and the megas are doing closer to 4%... That high a rate just isn't needed; and it might be doing your beer a bit of no good.

Save yourself some money and turn the gas down a bit... sheesh


----------



## AndrewQLD (18/7/07)

The purpose of a boil off rate is to aid in calculating final volumes in the boiler, using lt/hr rate I don't have to adjust my boil rate/vigour to come up with the same figure, I know I get 6lt evaporation everytime. Very simple and straight forward. I think the % rate is really for people that brew the same volume constantly and just makes the calculations more complex for those that brew varying sized batches.



> But you dont want the vigour of the boil to be random, or variable depending on your batch size, you want it to be what you planned it to be... which is where the % figure comes in.
> 
> 15% of 10 litres is 1.5lires/hour - a nice gentle rolling boil..
> 15% of 22 litrs is 3.4lires/hour - a nice gentle rolling boil..
> 15% of 45 litres is 6.75litres/hour - a nice gentle rolling boil..



I may have misunderstood the above comments but it seems you have contradicted yourself here. It looks to me like you Will have to vary the boil vigour based on your figures above in order to achieve the same evaporation amounts.

Cheers
Andrew


----------



## warrenlw63 (18/7/07)

Guest Lurker said:


> As the water evaporates, it starts to saturate the air sitting above the kettle to the point where it cant take any more water vapour. The faster you blow away the "wet" air above the kettle, and replace it with "less wet" air, the more evaporation can occur, assuming everything else stays the same. Haven't tried it, but supposedly for a barley wine to get extra evap you can point a fan at the top of the kettle.






RobW said:


> The issue isn't about how much power goes into the boil. If you leave a keg of water for long enough at any temperature you will get evaporation. It's about removing moisture laden air from the liquid/air interface and replacing it with "dry" air that can take up more water. The more "dry" air you blow over the liquid/air interface the quicker the liquid evaporates. The evap rate in still air is the baseline and by increasing the air movement you increase the evap rate (all other factors being equal).



So in layman's terms all that's occuring is a scaled down version of what creates rain I suppose? :blink: 

Bulk buy for barometers anybody?  

Warren -


----------



## BrotherNutz (18/7/07)

RobW said:


> The issue isn't about how much power goes into the boil. If you leave a keg of water for long enough at any temperature you will get evaporation. It's about removing moisture laden air from the liquid/air interface and replacing it with "dry" air that can take up more water. The more "dry" air you blow over the liquid/air interface the quicker the liquid evaporates. The evap rate in still air is the baseline and by increasing the air movement you increase the evap rate (all other factors being equal).



Yep, I agree with that contention, but you are now talking about a natural evaporation rate versus a forced phase change to a gas under huge amounts of applied energy.

*"The issue isn't about how much power goes into the boil"*

Yes, this does matter. I can boil with one element, or I can boil with two. My evap rate using maths alone is halved. In practice this is not the case due to energy lost through radiated heat etc.

*"It's about removing moisture laden air from the liquid/air interface and replacing it with "dry" air that can take up more water"*

The air is not moisture laden. Steam is a gas, not a liquid. Once the gas condenses, then it is a liquid/visible moisture.

Yes, I agree that if one blows air over a body of water for a couple of weeks, one will get more evaporation than the same body of water in still air. Air temp and humidity all being equal. However, we are not talking about boiling for weeks! We are talking about 60 to 90 min boils here.

Basically it comes down to this, know what your evap rate is and use these figures in ProMash and ye will be a happy beer brewer! :chug: :beer:


----------



## fraser_john (18/7/07)

Last night I conducted an experiment, I added 32 litres of water to my kettle and boiled it, fairly vigorously, but not too hard. It was 4 degrees outside and I had a fan extracting the moist air outside very rapidly.

After 30 minutes of boiling, I chilled it and measured what I had left over. 27.5 litres (including what was left in the kettle).

Giving a loss rate of 9 litres/hour or 28% !!!!! Cripes! But, given this is only over a 32 litre starting volume. Assume that the loss rate is the same and I started with a 48 litre wort it would still result in an 18.75% boil off rate. Given some of the discussion in this thread, that is still very high!

Now, does pure water evaporate out of a boil faster than when a wort is boiled? I cannot imagine that it would be that much different? What about the head space left in a kettle whilst boiling, does that affect the rate?

Maybe it was my rapid movement of air across the top of the kettle and the low temperature that helped leach away the vapor?

I dunno, but I am still going to be struggling with how to get consistent end wort sizes into my ferment unless I get my kettle figured out :angry:


----------



## Tony (18/7/07)

PistolPatch said:


> When we start out AGing*, every measurement we hear about seems really important. From what I have brewed or the beers I have tasted that others have brewed, none of these measurements are critical. Some people make them sound critical but they are not.
> 
> 
> If you have a good thermometer and a good recipe (a good grain and hop bill) you should feel really confident in those and not worry too much about meaurements especially if you start low-tech. You might end up with a little more wort than you can fit in your fermenter. So what? Chuck it out. It's only a dollar or two of ingredients. You might end up with less than will go in your fermenter. Top it up with tap water.
> ...



Pat Pat......... that was poetry.

And SOOOOOOOOO true :super: 

All new AG'ers read these three phrases and memorise them!

I will add 1 more very critical item to good beer. Fermentation Temperature!

Now back on track....... All i did with my new kettle when i first started was what Pat just said. I didnt wory about the amounts too much. I actually worked it to undershoot the target volume cause you can just top it up with water to what it would have been if i got it right so who cares. You top a kit up from the tap dont you? I always did.

I worked on a starting number of 3 liters/hr from memory.

I measured the volume in the kettle with pre-marked stick in liters and then measured it when i shut off the burner after 60 minuites. 

I measured 4 or 5 liters gone from memmory so my brew came out at 21 liters instead of 23. I fired up the hose and what do you know, back to what it should be.

These days i tend to deliberatly under shoot. 50 liter batches are heavy and a 45 liter batch is easier to lift. So with my system, i just fill the MT to the top with sparge water ( i dont measure it, i just pump it in till its full) stir it, recirc till claer and pump it in.

Sometimes it comes in close, sometines im 5 liters short but who cares. When i run it into the keg, i top it up with a few liters and its back to what it should be.

cheers


----------



## SpillsMostOfIt (18/7/07)

Tony said:


> So with my system, i just fill the MT to the top with sparge water ( i dont measure it, i just pump it in till its full) stir it, recirc till claer and pump it in.



In my 75litre boiler, my measurements tend to be along the lines of '22cm into boiler'. I don't know what the actual volume of that is - the shape is a bit wonky, so trying would be pointless. I sparge with '15cm into big saucepan'. I end up with enough to fill a 20 (24litre) jerry, which becomes 23litres in fermenter.

Disgustingly unscientific, but it works!

I'm running in a very small batch kit, which I fire on the stove and am trying to do the same thing. The height measurements don't add up and I figure I might have to throw more science at it... *sigh*


----------



## PistolPatch (18/7/07)

Tony said:


> Pat Pat......... that was poetry.



LOL Tony! While you were writing your post I was doing a very heavy edit on mine. I just deleted all the stuff you quoted!!! Good to see some of it made sense :beerbang: 

Spot from Pat Pat


----------



## warra48 (18/8/07)

I venture to think that the humidity of your brewing environment will also have an impact on the rate of evaporation. The measured humidity in my home area is rarely less than 70% and often over 80%. Hence the capacity of the air to absorb more moisture is much less than say over in the Western Australia where the humidity is much lower. Then it must also be affected by the ambient air temperature, as cold air saturates at lower levels of moisture then warmer air.
I just stick with brewing all my batches to the same volume, and trust that my measurements remain fairly constant.


----------



## LovesToBrew (18/8/07)

i like to work off a litre amount rather than %, i find i evaporate teh same amount whether my 70litre robinox is at 30 litres or 60 litres


----------



## mudsta (18/8/07)

Ive got two different size elements in my setup.
I switch on both to bring to the boil and switch one off after hotbreak.

I use promash and keep my boils generally the same length of 75mins.
My boil off rate is 11.6%/hr with the one element going. Generally with the cals done at the start of boil I get within 500ml accuracy at the end of boil.

I'm about to upgrade to a new setup with gas heating and presume the accuracy will be less consistent.

I read somewhere a while back that commercial setups evap rate is in the range of 5 - 10%/Hr, thats why I only use one element instead of two (two puts me into the 26%/hr range)

Mudsta :beerbang:


----------



## LovesToBrew (18/8/07)

that would give good control mudsta, i'm still trying to find a consistent settign with the gas burner


----------



## MHB (18/8/07)

Boiling is a fascinating part of wort production - the evaporation rate is an important part of the process, but the one question that isnt being asked is "Why do the textbooks say we should be getting that 8-10% evaporation".

Primarily it's to remove Undesirable Hop Volatiles; if you achieve 8-10% loss as vapour you can be assured that the hop fractions you dont want in your beer will have been ejected.

Evaporation rates higher than 10% would serve no beneficial purpose and could have drawbacks, like accelerated darkening of the wort and excessive protein degradation.
They also consume more energy ($) and create a lot of steam that has to be dealt with.

Unless you are trying to make a very high gravity beer or are using monumental amounts of hops, enough heat to do the job is all you need.

From the above it is easy to understand why texts express the evaporation rate as a percentage.

Further on the moving air question:-
Vapour as it leaves the surface has just enough energy to undergo a phase change (liquid to gas). As the concentration of vapour in the atmosphere builds up, at some point it becomes supercritical (saturated) and a large portion of the vapour condenses and falls back into the kettle.

As we are trying to get rid of the hop volatiles (not the water) preventing the moisture concentration in the atmosphere above the surface from saturating will encourage the volatiles to leave and not be returned to the kettle with water vapour that is recondensing (i.e. when it does recondense it isnt over the kettle).

So yes a fan, draft or even a chimney can all help the evaporation rate.

MHB

PS
Why do paint drops dry as little circles, it is actually related.
Mark


----------



## braufrau (18/8/07)

mudsta said:


> Ive got two different size elements in my setup.
> I switch on both to bring to the boil and switch one off after hotbreak.



that's what I do too now.
There's so much hoo hah in internet land about hot break and the importance of
a rolling boil that I was boiling on two burners full bore for an hour and losing .... wait for it ...
50% of my wort! 
That didn't seem right! :blink: 
Don't know what it is now, but it looks about 15% and I feel much happier now and that's the main thing.


----------



## mika (18/8/07)

Ding Ding ! We have a winner !

50% of your wort...I'd like to see that burner and that much steam ! :beerbang:


----------



## mudsta (19/8/07)

The main reason for a massive boil off rate (i.e. heat input) is to clone the malliard reaction. Which trys to clone decoction mashing to a degree.

Bluntly, more browing of the sugars. See the master George Fix's books for this info.

The more water used in mashing just dilutes the end product and adds more energy expense in the boil.
We do need to boil to sterilize and drive off the nasties but their is a limit. 50% WOW!! that is beyond extreme.

Mudsta :beerbang:


----------



## Thirsty Boy (20/8/07)

AndrewQLD said:


> The purpose of a boil off rate is to aid in calculating final volumes in the boiler, using lt/hr rate I don't have to adjust my boil rate/vigour to come up with the same figure, I know I get 6lt evaporation everytime. Very simple and straight forward. I think the % rate is really for people that brew the same volume constantly and just makes the calculations more complex for those that brew varying sized batches.
> I may have misunderstood the above comments but it seems you have contradicted yourself here. It looks to me like you Will have to vary the boil vigour based on your figures above in order to achieve the same evaporation amounts.
> 
> Cheers
> Andrew




Sorry for the late reply to this Andrew, I hadn't seen your comment.

Yes, I think you have misunderstood. Almost completely I'm afraid.

I wouldn't be changing the boil vigor to achieve the same evaporation amounts. I would be _changing the evaporation amounts_ (in litres per hour) in order to achieve the same level of vigor. This would give me a consistent evaporation rate expressed as a %

I do this by varying the amount of heat I apply to the kettle, perhaps putting a lid half on the kettle or by changing to a different kettle for very small batches, or some combination of the above.

And therefore (including reasons from my earlier post) I think exactly the opposite to you about the % figure. Boil of rate (%) isn't about calculating pre & post boil volumes, its about knowing that your boil is at the appropriate level of vigor and its mainly useful if you DO change your volumes significantly from brew to brew... If you are brewing roughly the same sized brew every time, then you just need to check it and play with your set-up till you have it in a reasonable range, then you can stop worrying about % and just calculate the L/hr figure that you always get.

Let me pose you a question.... You say that you get 6litres per hour everytime. What would you do if I asked you to brew me a 6 litre batch of beer?? Would you simply aim for a pre-boil volume of 12 litres and boil away half the wort? (braufrau might  )

OR

Would you rightly think that doing that may well adversely effect the quality of the beer, and decide to change your pot/burner settings/lid/ etc etc so you could boil off less. How much less?? How much should you aim for??

Thats where the % figure comes in... I'd aim for 15% of the starting volume. I want to finish with 6litres, so that means a pre-boil volume of 7litres. So now I know that I need to fiddle with my system to the point where I get 1 L/hr boil off.


Now, brew me 500litres... still going to go with 1 l/hr ... of course not, how about 6... still probably not... but 15% = 88litres makes a bit more sense

See what I mean?

Thirsty


----------



## Screwtop (20/8/07)

Thirsty Boy said:


> Sorry for the late reply to this Andrew, I hadn't seen your comment.
> 
> Yes, I think you have misunderstood. Almost completely I'm afraid.
> 
> ...




Thirsty it's all related to scale and economy of scale in brewing is no different. If the whole system were scaled up or down to suit the nominated value of wort then all things would be equal would they not. If I boiled a small batch in my boiler I would not achieve the 15.5% that I always get with a 32.25L (pre-boil) batch. Percentages should work fine irregardless of scale but in the physical world (read physics) many other variable come into play, fixed math principals apply at a much more basic level. Greater than 10% boiloff in a 200CL kettle to ensure removal of undesirable Hop Volatiles or for Malliard reactions or for whatever reason is far different to what percentage may be required to achieve the same desired result using a 50L kettle. But that shit's far too deep, lighten up I say.

How about this.

3 guys pitched in $10 each to buy a $30 carton at the bottlo. They'd just walked out as the manager advised staff that the cartons had been dropped by $5 for an hour as a promo special, go and give them $5 back he said. Well the staffer thinks dividing $5 between three is too hard and sees a way to make a couple of bucks, so pockets $2. Outside the bottlo he apologises and says the cartons were on a quickie special giving each of them $1. They were surprised at the honesty and went away happily to be repeat customers of that business. But how much did they pay for the carton, originally $10 each then they each received a refund of $1 so they paid $9 each that's $27 add back the $2 pocketed by the sales person and the total is $29 so where did the other dollar go. Must have miscalculated the % loss  

BF: I don't think I could boil hard enough to achieve 50% loss, well maybe I could, but I'd end up mopping most of it up off the floor after the boil over.


----------



## ozpowell (20/8/07)

Thirsty Boy said:


> I wouldn't be changing the boil vigor to achieve the same evaporation amounts. I would be _changing the evaporation amounts_ (in litres per hour) in order to achieve the same level of vigor. This would give me a consistent evaporation rate expressed as a %



Thanks for conveying this so succinctly Thirsty! Makes perfect sense to me now - scary :blink: 

I've been struggling with this exact question recently as I'm about to do my first half batch.

Cheers,
Michael


----------



## AndrewQLD (20/8/07)

> I wouldn't be changing the boil vigor to achieve the same evaporation amounts. I would be changing the evaporation amounts (in litres per hour) in order to achieve the same level of vigor. This would give me a consistent evaporation rate expressed as a %


I'm not sure if I follow this at all, wouldn't changing the amount of heat also change the boil vigor?



> I do this by varying the amount of heat I apply to the kettle, perhaps putting a lid half on the kettle or by changing to a different kettle for very small batches, or some combination of the above.


And that is my point, if you do a 24 lt boil and a 30 lt boil you will have to stuff around getting a lid on the boiler in the right spot or the flame on your gas at the right level or heaven forbid a different size pot so you can get your percentage figures the same for both batches. I don't need to do any of that.

I tend to go about it differently,
I don't put a lid on the kettle.
I don't adjust my burner/ boil vigor.
I don't change pot size.

I rate my boil off as lt/hour because that is a constant figure of six lt. If I boil 24 lt or 30 lt it is still 6lt/hour.
And that is how I like it easy and simple, I know exactly how much wort I need preboil and exactly how much I will get post boil because my evaporation rate is a constant 6lt per hour.

I can see what you mean as far as percentages are concerned and smaller batches ie 6lt, but that would be totally inapplicable to me and so I don't worry about it. 

Thirsty, your method/system works for you just as well as mine works for me, but I prefer mine for it's simplicity.

Cheers
Andrew


----------



## ozpowell (20/8/07)

AndrewQLD said:


> I'm not sure if I follow this at all, wouldn't changing the amount of heat also change the boil vigor?



Hey Andrew,

I think Thirsty's point (or at least the way I understand it) is that for different boil volumes, you need different amounts of energy to maintain the same level of boil vigor. And a constant boil vigor == a constant % evaporation.

Seems to make some sense to me (Disclamer - I'm a software engineer, not a physicist, so I could be totally wrong  )

Cheers,
Michael


----------



## AndrewQLD (20/8/07)

ozpowell said:


> Hey Andrew,
> 
> I think Thirsty's point (or at least the way I understand it) is that for different boil volumes, you need different amounts of energy to maintain the same level of boil vigor. And a constant boil vigor == a constant % evaporation.
> 
> ...



Hi Michael,
But I don't see that on my system though, 2 ring burner flat out gives me 6lt evaporation from a 20lt or 40lt of wort. Perhaps this is a system/equipment specific thing, either way it doesn't really matter so long as you get the results you want.  

Cheers
Andrew


----------



## ozpowell (20/8/07)

AndrewQLD said:


> Hi Michael,
> But I don't see that on my system though, 2 ring burner flat out gives me 6lt evaporation from a 20lt or 40lt of wort. Perhaps this is a system/equipment specific thing, either way it doesn't really matter so long as you get the results you want.
> 
> Cheers
> Andrew



I'm going to do a half batch soon on my equipment, so I'll update with my results....

Cheers,
Michael


----------



## Sammus (20/8/07)

Screwtop said:


> How about this.
> 
> 3 guys pitched in $10 each to buy a $30 carton at the bottlo. They'd just walked out as the manager advised staff that the cartons had been dropped by $5 for an hour as a promo special, go and give them $5 back he said. Well the staffer thinks dividing $5 between three is too hard and sees a way to make a couple of bucks, so pockets $2. Outside the bottlo he apologises and says the cartons were on a quickie special giving each of them $1. They were surprised at the honesty and went away happily to be repeat customers of that business. But how much did they pay for the carton, originally $10 each then they each received a refund of $1 so they paid $9 each that's $27 add back the $2 pocketed by the sales person and the total is $29 so where did the other dollar go. Must have miscalculated the % loss



hehe the maths is all wrong here. It's good food for thought though. Upon close inspection your just basically adding/taking away any old number that came up in the story.


----------



## Sammus (20/8/07)

AndrewQLD said:


> Hi Michael,
> But I don't see that on my system though, 2 ring burner flat out gives me 6lt evaporation from a 20lt or 40lt of wort. Perhaps this is a system/equipment specific thing, either way it doesn't really matter so long as you get the results you want.
> 
> Cheers
> Andrew



maybe your burner is only capable of putting in so much energy, and that limit peaked at your 20L batch. You need a certain % evaporation to get rid of certain hop volatiles and whatnot. given that you've met and exceeded those values, the rest is just a waste of energy. The point is you could turn your burner way down for your 20L batch and still observe the required evaporation (ie to get rid of hop volatiles and whatever, no for beersmith to calculate your efficiency )


----------



## ozpowell (20/8/07)

Well wadda ya know. Here I am reading my latest BYO mag and what do you think this edition's Advanced Brewing topic is? A discussion of aspects of wort boiling.... Here's a few quotes that I think add an interesting twist to this discussion:


> The amount of evaporation varies with the size and geometry of the kettle, the surface area exposed to the air, the intensity of the heat source and to a lesser extent other variables such as the ambient temperature, humidity, air pressure and any movement of are surrounding the kettle.


and


> For homebrew size batches (5 - 15 gallons/19-57L), the evaporation rate is normally measured in gallons (or liters) per hour, with typical values of 1 to 1.5 gallons (3.8 to 5.7 L) per hour.
> ...
> Measure the volume both at the beginning and end of the boil and calculate the difference. Divide by the boiling timein hours to determine the evaporation rate.
> 
> ...


Finally, in relation to boiling the wort covered vs. uncovered:


> ...
> DMS is undesirable in nearly all beer styles. Fortunately, DMS is volatile, and a vigorous boil evaporates it and drives it off into the air with the steam. ... For this reason it's important to leave the kettle mostly uncovered during the boil so the steam does not condense and return to the wort.



:blink: 

Cheers,
Michael


----------



## Tony (20/8/07)

exactly !

cheers


----------



## Screwtop (20/8/07)

Sammus said:


> hehe the maths is all wrong here. It's good food for thought though. Upon close inspection your just basically adding/taking away any old number that came up in the story.




Well, how much each did they pay?


----------



## Sammus (20/8/07)

Screwtop said:


> Well, how much each did they pay?



They still effectively paid $9 each. The problem is the "add $2 the sales guy took" Now why would you do that? that $2 he took essentially increases the price of the case to $27, and it all works out fine and dandy. That is, the fact the refund was only $3 (as opposed to $5) already took into account that the clerk stole $2 (ie added $2 to the actual cost of the case, making it $27) Theres no reason to add it on again!


----------



## kook (20/8/07)

Thirsty Boy said:


> I wouldn't be changing the boil vigor to achieve the same evaporation amounts. I would be _changing the evaporation amounts_ (in litres per hour) in order to achieve the same level of vigor. This would give me a consistent evaporation rate expressed as a %
> 
> I do this by varying the amount of heat I apply to the kettle, perhaps putting a lid half on the kettle or by changing to a different kettle for very small batches, or some combination of the above.



So say you've got a 98L kettle, and you're switching from a 60L batch to a 30L batch. Would you just gently simmer the 30L batch (so as to achieve the same evaporation percentage)?

Will the gentle simmering still cause enough break up of proteins etc as opposed to using a rolling boil? Doesn't it also help with hop isomerisation?

I realise that commercial breweries acheive a much lower boiloff (percentage wise), but most of their kettles are shaped to promote a continual, rolling boil.

Am I confused, or are you saying that it is much better to have a gentle, simmering boil (to reduce evaporation rates) rather than a rolling boil, as if the evaporation is exceeeding 15% you may have excessive maillard reactions?



edit - I've just re-read everything you've said, and I'm even more confused. It makes perfect sense if you're changing kettles for different sized batches (ie, wort surface area changes), but otherwise other than reducing the heat, how can you still acheive a rolling boil while maintaining a steady evaporation percentage?


----------



## Screwtop (20/8/07)

Sammus said:


> They still effectively paid $9 each. The problem is the "add $2 the sales guy took" Now why would you do that? that $2 he took essentially increases the price of the case to $27, and it all works out fine and dandy. That is, the fact the refund was only $3 (as opposed to $5) already took into account that the clerk stole $2 (ie added $2 to the actual cost of the case, making it $27) Theres no reason to add it on again!




They Paid $30 ($10 ea) refund $5 ($2 for the salesman and $3 for the boys) so they paid $9 each = $27 and the $2 for the salesman = $29 your math is all wrong


----------



## Sammus (20/8/07)

Screwtop said:


> They Paid $30 ($10 ea) refund $5 ($2 for the salesman and $3 for the boys) so they paid $9 each = $27 and the $2 for the salesman = $29 your math is all wrong



I guess its a good exercise in logic if you haven't spent the past 6 years studying these kinds of problems... But believe me when I say this argument has a major flaw in it - the point where you add $2 of the refund onto the total amount paid, instead of taking it away like you do with $3 part. Now go and think about it a bit more - act it out with 3 friends if you want. Maybe then you can realise that people who research maths for a living don't tend to trip up on these often encountered logical paradoxes (I've seen it a several times before in different forms, I think it originated with people paying for a hotel room or something).

Think about it, you start with $30 thrown in. Then theres a $5 refund given. Why do you subtract 3 of those $5 from the $30, and add the other two?

Either keep track of all the money properly: subtract the whole five and end up with $25 to the boss, $2 to the sales clerk, and $3 to the customers.

Or you can look at from the sales clerks perspective: He gave them $3 change from $30, essentially charging them $27, which is $2 more than he needed to put in the till, so $25 in the till, $2 in his pocket. Still ends up being $25 = $30 - ($3 + $2) (Cost = Total - Refund).

Or you can look at it from my point of view: Hey look these 3 guys just paid $27 for a $25 case of beer, I wonder that extra $2 went that they paid? Oh it went to the slack ass sales clerk. Still ends up making sense.

Edit: I just realised you may be taking the piss out of me... I neglected to think about the "mustve miscalculated the % loss" statement that means u probably already know the solution... <_<


----------



## Screwtop (21/8/07)

Sammus said:


> I guess its a good exercise in logic if you haven't spent the past 6 years studying these kinds of problems... But believe me when I say this argument has a major flaw in it - the point where you add $2 of the refund onto the total amount paid, instead of taking it away like you do with $3 part. Now go and think about it a bit more - act it out with 3 friends if you want. Maybe then you can realise that people who research maths for a living don't tend to trip up on these often encountered logical paradoxes (I've seen it a several times before in different forms, I think it originated with people paying for a hotel room or something).
> 
> Think about it, you start with $30 thrown in. Then theres a $5 refund given. Why do you subtract 3 of those $5 from the $30, and add the other two?
> 
> ...



:lol: no harm just fun intended Sammus, love to see simplicity explained in detail :lol: 

But you can't deny the guys paid $27 for a carton of beer and the salesman got $2 thats $29. How, when the whole original $30 transaction consisted of $25 + $5 discount.


----------



## Sammus (21/8/07)

Screwtop said:


> :lol: no harm just fun intended Sammus, love to see simplicity explained in detail :lol:
> 
> But you can't deny the guys paid $27 for a carton of beer and the salesman got $2 thats $29. How, when the whole original $30 transaction consisted of $25 + $5 discount.



No denying your arithmetic is perfect, 27 + 2 = 29, no doubt in my mind there. And yeah, the guys paid $27 for a carton of beer, and the salesman got $2. It was not an extra $2 on top of the $27 though, it was part of the $27 in the first place.

I'm over it anyway lol


----------



## Sammus (21/8/07)

Anyway, I digress!!  (sorry people who didn't find it amusing )

My kettle evaporation rate is close to 20%, I can't get it lower unless I turn the burner down so low it ain't boiling anymore!


----------



## Screwtop (21/8/07)

Sammus said:


> Anyway, I digress!!  (sorry people who didn't find it amusing )
> 
> My kettle evaporation rate is close to 20%, I can't get it lower unless I turn the burner down so low it ain't boiling anymore!




On Ya Sammus  enjoyed the joust. You must have a full opening on your kettle, yes? 

I pretty much get 15.5% on 32.25L pre boil volume, depends on how hard I can get it boiling, some worts will froth and boil over more easily than others. Use a keg style boiler here with a 24cm hole in the top.

Screwy


----------



## Thirsty Boy (21/8/07)

kook said:


> So say you've got a 98L kettle, and you're switching from a 60L batch to a 30L batch. Would you just gently simmer the 30L batch (so as to achieve the same evaporation percentage)?
> 
> Will the gentle simmering still cause enough break up of proteins etc as opposed to using a rolling boil? Doesn't it also help with hop isomerisation?
> 
> ...




The notion that the evaporation rate is independent of energy applied & the volume of liquid and dependent only on the surface area, is as far as I am concerned, based on the notion that your heat source is running flat out.. you are using a non adjustable electric element, or something like a turkey burner where its either all guns blazing, or nothing. If you have the capacity to put into the system, much more or much less energy than required to bring the volume to the boil, then that assumption no longer holds true.

For example: I can tell you for sure, that I get a MUCH higher evaporation rate out of my small kettle when its on my three ring burner, than I do when its on my stove... it geometry is the same and so is its surface area... so it must be the energy source.

When you increase volume, its more about the vertical height than volume I suppose, the heat and bubbles of steam lose energy to the liquid as they make their way to the top and the boil may not break the surface, So you have to shove in more heat to get the "vigor" up to a good level. So when you reduce from (in your example) 60l to 30l there is half the vertical distance, the heat can be turned down, the percentages will be roughly maintained and so will the vigor.

Thats the whole point... its *not* about maintaining a % figure.. let me emphasize... * not about the figure* ...its ALL about the vigor of the boil. The percentage figure is only a tool, that gives you a reasonable measurement of the vigor of the boil.. independent of the volume.

I keep repeating this sort of example.. I cant see how it is confusing

15% of 10litres is 1.5litres --- which is a nice rolling boil
15% of 100litres is 15 litres --- which is a nice rolling boil
15% of 200litres is 30litres --- which is a nice rolling boil

Its not an exact thing, 15% on your system is going to be different to 15% on mine... thats why there is a recommended range 8-15% that should give most homebrew systems (and many commercial ones) a nice rolling boil, safe in the knowledge that they are doing all the things that need to be done in a boil, but not boiling so hard that damage could be done.

As Andrew said, if you aren't willing to change your heat, or your lid arrangements, or even your kettle, then dont worry about it, you get what you get and have to live with it... And if you don't make large changes in the volumes you brew, then it just doesn't matter once you have established that your boil is at a reasonable level in the first place

I prefer to go to the extra trouble to alter my system, because I frequently alter my batch volumes. Otherwise I would just say 4 litres an hour too, which is what I get in my "standard batches"

If you are one of the people like Sammus who just cant get a boil at all without exceeding 15%.. then obviously you just have to... or you could try whacking on a lid or something, its pretty obvious that your system falls outside the parameters of the assumptions behind the theory.

I'm not trying to tell people that they should or shouldn't do anything at all... I was just trying to explain the purpose behind the use of a % figure when quoting recommended boil off rates. People seem to think that it is flawed... but its just a communication gap, they are using the % figure for the wrong purpose. Was just trying to fill that communication gap.

Thirsty


----------



## Sammus (21/8/07)

Thirsty, FWIW I see your point and totally agree. And when I say 'can't get a boil' its more like...can't get what I think of as a rolling boil. I'm almost certain that peoples idea of a 'rolling boil' differ greatly. Which is why I guess we should be talking in % evap in the first place 

Screwtop: I also use a CUB 'style' 50L vessel with the hole cut right to where the handles might be if it were at CUB keg.

I also use one of rambo burners that mashmaser sells. I like to hook it up to my BOC adjustable reg and watch it do its magic at 350kpa... not once its already up and boiling of course :unsure:


----------



## Thirsty Boy (21/8/07)

Sammus said:


> . . . can't get what I think of as a rolling boil. I'm almost certain that peoples idea of a 'rolling boil' differ greatly. Which is why I guess we should be talking in % evap in the first place  . . .



precisely


----------



## kook (21/8/07)

Should a rolling boil not be visibly, "rolling"?

Maybe it's just my system then, but if I adjust my burner down on a smaller batch in my kettle to ensure the same evaporation rate, I only "simmer" the wort. I don't get a rolling action occuring unless I increase the heat.

Maybe as homebrewers we misinterpret the meaning of rolling boil?


----------



## pint of lager (21/8/07)

Quite some time ago I found a definition of rolling boil for brewers to be about 25 mm difference between the peaks and troughs on on the surface of the wort.


----------



## kook (21/8/07)

pint of lager said:


> Quite some time ago I found a definition of rolling boil for brewers to be about 25 mm difference between the peaks and troughs on on the surface of the wort.



See thats what confuses me. If I was to boil that hard with say 10L in a 100L kettle, I'd probably get 50%+ evaporation in an hour. To reach 15% you'd need to simmer very gently.

Whilst this:

15% of 10litres is 1.5litres --- which is a nice rolling boil
15% of 100litres is 15 litres --- which is a nice rolling boil
15% of 200litres is 30litres --- which is a nice rolling boil

Sounds great in theory. It doesn't reflect what I've observed in practice. At least if a "nice rolling boil" is 25mm peaks and troughs on the surface.


----------



## big d (22/8/07)

These days i tend to follow my refractometer readings during the boil and adjust accordingly.At times a simmer as described by Kook and other times to achieve my target i crank up the heat to achieve the 25mm peaks and troughs as described by Pint of Lager.

Cheers
Big D


----------



## Thirsty Boy (22/8/07)

kook said:


> See thats what confuses me. If I was to boil that hard with say 10L in a 100L kettle, I'd probably get 50%+ evaporation in an hour. To reach 15% you'd need to simmer very gently.
> 
> Whilst this:
> 
> ...




But you have of course hit the nail on the head.. you probably couldn't boil that hard in a 100 litre kettle without getting a stupidly high evap rate.. this would be an indicator that if you want to brew 10litre batches, you are going to have to change something. (fairly drastically)

Remember I have been saying that changing the level of heat applied is just one of the things you can do.

If you were for instance to change to a different kettle size, more appropriate to the batch size, then you would find that you could get much closer to around 8- 15% per hour and be achieving the whole 25mm peak to trough delta.

Some sort of lid arrangement might do some of the trick, but probably not enough in the 10litres in a 100litre pot situation.

Or perhaps you could try a much smaller _sized_ burner, and off set it to the side of your very large kettle. The wort would boil vigarously in a localised area of the kettle, and a circulation style current would be set up exchanging the whole volume of wort through the area of "vigor"

Or if you really wanted to get out there.. you could use the smaller (size not nec power), more localised heat source and introduce your vigor via a mechanical stirrer. The wort doesn't care how the vigor gets there, as long as its there.

Lots of different possible solutions.. the point is that because you are well outside the 8-15% range.. you are being given a strong hint that all isn't well and something needs to change. So you can go looking for those solutions. If you were in that range and the wort is actually boilng... then you can be reasonably confident that things are hunky dorey and you can just make some beer.

BTW: great reference POL... seems just about spot on to me.

Thirsty


----------



## devo (5/9/07)

I recently managed to pull 20% evaporation on a 27lt batch after using a 50lt converted keg and my newly acquired Italian HP burner. I tell you what the boil was a tad more violent rather than a steady rolling boil so I think I may have to tweak it back a notch in future. <_<

I usually get around 11% when using my 100ltr ally pot.


----------



## Ducatiboy stu (5/9/07)

I have also noticed that the weather has an effect on evap rates.

Can be a PITA sometimes


----------



## apd (5/9/07)

braufrau said:


> This is bit OT but I was pondering the logistics of AG the other day and thinking what do the outdoors guy do if, say, an autumn leaf lands in the kettle! :unsure:



Same thing you do when an insect lands in there. Curse the little bugger and flick him out.

Although it helps if you can spot them going in there in the first place. I racked to secondary last night and discovered a little waspy thing stuck in the krausen ring. Best tasting beer out of primary I've ever brewed. Time will tell if the finished product stands up.

Andrew


----------



## apd (5/9/07)

Thirsty Boy said:


> 15% of 10 litres is 1.5lires/hour - a nice gentle rolling boil..
> 15% of 22 litrs is 3.4lires/hour - a nice gentle rolling boil..
> 15% of 45 litres is 6.75litres/hour - a nice gentle rolling boil..



The penny just dropped Thirsty. Thanks!

Andrew


----------



## blackbock (5/9/07)

All of this is very interesting but I wonder just how many of you do know exactly how much you are boiling off per hour? I still haven't worked out how to predict this accurately from batch to batch. I usually allow about 5L per hour, and sometimes this works out close to correct for me, other times I find that my batch has shrunk significantly and I scratch my head to work out why it varies so much.

A rolling boil with 25mm height sounds like a simple definition, but I'm sure as hell not about to try and measure the peaks and troughs of a 50L kettle of boiling wort. I figure as long as the wort is bubbling enough to move a hopsock around a fair bit it should be enough to do the job. It seems like a waste of energy to boil off nearly a quarter of a batch in an hour to me.

All of the advice I've ever heard suggests that keeping the lid off during the boil is the way to go, so that's what I do. 

If fraser_john does work out a system to accurately predict the Kettle Evaporation Rate I want to hear all about it.


----------



## devo (5/9/07)

blackbock said:


> All of this is very interesting but I wonder just how many of you do know exactly how much you are boiling off per hour? I still haven't worked out how to predict this accurately from batch to batch. I usually allow about 5L per hour, and sometimes this works out close to correct for me, other times I find that my batch has shrunk significantly and I scratch my head to work out why it varies so much.
> 
> A rolling boil with 25mm height sounds like a simple definition, but I'm sure as hell not about to try and measure the peaks and troughs of a 50L kettle of boiling wort. I figure as long as the wort is bubbling enough to move a hopsock around a fair bit it should be enough to do the job. It seems like a waste of energy to boil off nearly a quarter of a batch in an hour to me.
> 
> ...



I use BrewAlchemy which has an evaporation calculator.


----------



## blackbock (6/9/07)

Sounds worth a look Devo...


----------



## devo (6/9/07)

blackbock said:


> Sounds worth a look Devo...



It's a pretty good piece of software that runs on an OSX platform. Updates come out quite regular as well.


----------



## blackbock (6/9/07)

d'OH! Mac only...


----------



## fraser_john (6/9/07)

blackbock said:


> If fraser_john does work out a system to accurately predict the Kettle Evaporation Rate I want to hear all about it.



Sorry, but I have the same quandry you do! Some days it appears I boil off about 10%, other days it gets as high as almost 20%!!! I use Promash boil off calculator using before/after volumes.

It seems dependant on so many factors, SG, weather, breezes, initial volume etc.

I am at the point of resigning my self to setting my Promash default setting to around 12%. If I get a little extra chilled wort at a lower SG, oh well, its a weaker beer and it goes further. If I get a little less chilled wort at a higher SG..... I go to bed earlier when drinking it.


----------



## Julez (17/2/08)

fraser_john said:


> In the past I have "estimated" my kettle evaporation rate, and it has been a dismal failure. Tomorrow night I am planning on a true experiment by measuring in 40 litres of water and doing a full hours boil and chilling through the CFC to get my rate figured out once and for all.
> 
> Have others done this or do they do their best estimation as well? If so, complete the polls so we get an idea.
> 
> Personally, I use a converted keg, I had an extra 6 inches of height welded in so I can do a full vigorous boil of a 38 litre batch without fear of a boil over.



This may be an old topic, but a very interesting one!! After my first AG with a HUGE loss due to evaporation that didn't tally much with any indicative evap figures I had previously read, I had to go in search of some answers. This thread was full of them, but the below cut + paste from Wikipedia sums up causes of evaporation quite nicely: 

Factors influencing the rate of evaporation 
Concentration of the substance evaporating in the air: If the air already has a high concentration of the substance evaporating, then the given substance will evaporate more slowly. e.g. humidity in the tropics compared to dry areas
Concentration of other substances in the air: If the air is already saturated with other substances, it can have a lower capacity for the substance evaporating.
Flow rate of air: This is in part related to the concentration points above. If fresh air is moving over the substance all the time, then the concentration of the substance in the air is less likely to go up with time, thus encouraging faster evaporation. This is result of the boundary layer at the evaporation surface decreasing with flow velocity, decreasing the diffusion distance in the stagnant layer. e.g boiling outside
Concentration of other substances in the liquid(Impurities): If the liquid contains other substances, it will have a lower capacity for evaporation.
Temperature of the substance: If the substance is hotter, then evaporation will be faster.
Inter-molecular forces: The stronger the forces keeping the molecules together in the liquid state the more energy that must be input in order to evaporate them.
Surface Area: A substance which has a larger surface area will evaporate faster as there are more surface molecules which are able to escape. e.g. brewing a small batch in a large pot - this was my problem. Surely this is also the reason most people seem to report similar evap amounts in litres, almost irrespective of batch size (assuming the same kettle is used). A number of posts reported, say 4L of evap, whether it was a 20 or 40L boil. If the kettle used is the same size for both batches, the surface area is also the same and presumably, the QUANTITY of loss would also be similar (but not the rate)!
It's clearly possible to have a "nice, rolling boil", but a very large loss due to evaporation, if your kettle size is mismatched to your batch size. 

One question though - assuming you allow for a large loss due to evaporation, and match your hop additions and boil times accordingly, while also maintaining a gentle, rolling boil that everyone refers to, then is there a problem with say 40% loss in this scenario? This is what I had with a 15L batch in a 50L kettle. In my case, it caused me to stuff up the gravity and IBU calcs, but it was my first AG run and my losses were based on estimates only. If this loss rate is allowed for though, is it in itself a problem? I'd like to continue doing small batches in my largish kettle, rather than up the batch size unecessarily. 

Cheers, Julez.


----------



## domonsura (17/2/08)

Your evaporation rate is going to be fairly consistent( but with a small variance in it due to wind / atmospheric pressure / relative humidity), and is going to be more accurately given as a percentage of boiloff of your overall kettle volume, because the factors that affect it are boil vigour and surface are from which to evaporate from.

You will have the same surface area to evaporate from regardless of what volume you are actually boiling. The way you seem to be looking at it (apologies if I'm wrong and correct me if I am) you are expressing your evaporative loss as a percentage of the volume you are boiling which won't work.
In a 70 litre kettle, I used to get roughly 10 litres of evaporative loss over 60 minutes, which is just under 15% loss. As you are calculating it, if I was boiling 70 litres, I would lose that amount. However if I was boiling 35 litres, I still have the same surface area and same 10 litre loss, but 10 litres is nearly 30% loss of the boiled volume......(but still only 15% of the kettle volume.)
So when looking at evaporative loss, ignore the volume you are boiling (to a point) and calculate it solely on the volume of the kettle, as the _actual amount of loss_ will not fluctuate all that much in my experience.


----------



## Stuster (17/2/08)

Whatever you do, don't let Thirsty Boy see this thread.  

As domonsura says, you're going to get roughly the same evap volume in your kettle every time, whatever the volume. That is unless you reduce either the flame or the kettle opening. The first is not going to necessarily a good idea as you might not get the right level of hop isomerisation, protein coagulation etc etc. So, you can follow the 'Darren method'.  Keep the lid off for the first part of the boil, then partially cover the kettle. I do this to reduce the evap. rate for my kettle and it works for me.


----------



## Guest Lurker (17/2/08)

Hi Julez

Yes, for the purposes of working out your water requirements, you should use a rate of evap in l per hour, as using a percentage will get you in trouble each time you change the batch size.

You will get different answers on the effect of evaporating too much, mine is it wont cause any problems, and you should use the same pot and sparge a bit more and top up the kettle prior to or during the boil. Remember in designing an AG brew you are aiming to hit a gravity rather than a volume, although once you get used to it you will accurately predict both.


----------



## SpillsMostOfIt (17/2/08)

Guest Lurker said:


> ... Remember in designing an AG brew you are aiming to hit a gravity rather than a volume, although once you get used to it you will accurately predict both.



+1. Once you live this, life gets better, as does your beer.


----------



## mika (17/2/08)

I must be working backwards then. On principle I refuse to water a beer down, so I aim for the 20L I want into the fermentor and whatever the gravity is, is whatever the gravity is. But then I'm also not fussed if I end up with a litre or two extra.


----------



## Julez (17/2/08)

domonsura said:


> Your evaporation rate is going to be fairly consistent( but with a small variance in it due to wind / atmospheric pressure / relative humidity), and is going to be more accurately given as a percentage of boiloff of your overall kettle volume, because the factors that affect it are boil vigour and surface are from which to evaporate from.
> 
> You will have the same surface area to evaporate from regardless of what volume you are actually boiling. The way you seem to be looking at it (apologies if I'm wrong and correct me if I am) you are expressing your evaporative loss as a percentage of the volume you are boiling which won't work.
> In a 70 litre kettle, I used to get roughly 10 litres of evaporative loss over 60 minutes, which is just under 15% loss. As you are calculating it, if I was boiling 70 litres, I would lose that amount. However if I was boiling 35 litres, I still have the same surface area and same 10 litre loss, but 10 litres is nearly 30% loss of the boiled volume......(but still only 15% of the kettle volume.)
> So when looking at evaporative loss, ignore the volume you are boiling (to a point) and calculate it solely on the volume of the kettle, as the _actual amount of loss_ will not fluctuate all that much in my experience.



Agreed! Percentage loss varies in relation to wort volume, but not by very much in relation to the kettle volume. THAT makes sense


----------



## Julez (17/2/08)

Guest Lurker said:


> You will get different answers on the effect of evaporating too much, mine is it wont cause any problems, and you should use the same pot and sparge a bit more and top up the kettle prior to or during the boil. Remember in designing an AG brew you are aiming to hit a gravity rather than a volume, although once you get used to it you will accurately predict both.



Thanks Guest Lurker, that's pretty much what I thought. It's obviously the overall balance that is important. Though volume does impact on that balance (if you get it wrong). But yep, agree with your comments, gravity (and IBU in relation to that gravity) is what you are aiming for, rather than volume. Cheers :icon_cheers:


----------



## Maxt (18/2/08)

I now boil in a 50L keg shaped vessel, and lose about 6L in a 60min boil. My 80L kettle has such a massive surface area that I would lose over double that in a 60 min boil.


----------



## Maxt (18/2/08)

I now boil in a 50L keg shaped vessel, and lose about 6L in a 60min boil. My 80L kettle has such a massive surface area that I would lose over double that in a 60 min boil.


----------

