Kettle Evaporation Rate

[fraser_john]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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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

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]

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]

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]

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]

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]

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

 

[Steve]

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]

: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]

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]

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]

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: