# Evaporation Rates



## Spiesy (18/5/12)

Hey there AHB crew,

I know people are quite sensitive to new topics, so I've attempted to use the search function, but after scrolling through the first 4-pages of results, and consulting the 'AHB Resources', I have resigned to making this topic (although I'm sure someone will soon drop a link in to a thread I've overlooked).

So, what evaporation rates are you receiving during your boil? 
Do you calculate percentage lost, or volume lost per hour? 
What size is your kettle, and what sort of heat are you applying (fierce boil, gentle boil)? 
Lastly, and to a lesser extent - what is your average ambient humidity like?


I'm trying to formulate my rate. I was told to go with 10%/volume p/hr. But I read on another forum (whilst searching), that it shouldn't have anything to do with your volume (as long as you don't boil dry!), as it's more to do with the surface area, heat applied and ambient humidity... which makes sense to me.

I'm using a 70l stainless pot (from Craftbrewer), fairly gentle-mild boil, mildly dry humidity (Melbourne) and have NFI what my evap rate is (I'm a noob, and would appreciate a starting point... brewing tomorrow). 

Cheers lads/ladettes.


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## QldKev (18/5/12)

Stick to the basics and you wont have issues. I like a nice strong rolling boil, not a simmer, but no need for it to be jumping out of the pot like a scene from Aliens. Don't worry too much about the pot dimensions, obviously a wider pot will boil off more. Don't be too worried about the altitude, relative humidity, day of the week, your hair color.

Measure your boil off in how much you boil off. eg pre boil = 26L, after boil = 23L. So you boiled off 3L with a start boil of 26L. Then we can calc a percentage just for a reference check 3 /26 = 11.5%. As long as your end in boiling off anywhere between 8% and 15% or your starting boil volume is great. So you care about the start volume, cause thats how much you need in the pot. The final volume, cause thats how much wort left over. And just check the %boil off to ensure it's in range. 


QldKev


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## Liam_snorkel (18/5/12)

Spiesy said:


> I'm using a 70l stainless pot (from Craftbrewer), fairly gentle-mild boil, mildly dry humidity (Melbourne) and have NFI what my evap rate is (I'm a noob, and would appreciate a starting point... brewing tomorrow).
> 
> Cheers lads/ladettes.


do a test run with water if you have a chance.
get one of those 500mm stainless rulers from the big green shed, measure the diameter of your pot, and use the ruler to measure the change in depth. work out your volumes from there.

for what it's worth I got 3.5 l/h with my crown urn. with I guess what you would call an 'average' boil.


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## Barry (18/5/12)

I use immersion heaters and reduce 30 L to 25 L in 90 minutes. This is nearly 17% or a bit over 11% per hour. It is a slow+ rolling boil. Hope this helps.


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## Parks (18/5/12)

I have the same pot and get approx 5.5L per hour. The pot is 45cm diameter and 45cm high (internally) making it spot on 70L to the brim.

I am yet to nail down 100% my evap rate as I seem to change how I boil and with the NASA you can go from subtle to ridiculous.


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## glenwal (18/5/12)

Spiesy said:


> so I've attempted to use the search function


Make sure you use the google search option in the top right, not the default search. The default search is rubbish.



Spiesy said:


> (although I'm sure someone will soon drop a link in to a thread I've overlooked).


Very first result from searching for your exact topic name :icon_cheers: 



Spiesy said:


> So, what evaporation rates are you receiving during your boil?


I generally boil off about 20-30% over my 90 min boil, so about 15-20% an hour. I do boil it quite hard though as I do maxi-biab on a stove top so i want to boil off as much as possible as I top up with sparge water to improve my effeciency.



Spiesy said:


> Do you calculate percentage lost, or volume lost per hour?


A % per hour figure will be the most useful to you as it can then be applied to any size batch for any boil length eaisly.



Spiesy said:


> What size is your kettle, and what sort of heat are you applying (fierce boil, gentle boil)?


A 20L Big W pot on the stove top. I've got a really good gas cooktop with a wok burner that gets are really fierce boil going. I think for normal brewing though, you want something in the middle - Just a good rolling boil.



Spiesy said:


> Lastly, and to a lesser extent - what is your average ambient humidity like?


I'm in sydney if that helps


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## Parks (18/5/12)

Glen W said:


> A % per hour figure will be the most useful to you as it can then be applied to any size batch for any boil length eaisly.


Except this doesn't hold true for different batch sizes. L/hr holds true for me, whether I'm boiling 20L or 65L (of course you have to ensure your boil look the same, you'll need less power to keep the same rolling boil on 20 vs 65)


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## MHB (18/5/12)

Boiling causes lots of changes to the wort; creating soluble bittering substances, condensing protein, denaturing enzymes... the evaporation part of the boil concentrates the wort and most importantly helps remove undesirable volatile compounds like the precursor to DMS and some unpleasant hop aromas.
These volatiles are carried off with the steam, thats why its important to let the steam escape and not have it condensing and running back into the kettle, returning the volatiles to the wort. If during the boil around 10% of the volume is boiled away you will have input enough energy to achieve all of the goals of wort boiling. 
Mark


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## Spiesy (18/5/12)

thanks for replies, some good advice here.

I will use the Google search from here on in.



MHB said:


> Boiling causes lots of changes to the wort; creating soluble bittering substances, condensing protein, denaturing enzymes... the evaporation part of the boil concentrates the wort and most importantly helps remove undesirable volatile compounds like the precursor to DMS and some unpleasant hop aromas.
> These volatiles are carried off with the steam, that's why it's important to let the steam escape and not have it condensing and running back into the kettle, returning the volatiles to the wort. If during the boil around 10% of the volume is boiled away you will have input enough energy to achieve all of the goals of wort boiling.
> Mark



very interesting.


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## hotchilli (16/8/12)

Are there any pros/cons with topping up the kettle with boiling water to replace that which has evaporated off?


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## Dave70 (16/8/12)

hotchilli said:


> Are there any pros/cons with topping up the kettle with boiling water to replace that which has evaporated off?




Most brewing software lets you set up for those losses anyway.
I've done this post boil however to get the OG where it needs to be if I've gone to long on the boil. 
Probably cos I was on the ride on mower and lost track of time. And drinking. 
Isn't that the idea of 'lawnmower' beer?


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