Author Topic: Evaporation Rate  (Read 1218 times)

Offline flbrewer

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Evaporation Rate
« on: March 24, 2015, 08:01:32 PM »
Is there a standard boil evaporation rate that people try to stay close to? I ask this because I always just assumed it was 1 gallon/ hour. With my burner I can control pretty tightly how vigorous my boil is and noticed on my last boil that I only boiled off about 1/2- 3/4 gallon.

Perhaps a better question instead of boil off rate would be what type of boil is preferred?

Offline goschman

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Re: Evaporation Rate
« Reply #1 on: March 24, 2015, 08:07:19 PM »
I think the goal would be to have reproducible post boil volumes. I mark my regulator with a sharpie so that it is the same from batch to batch. Temp swings throw it off but that's too hard for me to adjust for...

FWIW, my preboil volume is 6.23 gallons with 5.35 gallons going into the fermenter on average. I lose about 1 qt to yeast and trub so end up with just over for 5 gallons of finished beer which is perfect for me.

Like you, I assumed that 1 gallon per hour is about normal...I see a lot of recipes for 6.5 gallons pre boil and 5.5 post
« Last Edit: March 24, 2015, 08:13:37 PM by goschman »
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Offline Stevie

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Re: Evaporation Rate
« Reply #2 on: March 24, 2015, 08:48:04 PM »
With my current kettle and environment, I loose about 1.5 gallons per hour. That is high, but what can I do? I set my boil as low as possible. Indoors for small batches I am at about 1 gallon.

Offline HoosierBrew

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Re: Evaporation Rate
« Reply #3 on: March 24, 2015, 10:01:07 PM »
I normally stay at ~ 1.2 gallons/hour.
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Offline duboman

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Re: Evaporation Rate
« Reply #4 on: March 25, 2015, 12:05:54 AM »
I've a got a shorter, wider kettle and boil off 1.75 gallons with a good rolling boil, I know its a lot but I'm not ready to invest in a new kettle with better dimensions.
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Offline a10t2

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Re: Evaporation Rate
« Reply #5 on: March 25, 2015, 01:32:48 AM »
10%/hour, with a 75 min minimum boil, is what I shoot for. Granted, this is at 10 psi, so all kinds of things are wacky. At lower elevation I'd imagine you could boil off less given the higher temperature.
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Re: Evaporation Rate
« Reply #6 on: March 25, 2015, 01:34:03 PM »
Most home brewers boil too rapidly.  I do not know where the "rolling boiling" thing originated in home brewing.  However, the boil only needs to strong enough to disturb the surface, which another forum member described as a "hard simmer."  Losing more than 15% per hour to evaporation has a negative effect on beer stability and quality.  I did not realize the difference a lower evaporation rate made until I started to use an induction range that was incapable of producing a hard boil.  The maximum amount of evaporation that should occur with 6.5 gallons in an hour is 0.975 gallons.  Ideally, the evaporation rate should be 0.65 gallons per hour.
« Last Edit: March 25, 2015, 02:16:30 PM by S. cerevisiae »

Offline Wort-H.O.G.

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Re: Evaporation Rate
« Reply #7 on: March 25, 2015, 01:48:55 PM »
I have a tall kettle, and average about 1.1-1.2 gals per hour. i boil 75 minutes for most - pils malt or most my lagers boiling 90 minutes.
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Offline mabrungard

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Re: Evaporation Rate
« Reply #8 on: March 25, 2015, 07:52:17 PM »
I agree with Mark that the boil needs to be active enough to roil the surface a bit and you can actually see trub being moved through the kettle by the boil action. You don't need to have a volcano in the kettle.

When I first started using my electric kettle, I was surprised to find that I could boil off about 2 gal/hr. That was way too much. I finally learned how low I needed to turn down my element to bring the boil down to a more normal rate of about 1 gal/hr.

From what I can tell, excessive boil-off rate doesn't do anything good for the brewer. In essence, you will have to make up for that lost water either through a larger pre-boil volume or with a make-up water addition at the end of the boil. Neither is energy efficient. The other consideration is that the wort never gets any hotter and the isomerization rate is not increased, nor is the rate of DMS production or volatilization.

Therefore, it appears beneficial to reduce your heat source and aim for a more typical evaporation rate around 1 gal/hr.
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Offline pete b

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Re: Evaporation Rate
« Reply #9 on: March 25, 2015, 08:19:03 PM »
My electric stove turned on high with my 5 gal kettle does almost exactly 1 gal/hr. When I use my propane burner outside with my wider 15 gal pot I can't go below 1.25 gallon/hour with consistent results.
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Offline flbrewer

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Re: Evaporation Rate
« Reply #10 on: March 26, 2015, 12:23:16 AM »
OK, so I did some "scientific" testing this evening. Poured 2 gallons in my brew kettle and boiled for 15 minutes. I ended up with 7 quarts of water after the boil. This is 4 quarts (1 gallon) an hour which surprised me as I tried to keep the boil down a bit.

Based on S. cerevisiae's comments, I should be aiming a little less than that. I certainly don't want to add anymore steps in my brew day at this point, but I'm wondering if I shouldn't just check the temp. of the boil vs. looking at the actual boil to gauge where I am. My point being that if I'm at 212 then it's boiling technically.


Offline Stevie

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Re: Evaporation Rate
« Reply #11 on: March 26, 2015, 12:31:16 AM »
Like efficiency, I think this is a spot where it is easy to get stuck chasing the dragon. Do what works for you and makes you good beer. I am confident that I have as little boil off as possible in my current environment with my current kettle and burner. I'm happy, beer is good, I'm moving on.

Percentages of boil off are absolutely useless here, IMO. Geometry, temperature, wind, and humidity all play a role. Plus when I brew 5 gallons, the boil off is the same as when I brew 10 gallons.

Offline HoosierBrew

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Re: Evaporation Rate
« Reply #12 on: March 26, 2015, 12:37:17 AM »
Like efficiency, I think this is a spot where it is easy to get stuck chasing the dragon. Do what works for you and makes you good beer. I am confident that I have as little boil off as possible in my current environment with my current kettle and burner. I'm happy, beer is good, I'm moving on.

Percentages of boil off are absolutely useless here, IMO. Geometry, temperature, wind, and humidity all play a role. Plus when I brew 5 gallons, the boil off is the same as when I brew 10 gallons.

^^ All of this.  I'm pretty sure I make good beer boiling off 1.2 gal/hr. If you were 1.8+/hr, it might be time to dial the burner back.
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Re: Evaporation Rate
« Reply #13 on: March 26, 2015, 12:48:23 AM »
Like efficiency, I think this is a spot where it is easy to get stuck chasing the dragon. Do what works for you and makes you good beer. I am confident that I have as little boil off as possible in my current environment with my current kettle and burner. I'm happy, beer is good, I'm moving on.

Percentages of boil off are absolutely useless here, IMO. Geometry, temperature, wind, and humidity all play a role. Plus when I brew 5 gallons, the boil off is the same as when I brew 10 gallons.

^^ All of this.  I'm pretty sure I make good beer boiling off 1.2 gal/hr. If you were 1.8+/hr, it might be time to dial the burner back.

+i've not seen any conclusive data that 1 gal per hr boil is better than 1.5 gal/hr boil beer.
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Offline flbrewer

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Re: Evaporation Rate
« Reply #14 on: March 26, 2015, 12:49:02 AM »
(Backs out of rabbit hole slowly)