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?
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
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.
I normally stay at ~ 1.2 gallons/hour.
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.
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.
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.
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.
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.
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.
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.
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.
(Backs out of rabbit hole slowly)
Not so sure on this one, guys. At what boil rate are you ridding Pils malt of its SMM? I tend to push the pilsners pretty hard for at least a goodly portion of a 90 minute boil. No science behind this, just what I had always heard and the results have been favorable. I guess it’s time to call the Brulosopher…
Commercial brewers have a pretty vigorous boils from the ones I have seen. The 100 bbl system at Sierra Nevada Chico looked like the volcano. The boil off rate is down around 5% as they have a small stack for the vapors to escape.
I wish we could get rid of the concept of percentage boil-off. It makes no sense. Consider 5 gallons of wort boiling at 1 gal/hr:
Hour vol %/hr
1 4 20
2 3 25
3 2 33
4 1 50
5 0 100
A fixed rate of fuel supplied boils off a fixed amount, not a percentage.
I agree with you, Rob. If the wort surface area in the kettle is constant with respect to depth, then the boil off rate is likely to be constant too. My observations are that it is a constant rate in my system.
The problem with that strategy is that water is vaporized into steam 100C at standard atmospheric pressure; hence, the temperature does not rise as the boil rate is increased. The extra heat energy is carried away with the vapor (see Latent Heat of Vaporization). This physical phenomenon is the reason why we have to heat water under pressure in order to increase that temperature at which it converts into steam. The weight that is used on a pressure cooker/canner raises the internal pressure of the cooker 15 lbs above atmospheric pressure. If the external pressure is standard atmospheric pressure, water will not boil until the internal temperature reaches 121C (251F).