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Evaporation Rate

I brewed an AG kit this weekend and noticed I lost about 1.5 gallon during the boil process. I don’t know where I should compensate for this loss.

I mashed 12lb grains @ 1.5 quarts per pound and sparged with 5 gallons. In my boil kettle I stopped sparging when I approximately reached a volume of 6 gallons. It boiled aggressively for about 60 minutes with a flame out rest of 10. When I transferred to my fermenter, I was short about 1.5 gallons.

Do I increase my sparge volume? Also, what would happen if I had added water to my fermenter to cover that 1.5 gallon loss?


What was the SG of the wort in the fermentor? Could you get by with diluting the wort to a lower SG? You can also reduce the vigor of your boil to decrease the evaporation rate. Maintain a boil temperature, for your elevation above sea level, instead of creating volcanoes. A vigorous boil only creates a darker wort not a better wort.

Boil temperature will decrease about 1°F for every 500 feet above sea level.

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And less wort :grinning:

Boil some known quantity water on your system, keep it at a nice rolling boil,for an hour. When it’s done and cooled enough, measure what’s left and that’s your boil off rate. For the sake of argument let’s say it’s 1.5 gallon, then you need to start with 6.5 gallons PRE-boil to have 5 gallons POST boil. 6.5 gallons is your pre-boil volume.

Now go mash with what you need. The grain will absorb some of the mash water, but that’s OK. After you drain the mash tun, see how much wort you have in the kettle. If you need 6.5 pre-boil, and say you get 4-gallons from the mash, then just take the difference; that’s 2.5 gallons. Sparge with that 2.5 gallons. Since the grain has already absorbed the mash water, it won’t absorb more, and you’ll get that 2.5 gallons out, and hit your pre-boil volume.

So nail your preboil volume, then keep a consistent boil, and you will hit your batch size.

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The one addition to jmck’s excellent advice is that some days, you’ll boil off more than others. Every January, I’m amazed that my boiloff rate pretty much doubles.

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I would also account for some trub left in the boil kettle too… starter at 6.5 for a standard brew… push it up to 7-7.5 for a big hoppy brew… Sneezles61

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As a newb, one of the things that struck me was the losses. It’s pretty intuitive that you’ll lose from boil off but things like trub loss, hydrometer sampling, “oops”, and the like even though not huge, all add up. I was very disappointed a couple of times with how short I came up at bottling. In planning my brews now, I think about samples, how many hops are going in, what kind are they, am I dry hopping, am I going to secondary? I vary my wort into the fermenter calculation based on those factors. In the end it always seems to be beer but it’s nice when the whole plan comes together. :slight_smile: Sounds like you’re on track to nail down those little nuances! Cheers!

If you’re using a counter flow chiller with a pump and hoses, there will be losses there as well. I start with 13 gallons pre-boil to produce 11 gallons of wort. Then I lose about another half gallon to trub, and plumbing.

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When do you start your timer on the boil? Do you wait until it’s boiling or right after the transfer to the boil kettle? I started my 60 minutes when I brought the wort to a boil, so this may also be part of my volume loss.


I know your question was directed to @jmck, but I start my timer once the hot break subsides.


For a brew, I start the timer when I drop the first hop addition, which is usually just about the time the hot break subsidies.
For the boil-off rate, start the timer when it boils.

I have taken to starting with 1/4-1/2ish gal more than I need in my kettle (I’ve been upping my mash and sparge volumes slightly to achieve this), then boil down to starting volume. Once I hit starting volume, I toss in the bittering charge and start the timer.


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