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Determing pre-boil volume

Hi all,

Well my first batch is fermenting away and I’m already thinking about my next batch.

Due to space limitations I would like this next batch to be 2.5 to 3 gallons. I know that some volume will be lost during the boiling process, so I need to start off with more than 2.5 to 3 gallons.
My question is: how do you determine the pre-boil volume so that you are at or near your planned final volume after the boil?
Is there a rule of thumb or formula that is used, or do I need to use some kind of brewing software?


Yes, you should be using brew software. I personally use and like BeerShith. How much ever you boiled off in your first batch will be pretty much the same for any size batch. If you don’t know what that was, measure three gallons of water into your kettel and boil like you would if brewing for the same length of time and measure what you have left, difference is your boil off.

Brewing software is by no means required to brew beer. I have been brewing for almost three years and never really used any software. The only calculations that I used software for were calculating IBUs ( and pitching rates (

To answer your question about boil off, most people find that 1 gallon per an hour is pretty standard starting point. So if you want 3 gallons of wort post boil, start your boil with 4 gallons. If you find that you boil off is more or less then 1 gallon per an hour you can adjust it on future brews. Essentially just trial and error, but 1 gallon per hour is a good starting point.

In reality there are several factors that will affect your boil off rate. Temp, Humidity, Kettle Size, Boil strength, altitude. Over time you will figure out your system and its boil off rate.

This is easy.

First add the volume you think you might lose in the bottom of the primary fermenter. I usually figure a pint per batch, or for a highly attenuative yeast or a beer with a ton of hops, I’ll add a whole quart. So thats:

+0.125 or +0.25 gallons (it’s a little bit of a swag)

Then add the amount of water that will be boiled off. It’s normally 1 gallon per hour of the boil for a good vigorous rolling boil, which is what you want for the best beer. If you’re only boiling for 15 minutes, it’s a quart lost. If you boil 90 minutes, it’s 1.5 gallons. Pretty easy. So:

+1 gallon for all-grain (probably) or +0.25 gallon for extract (probably)

Done. So, for a 5 gallon batch of all-grain beer, I would suggest starting with about 6.2 gallons pre-boil and see where that gets you. If making 3 gallons of extract beer, you may need to start with 3.5 gallons if doing a 15 minute boil, or as much as 4.25 gallons if boiling for a full hour.

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