Originally Posted by Erockg13
Hi I'm a home brewing beginner and I have a question. I've been looking at recipes and some are wanting the pre boil volume to be 4 1/2 gallons and some call for 2, 3, etc. now I have a brew kettle that is 20 QTs so doing anything over 3 gallons is asking for trouble. I was wondering what the harm if any would be if I were to just do the same recipe with the modified boil volume adding water to a 2 gallon recipe to make it 3 and also subtracting from a recipe that calls for a 4 1/2 boil volume to 3 gallons. I'm brewing 5 gallon batches.
Yes, you can do that. There are some issues with reducing the boil size, but nothing insurmountable.
The first is simply that a concentrated boil produces more maillard reactions. Those are reactions, like the browning of bread and making toast, that are similar to caramelization. An easy way around that is to add the majority of the extract at flame out, at the end of the boil as it's boiling that causes those darkening reactions. That way, the beer has less of a "cooked extract" taste and more of a traditional beer flavor.
The other impact is hops utilization. Not so much the actual utilization, as the hops oils will isomerize for bitterness anyway, but if you're making a beer designed for a 5 gallon boil and boiling only 1/2 of it and topping up with water, in a few cases where the bitterness and hopping are high, you will be diluting the bittering units. That isn't a problem in many beers, but in beers where the bitterness is imperative, like in an IPA or Imperial IPA, or a barleywine, then that can be an issue.
Otherwise, you should be just fine with boiling as much as you can, and adding the majority of the extract at the end of the boil instead of at the beginning.
I'd suggest using a pound of extract, more or less as it's not exact, for every gallon of water in the boil. That will also give you more room in the pot for your 1 hour boil.