Question about boil volume using extract kit

Hi All,

I’m a newbie here and fairly new to home brewing … about 3 years now.

The Northern Brewing kits all give instructions to boil 2.5 gallons of water. I assume that is because many extract brewers have only common kitchen pots for boiling. I have purchased a 10 gallon boil pot and a wort cooler. Since I have a 10 gallon boil pot, I throw in about 5 gallons of water at the start. Steep the grains in the 5 gallons of water and then continue to follow the instructions in the kit. At the end of the boil, the volume is usually a bit lower than 5 gallons due to evaporation loss, so I top up to 5 gallons.

My question … should I be adjusting the amount of hops because I am using 5 gallons of water instead of 2.5 gallons of water? I have heard that the attenuation of the hops is different when the specific gravity is lower as would be case with 5 gallons of water vs 2.5 gallons.


Isomerization of hop oils is said to increase in a wort of lower specific gravity than the same amount of hops in a higher gravity wort. I have read from 5% to 10% greater isomerization in the lower gravity wort. I don’t have any experience with this. I’m unable to do full 5 gallon boils.

A recipe calculator, like the free one here, may give you an idea of how the IBUs may increase with a full boil compared to a partial boil with your recipe.

Flars answer is right on. If you boil in 5 gallons instead of 2.5 or 3 (typical for extract brewers), you should decrease the amount of bittering hops (60 minute addition) by 10%.

The big benefit to using a full boil is that your beer won’t darken as much; it’s pretty much impossible to brew a truly light colored beer using concentrated boils.

I’m curious about your experience adding your crushed grains to the full kettle. That is one of the things that people warn against; it is suppose to cause tannin extraction from the grains due to the highly dilute nature of the soak. Have you noticed anything consistent with that, or is it just one more myth about brewing?

If you’re doing a NB extract kit that has a corresponding all-grain kit, compare the hop schedules, which is easy since NB posts the recipies. So for example, my go-to, Dead Ringer: In the extract kit the 60 minute addition is 1oz Centennial. In the All-grain kit it’s 0.75 oz. But you’ll also notice the 20 min, 5 min, and Dry Hops are identical.

I seem to recall reading in more than one source that you want to use 25% less in full wort boils which would go along with what jmck is seeing in the instructions for the Dead Ringer. Not sure how accurate this is, but I went to Brewer’s Friend IBU calculator and added 1oz of 10% AA hops (pellet) to a 6.5 gallon pre-boil, 5.5 gallon post-boil batch for 60 minutes and got 35 IBU’s. Then I changed the pre and post boil volumes to 2.5 and 5 keeping the OG the same (1.055) The IBU’s dropped to 22. The calculator assumes a pre-boil SG of 1.110. So it factors in the reduced utilization due to the higher wort gravity. The correct answer might very well be to use such a calculator for each individual batch and see what the difference is going to be.

Before I started almost a year ago,
I purchased Charlie Papazian’s book “The Joy of HomeBrewing”. On page 258 he has a very detailed chart on the approximate hop utilization percentage based on extract concentration and boil times. I have just the opposite problem as Steve, who led off this thread. I do not have a large enough kettle to accommodate 2.5 gals and added grain and ME. I have settled on dividing the batches in half and adding the ingredients in half parts as well. Based on Charlie’s table, I do not believe this should alter the boil time or Hop utilization during the boil. Anyone else have an opinion on this?


Boil time will not change. Dividing the ingredients by half should keep the recipe in proportion.

Some Information in a book can be out of date, based on newer brewing methods and research, by the time a book is written, published, and then purchased. I like to use online sources for recipes, hoping there are updates as new information comes out. Compare the chart in “Joy of Homebrewing” with hop utilization estimations in Brewers Friend recipe calculator.

Brewtoad also has a free recipe builder.

I’m really saying that I don’t use one source as gospel.

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Sorry if it’s a dumb question, but I’m a little confused by what you describe above…are you simply using half the kit ingredients to make a 2.5G batch? You should not have to adjust anything as long as you’re not changing the concentration of ingredients in the boil.