Converting from 5gal to 3gal partial extract

I'm planning on doing the Lagunitas IPA clone from BYO. In the article there is this quote:


I plan to do a partial boil. I'm a little confused about how to convert the recipe to a 3 gallon boil. From this forum I've gathered most of the brewing programs use old (incorrect) calculations for hop utilization. (I.e. they assume a late addition of LME will result in higher IBUs). How does the volume of the boil affect hop utilization? If the programs are wrong with the calculation, what is the best way to convert the recipe?

The problem for high-IBU beers isn't the utilization, it's the dilution. You can only dissolve the bittering compounds to a certain concentration, which is in the neighborhood of 100 IBU. Adding hops past that point won't make it any more bitter.

If you have 3 gallons at 100 IBU, then dilute it to 5 gallons, you've only got a 60 IBU beer in the end. For a partial mash, the highest achievable bitterness will be roughly 100 * (final boil volume)/(total volume).

If you want a higher bitterness than that, there are two things you can do: 1) increase your boil size, 2) decrease your batch size. There's nothing wrong with making a 3 gallon batch!

This is only a 60 IBU beer. I'm not opposed to a 3 gal batch (but would prefer a 5). Either way I'll need to convert the recipe.

Edit: sorry missed the calc on my first read. (stupid smart phone).

The easiest way to do conversions is to find beer software (you can buy it, or there are some decent free ones---I use BrewTarget, which runs on essentially any OS).

If you can manage even a slightly bigger boil (and note that I'm talking about post-boil volume, so after you've accounted for boil-off), that will help considerably. A 60 IBU is going to be tough, because I don't think you're guaranteed to even get to 100 IBU just by throwing in the hops that you calculate. I think other factors may come into play because you're really trying to saturate the wort. This is a bit out of my league, though.

Another possibility would be to brew two separate batches and combine them. It means twice the brewing time, though.

I guess my question is how valid are the brewing software programs? If they take into account a bad assumption (regarding LME late addition)?

Plugging my recipe into Hopville with full boil gives 51.8 IBUs. With 2.25gal top off it goes down to 36.4 IBUs. If I multiply the hop schedule by 1.5 with the topoff I get 54.7 IBU's. Does this seem right?

Also - not sure I agree about not being able to brew a hoppy beer using partial boil. That may be the case with a super hop bomb (100 IBUs), but I've done several batches of IPAs that have turned out very good - and as hoppy as expected.

Regarding the software accuracy, I really don't know. I have generally taken them at their word, ignoring the question of whether the boil gravity component of the equation is correct. I'm not interested in big-IBU beers, and there are enough uncertainties in the procedures that I'm really only aiming for a ballpark.

What boil volume are you using for the full boil / the 2.25 gal top off? That doesn't sound quite right to go from 51.8 to 36.4 by dilution (assuming you had 2.75 gal boiled, you'd expect 51.8*2.75/5 = 28.5 IBU).

54.7/36.4 is roughly 1.5, so that part of the calculation doesn't seem to be doing any magic to include nonlinear effects, and is just what you'd expect from dilution. The pre-dilution bitterness is right at 100 IBU, so I suspect you're at or past the range where the software's assumptions are valid.

As I said, I don't have any experience trying to do high-IBU beers, but I don't doubt you can get a very hoppy beer even with a partial boil. That doesn't necessarily mean it's super-high IBU, though, as most of us can't taste the number of IBUs. Plus, the character of the beer will have a big impact on how a given number of IBUs will be perceived.

Anyway, I've said way more here than I have the experience to back up. Best of luck on your brewing.

Fair enough - thanks for your input. I've run calculations through Beersmith, Hopville and Brewtarget - with similar results. I think there may be a typo with the recipe as the IBUs do not match up to what is stated on the recipe (assuming full boil). I also tried plugging in the AG recipe into Beersmith - and the IBUs were on the low side.

Since I also have the AG recipe, I did try the Beersmith conversion tool from AG - the hop schedule was about 1.5x the recipe. I'd like to try it - but its not exactly an inexpensive mistake if it doesn't work out.