Question on hop utilization and IBU's

Hi all.

I'm brewing my first batch this weekend. I've got my recipe formulated for a 2.5 gallon batch that was to have 1/2 oz of Chinook pellets in the boil for 60 minutes, and 1 oz of Cascade pellets for 15 minutes. Then I was going to dry hop in the secondary with whole leaf Cascades.

So I was doing a dry-run last night, and I realized that I failed to take into account the capacity of my brew kettle, which is a stock pot. I'm only going to be able to boil 3/4 of a gallon of the wort, whereas my recipe is formulated for boiling 2.5 gallons and topping off only what evaporated during the boil. (I don't know what I was thinking).

So I used the "recipator" to adjust the level of hops, and it appears that I will need quite a bit more bittering hops (almost 4 times more!) given the smaller boil. I'm assuming that the high gravity of the concentrated wort is responsible for the reduced utilization potential of the hops?

Anyway, my question is what is the difference between the Tinseth and Rager utilization method? I came up with a formula that would yield 30 IBU’s using Tinseth, then I clicked Rager and it came up as 81! That’s a big difference.

Sierra Nevada lists their famous Pale Ale as having 37 bitterness units. Any idea which utilization method they use? I’m confused because IBU’s are often listed for commercial brews, but I don’t remember there being more than one system. I want to be sure that I end up with 30 of the IBU's I'm famiar with, not 81.

Any light that can be shed on this is appreciated.

I don't believe that your boiling the hops in less wort than the full volume will matter much in the overall IBUs imparted to the recipe.

The bitterness will be released in a concentrated amount into your small boil and then will be watered down into the full batch size. Same idea as the gravity.

cowain said:

I don't believe that your boiling the hops in less wort than the full volume will matter much in the overall IBUs imparted to the recipe.

Click to expand...

Actually, hop utilization is dramatically affected the the SG of the wort...utilization goes way down as the SG goes up, so that you do in fact need to use more hops in a partial boil.

Samuelzero, here's an article from BYO that I think answers your question.

3/4 of a gallon seems really small. i have a pot i use just for priming that is 3 gallons!

anyway the general theory is that the higher the gravity, the lower the hop utilization. i use Dave miller's sytem where by a 3 gallon boil will get you 20 percent utilization, that is 1 ouce of 10 a.a.u. x 20 / 6.7 = 29 i.b.u.'s so if you half that twice (3/2=1.5/2=.75) = 29/2=14.5/2=7.1

somehow i dont think 7.1 i.b.u.s is accurate, i would recomend boiling at least 1.5 g to get you a decent utilization.

Papazain rates his utilization alot higher, he gives 30 percent for a full 5 gallon boil, 25 percent for 3 gallons.

Yeah, as you make the boil more concentrated, you'll seriously affect hop utilization. Personally I'd recommend running down to walmart or somewhere similar and picking up a larger pot.

samuelzero said:

Anyway, my question is what is the difference between the Tinseth and Rager utilization method? I came up with a formula that would yield 30 IBU’s using Tinseth, then I clicked Rager and it came up as 81! That’s a big difference.

Click to expand...

Turns out this is as big a controversy as glass vs plastic, but only among the truly geeky. The consensus seems to be that for partial boils, the Rager method is more accurate, while for full boils the Tinseth method is closer. Here's some light bathroom reading that goes into all of the whats and wherefores.

Estimating Hop Bitterness
Glenn's Hop Utilization Numbers
Deja IBU

samuelzero said:

Sierra Nevada lists their famous Pale Ale as having 37 bitterness units. Any idea which utilization method they use? I’m confused because IBU’s are often listed for commercial brews, but I don’t remember there being more than one system. I want to be sure that I end up with 30 of the IBU's I'm famiar with, not 81.

Click to expand...

Large scale breweries don't have to calculate the hopping rate the same whay we do. They are able to do test batches and account for the many other factors specific to the brewhouse design that affect the hop utilization. The actual IBUs of the test batches (and the final product) are measured in a lab.

Since the equipment of measuring IBU's is rather expensive, we home brewers have to rely on utilization tables (Tinseh and Rager being the most common ones) to estimate the final IBUs of the beer. Your problem is the very high gravity of the boil which exposed the difference between these 2 tables.

Kai