Accurate Alpha Acids

[TycoRossBrewing]

So I have some questions about calculating the HBU of my beer.

People say adding one oz of a 10% alpha acid hop to a brew will add 10 HBU points to the final product for five gallon batches. First off, is this correct. Does this point system work for 5 gallon only and i would have to do the math if adding hop to a larger batch?

Also, and more importantly, does this scale only work for a certain boil length? I would assume that adding a 10% alpha acid at five or ten minutes til flame off will impart a different level of alpha acids than adding the same hops at 60 or 90 minutes. Is there a way to calculate HBU bases off of the original equation? Does dry hopping increase the AA`s as much as boiling the hops?

 

[joshesmusica]

can't speak to the amount of bittering units it adds specifically. i simply use beersmith for my calculations. much less of a headache. but if you're just trying to figure out the actual math/science behind it, i give you made props.

different boil lengths add different amounts, as isomerization occurs. the lower the temp, the less isomerization occurs, and it stops at around 175F. so if you're doing a hopstand, and you cool to 170F first, it will stop the isomerization, but still extract the oils. same with dry hopping. too low of a temperature to add any AAs, but hopefully still high enough to extract the right oils for flavor and aroma. As far as hop utilization in the boil, there are many factors that go into it, but here is a good place to get you started:
http://www.howtobrew.com/section1/chapter5-5.html

 

[FirstAidBrewing]

Mostly you are follow the AAU/HBU guidelines so that your brew matches the recipe you are following. Yuu can then extrapolate to make a bigger batch, but the main idea is to ensure that you are using the correct AAU in the event that one year, your hops are 10% and the next they are 12.

I would personally use IBU calculations (or BeerSmtih) to figure out the bitnerness as opposed to HBU's.

 

[ajdelange]

A rating of 10% alpha means that 10% of the weight of the hops is bittering principal. IOW if you add 30 grams of this hop to a brew you will have the potential for 0.1*30 = 3 grams or 3000 milligrams of potential bittering to the beer. If the brew is 20 liters that is approximately 3000/20 = 150 mg/L. If the brew is 40 liters it is 3000/40 = 75 mg/L etc.

Not all the potential is realized. The amount depends on the length of the boil, the strength of the wort, the vigor of the boil and the geometry of the kettle. Suppose you get 35% utilization. For the 20 liter brew you would realize 0.2*150 = 30 mg/L bittering and for the 40 liter brew half that (15 mg/L). One mg/L bittering is called an IBU (international bittering unit) and it, according to the ASBC and EBC 'adequately represents the bitterness of beer'. All calculation of bitterness or done in terms of IBU. I vaguely remember something about HBU from over 20 years ago but haven't seen it even mentioned since then.

There are several spreadsheets and calculators on the net that give utilization numbers for various brewing conditions. Use one of them to calculate IBU based on whatever information you have. Hops packages are always labeled with % alpha acid but be aware that the number on the package declines over time. Also knowing what factors to use in the formulas/calculators is at best a guess so your IBU estimate cannot be counted on to be very accurate.