To us, you are on the topic that concerned us the most since starting to brew. Hops are the biggest variable that can make or break a brew, yet it is the one variable we, the small homebrewer, have the least control over. As Wildrover says, unless you can lab test each oz you purchase, you have nothing to go by but the AA% on the package. On top of this, there are the great debates on Utilization. Do you use Rager's formula? Or maybe Garetz's? How about Tenseth's?? on and on and so fourth.
We take Ray Daniel's advice here, (author of Designing Great Beers, a book you would enjoy) He feels that we,(beer drinkers), can only perceive a 5 IBU difference in most hops. That says that if you only hit your IBU target + or - 5 IBU, you probably will not notice a difference. On Utilization, (change in IBU vs OG per oz if hops) Ray Daniels feels Rager & Garetz are on opposite extremes and Tenseth is in the middle so that is the Utilization formula he uses. Armed with these two bits of advice, we have put together our hopping scheme.
Regardless of the brewing software, or calculator method, we use Tenseth's formula for Utilization. We take great pains to develop our brewing practice and procedure so that we can be very consistent in how we brew. Then we do everything by numbers. Especially hopping. As we mention above, we first determine the BU/GU ratio of the recipe. See our earlier post. Then we stick with middle alpha hops. Ones in the 6% to 10% AA range. Most of them are hybrids of the lower IBU Noble hops so you don't give up that much in character. Also since they are higher in AA%, the variations we encounter in the AA% from season to season or whatever, are a smaller change in the total. Example a change of 2% in a 4% AA hop is a 50% change. A 2% variation in a 10% AA hop is only a 20% change. Also having a higher AA% per oz, they are more economical to use. Using our numeric ratios and basing everything on BU/GU, we can easily hit the targets within 5 IBU and hope a smarter guy than us (Ray Daniels) is right.
If we are going to duplicate someone elses recipe, we do necessarily use the hop addition weights given. We use BeerSmith and the commonly published AA% for the hop and determine the IBU of each addition and is % of total IBU. Then we make the weight changes required to hit these IBU targets with the current AA% hop.
How do you guys do it??