My recipe calls for 0.5 oz. (2 AAU) Hallertau for boiling, 0.5 oz. (2 AAU) Hallertau for flavor, and 0.25 oz. (1.25 AAU) Saaz for aroma.
The problem is I don't have enough Hallertau. The recipe assumes a 4% aa rating, but mine are only 2.8%.
I have enough for the boiling stage, so would it be possible to make up the remaining AAU with Saaz in the flavor stage? That would be 50-60% Saaz instead of Hallertau.
One more question...is it even important to consider AAUs except for the boiling hops? For example, for aroma should I go with 0.25 oz. or 1.25 AAU of Saaz? Does a weaker aa rating mean only the alpha acids in that batch are low, or does it also say something about the general "power" of the hops (oil content and so on)?
The table I have says that the conversion rate to iso-alpha acids is 30% in the boiling stage, 21% flavor stage and 10% aroma stage. I didn't realize that the flavor and aroma hops added that much to the bitterness. I thought it was negligable.