So it’s time to brew your IPA again. But this year, the alpha acid content of your hops has changed. So, you jump on your brewing software, type in the new alpha acid percentages and figure out how to adjust your hop charges to hit your previous IBU target. Simple, huh?
Adjusting your hopping amounts to account for varying alpha acid content is important if you are trying to brew consistently. But keep in mind that hops supply more than bitterness (from alpha acids) to your beer — they also supply flavors and aromas from the hop oils. If your hops have 20% more alpha acids some year, your brewing software will tell you to scale back your hop additions by 20% to hit your target IBU level. However, you will also be changing the amount of hop oils added to your kettle. In turn, this will impact the aroma and flavor of your beer.
Unfortunately, the oil content of hops isn’t reported on most homebrew packaging. (It is measured and reported by hop merchants.) So homebrewers have to play a bit of a guessing game when it comes to oil content.
One easy way to adjust for varying alpha acid content, while still considering the impact on oils, is to make any IBU adjustments necessary by changing the amount of bittering hops, but leaving the level of late addition hops alone. Most of the oils from bittering hops boil away, so changing the amount of bittering hops has a smaller effect on final oil levels than changing the amount of late addition hops would have.
Getting in the habit of smelling your hops will also let you guesstimate if this year’s hops or more, less or similar in levels of aroma compared to previous years. Deficits in hop aroma can be made up by dry hopping, or even by adding hop extract, which is occasionally available at some homebrew stores.
As luck would have it, oil content seems to be correlated with alpha acid levels. In years with elevated alpha levels, oils are usually higher than average as well. The correlation isn’t perfect, but knowing this you can use the alpha levels, the aroma of the hops and your overall brewing sense to adjust the amount of late hop additions to give you the flavor and aroma you desire in your beers.