A local blogger recently posted his thoughts on maintaining hoppiness when dealing with inconsistent alpha acid content of hops. What are your thoughts? Whether "right" or "wrong," i'm kinda disappointed in myself for not considering this aspect before.
When it comes to hops, brewers are mostly interested in two things: alpha acids and essential oils. In a nutshell, alpha acids provide bitterness while essential oils provide flavor and aroma. That being the case, I'm surprised by how many brewers account for seasonal variability by keeping the alpha acid contributions of each kettle addition the same from batch to batch. A better way to achieve consistent hoppiness, especially for beers where hop flavor and aroma are important, is to keep the total oil contributions of each hop addition the same from batch to batch - except for the primary bittering addition - and adjust the primary bittering addition to maintain the overall IBU level.
Suppose a brewer makes a great 5-gallon batch of IPA with the following hop bill:
1.5 oz Magnum hops, 14% alpha acids, boiled for 60 minutes -> 44 IBUs
3.9 oz Centennial hops, 8% alpha acids, added in the whirlpool -> 16 IBUs
2.0 oz Centennial hops, 8% alpha acids, dry-hopped -> 0 IBUs
The following year, the brewer wants to reproduce the batch. However, the new crop of Magnum are 12% alpha acids and the new crop of Centennial are 10% alpha acids. If the brewer tries to maintain alpha acid consistency instead of total oil consistency, the hop bill will look like this:
1.7 oz Magnum hops, 12% alpha acids, boiled for 60 minutes -> 44 IBUs
3.1 oz Centennial hops, 10% alpha acids, added in the whirlpool -> 16 IBUs
2.0 oz Centennial hops, 10% alpha acids, dry-hopped -> 0 IBUs
If the oil content of the Centennials remains constant, the beer will have fewer hop oils than the previous batch. In other words, the new batch won't be as hoppy. To compound things, the Centennial oil levels probably dropped because the alpha acid increases likely occured - at least in part - at the expense of essential oils. I'd wager that's why most bittering hop varieties don't have great flavor/aroma characteristics. Unfortunately, hop brokers don't often provide information on total oil content. Commercial brewers can ask for it (although it seems that few do), but homebrewers have less leverage because they don't buy directly from brokers. If you don't have oil data, it's fine to assume that the oil levels of a given variety will stay the same from purchase to purchase. Back to our example batch, maintaining the Centennial oil contributions of the original batch and adjusting the Magnums to compensate for IBU fluctuations will result in the following hop bill:
1.6 oz Magnum hops, 12% alpha acids, boiled for 60 minutes -> 40 IBUs
3.9 oz Centennial hops, 10% alpha acids, added in the whirlpool -> 20 IBUs
2.0 oz Centennial hops, 10% alpha acids, dry-hopped -> 0 IBUs
Note that the weights of Centennials are the same as the initial batch. That's the result of our assumption that oil levels remain constant. Keeping the weight of each late hop addition the same works well as long as you don't switch varieties. However, what if you want to use Cascade instead of Centennial but still keep the hop "intensity" the same? A good resource is the HopUnion Hop Variety Data Booklet, which you can download here. You can see that the middle value for total oil content of Centennials is 1.9 mL/100 g and the corresponding value for Cascades is 1.15 mL/100 g. To adjust the hop bill, multiply the Centennial weights by 1.9 and divide by 1.15 to end up with the following values:
1.6 oz Magnum hops, 12% alpha acids, boiled for 60 minutes -> 40 IBUs
6.4 oz Cascade hops, 6% alpha acids, added in the whirlpool -> 20 IBUs
3.3 oz Cascade hops, 6% alpha acids, dry-hopped -> 0 IBUs
Again, the Magnum addition was adjusted to maintain an overall bitterness of 60 IBUs. That's how to maintain hoppiness!
