How to calculate alpha acid levels of hops before harvesting
In addition to dry matter testing, it is important to determine alpha acid levels before harvesting hops.
A recent Michigan State University Extension article on determining harvest time, “Harvest time approaching for hop growers,” details the process needed to determine the dry matter content of your hops to determine whether or not they have reached maturity. This is important to help ensure that essential oils have developed sufficiently. Additionally, before breweries will buy your hops, they will also want to know what the alpha acid levels are.
Before hops are harvested, you will want to determine that the alpha acids have reached the targeted value expected for the cultivar. Typically, sample of fresh cones are sent to a lab for analysis to determine alpha and beta acids. Fresh hops are generally dried down to 8-10 percent moisture to prevent spoilage.
Here is a formula to convert alpha acid and beta acid concentrations derived from analysis of wet hops to estimated dry hop concentrations at 10 percent moisture:
Tested acid value x [90/(100-percent moisture)]
Actual dry hop values may be different and will need to be tested to ensure accuracy, but the estimated values will help to determine whether or not the hops are ready to harvest. To use this formula, you will need the tested values for alpha acids, beta acids and the percent moisture in the test sample. Thanks to KAR Laboratories, Inc. for providing the formula.
For an article with sample calculations and a list of laboratories that offer testing, go to “Determining when hops are ready to harvest.”