Use lab analysis to optimize hop harvest date

Several factors need to be considered when determining the optimum time to harvest hops.

Hop harvest.
Photo by Erin Lizotte, MSU Extension.

Hop harvest is approaching and growers often ask how to determine the optimum time for harvest. Several factors need to be considered. Cultivars have different “optimum” harvest periods; length of the optimum window varies by cultivar and by season, and hops are harvested at technical ripeness, not physiological ripeness. The best bet is to send samples for each cultivar to a lab for analysis. For an overview, see the article “Hop harvest 2016” from Michigan State University Extension.

Percent dry matter is often used as one of the primary factors to determine harvest timing. In the major U.S. hop growing regions, harvest usually occurs when cones reach an average of 22-24 percent dry matter. Growers can expect dry matter content to increase by 1 percent every four to seven days depending on variety and environment. Commercial-scale hop producers should seriously consider purchasing a table top moisture meter to determine harvest moisture and post-drying moisture levels.

While percent dry matter can provide an indication of technical ripeness, it is not the only factor that should be considered. For example, Menary and Doe (1983) found that dry matter content can vary from year to year and may not be a stand-alone indicator for optimum harvest date. Murphy and Probasco (1996) found that alpha acid levels reached a maximum level when percent dry matter was 22-24 percent. However, beta acids peaked at dry matter levels less than 22 percent, and total essential oils increased throughout the trial period.

Optimum harvest date really depends on what you are measuring and for what purpose. In addition to dry matter, growers should also consider hop quality measures (essential oils, alpha acids, H.S.I., etc.), pest pressure and weather conditions. The best way to obtain this information is to submit weekly hop samples for each cultivar or lot to a testing lab for analysis.

Many of the labs Michigan growers have used in the past are no longer offering analysis. The following list includes the current known labs offering analysis for the 2018 harvest season.

Regardless of the lab you choose, contact the lab prior to sample submission to confirm the quantity of hops needed for each test. This list is for educational purposes and is not an endorsement of those included, nor bias against those excluded.

MSU researcher seeking hop plant samples for virus testing

Carolyn Malmstrom, MSU Department of Plant Biology, is seeking samples of hop plants for developing and optimizing a diagnostic system. A large and diverse set of samples is needed. Because this is the development phase, initial assessments of virus/viroid diagnosis may be inconclusive. Grower participation will be critical to the success of this project and help improve the diagnostic protocols with the ultimate goal of developing hop virus diagnostic tools to support effective diagnosis and clean plant initiatives essential for hop industry growth and sustainability.

Sample plants that are actively or have previously exhibited symptoms of virus. You can also submit samples of plants that are failing to thrive despite adequate management, but exhibiting no visual virus leaf symptoms. Plants with an unknown issue may be infected with unknown viruses/viroids.

For more information on collection protocol, refer to “MSU seeking hop samples for virus survey” from MSU Extension.

Save the date for 2019 Great Lakes Hop and Barley Conference

Join us in Traverse City, Michigan, March 1-2 for the 2019 Great Lakes Hop and Barley Conference at the Park Place Hotel right downtown. This year will include a special focus on nutrient and water management, weed control and pruning and training in hops. If you are interested in sponsorship or vendor opportunities, contact Betsy Braid at

Please continue to visit MSU Extension’s Hop website or the MSU Hops News Facebook page for up-to-date information.

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