Hop Storage Index. Gail B. Nickerson and Sam T. Likens. J. Am. Soc. Brew. Chem. 37:0184, 1979.

The hop storage index (HSI) is used to estimate losses of α-acids and β-acids during storage and handling. HSI is determined from the ultraviolet absorbance measured in the spectrophotometric analysis of hops. Collaborative tests of the HSI measurement gave 1.3% within-laboratory and 2.8% between-laboratory coefficients of variation. The relationship between % (α +β) lost and HSI shows some year to year variation. The slope of the equation % (α + β) lost = slope x log (HSI/constant) was 101.8, 111.3, 114.5, and 114.6 for the 1969, 1975, 1976, and 1977 crop years, respectively. The HSI has been used in evaluating varietal differences in storage, measuring permeability and antioxidant levels in lupulin glands, determining hopping rates in breweries, and evaluating grower and dealer handling practices.

Keywords: α-Acids, β-Acids, Hop storage, Spectrophotometric analysis