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A Method for the Determination of Hop Diastatic Power – Part 2
P. C. Wietstock, F. Winter, D. Michalek, M. Biendl and B. Gibson

In the first part of this work, a method for the quantification of the diastatic activity of hops using potato starch was developed and assay conditions were optimized. In this work, other substrates (corn starch, wheat starch, rice starch, maltodextrin, dextrin, and amylopectin) were tested for their suitability to serve as substrates using 17 different pelletized hop samples from crop 2020. In addition to potato starch, dextrin and maltodextrin were selected for further testing and results were compared to data from trials involving incubation of Pilsner beer with hops. Additionally, measuring hop α-amylase, β-amylase, and amyloglucosidase activities with enzymatic test kits revealed that hop β-amylase activity correlated highest with the diastatic activity as measured using potato starch (r = 0.829, p < 0.0001), followed by maltodextrin (r = 0.655, p = 0.0004) and beer (r = 0.578, p = 0.015). Potato starch results likewise showed the highest Pearson coefficient of correlation (r = 0.853, p < 0.001) and a coefficient of determination of R2 = 0.727 with the release of fermentable sugars in beer. Maltodextrin results also showed a significant correlation with diastatic activity in beer, but at a lower level with r = 0.602, p = 0.010, while the dextrin correlation was insignificant at α = 0.05. Potato starch was therefore confirmed to be the most suitable substrate. Additional trials comparing enzymatic activities in unpelletized and pelletized hop samples showed that pelletizing has no considerable effect on hop enzymatic activity. Taken together, these data suggest that determining hop diastatic activity using potato starch appears to show the best results. This method can therefore be recommended for measuring the diastatic power of hops.

Descriptors: hops, hop creep, amylases, diastatic activity, enzymes

BrewingScience, 75 (May/June 2022), pp. 37-43