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The impact of climatic conditions on the biogenesis of various compounds in hops
A. Forster, A. Gahr, F. Schüll and J. Bertazzoni

Climate influence on yield and α-acid content of hops is known. Systematic research on the biosynthesis of aroma substances and polyphenols in different hop varieties depending on the weather conditions are lacking. Pellet T90 samples from big lots of 11 German aroma, 4 special flavor and 5 bitter hop varieties were chosen for the study. In this respect the two consecutive crop years 2015 and 2016 were found to be very suitable for a comparison. Summer 2015 was hot and dry, so amount and alpha yield were rather poor, whereas the summer 2016 offered good conditions with enough rainfall and moderate temperatures. Subject to analysis were: α- and β-acids, xanthohumol, total polyphenols, low molecular polyphenols in five subgroups, total hop oil and 50 aroma substances that were grouped into their individual subgroups too. α- and β-acids were particularly sensitive to unfavourable conditions, in aroma varieties more than in flavor or bitter hops. However, the polyphenols were not. Aroma components show big differences in their sensitivity to climate, especially esters and epoxides. Terpenes turned out to be a bit more stable than the oxygenated fraction. Apparently, linalool content in flavour hops showed a higher resilience. The susceptibility of hop substances and hop varieties to climate conditions evidently is different. The aroma components of the bitter varieties were less affected than those of the flavour and the aroma hops especially. The knowledge, how hop compounds react differently on varying climatic conditions helps the brewers to minimize unwanted variations in aroma and beer bitterness.

Descriptors: climate change, hop compounds, climate tolerance, hop varieties, hop crop variability

BrewingScience, 74 (November/December 2021), pp. 160-171