Stability of the hop bitter acids during long-term storage of cones with different maturity degree – Urszula Skomra, Marta Koziara-Ciupa
The aim of the study was to assess the dynamics of changes in the content of hop bitter acids during long-term storage of cones that vary in maturity degree under different temperature conditions. The impact of the degree of maturity of hop cones on the stability of bitter acids during storage is little known so far, and it is important, because due to the systematic increase of the hop growing area on individual farms, the cone harvesting period is extended beyond the optimal phase of technological maturity. Hop cultivars belonging to two groups were included in the study: bitter (Magnat, Magnum) and aroma (Puławski, Sybilla). Cones were collected on a few dates during
vegetation season, starting from the phase in which they reached maximum size until the beginning of physiological maturity. The dried cones were stored at +5 °C and +20 °C for 12 months and tested every three months for alpha and beta acid content using HPLC. Studies have shown that too early a hop harvest adversely affected bitter acid content. Storage temperature had significant impact on the degradation of alpha and beta acids. At a higher temperature the decrease in the content of these compounds was greater. The tested hop cultivars were characterized by different stability of bitter acids. The highest stability of alpha acids was observed for Sybilla, while the lowest for Magnat. The stability of alpha and beta acids during long-term storage of the raw material, especially at + 20oC, depended on the degree of cones maturity. The aging rate of hop cones was not the same throughout the storage period. For the first 3–6 months at a temperature of +5oC, the bitter acid content remained at a level similar to the initial one, later a relatively rapid decrease in the content of these metabolites occurred. At higher temperatures, the bitter acid stabilization period was shorter.
Keywords: hop, alpha acids, beta acids, storage temperature, cones maturity