A sustainable valorisation of spent hops from dry-hopping

The study aimed to evaluate the non-volatile and volatile compounds retained in the spent hop (SH) and their brewing potential carrying out brewing tests at laboratory and pilot scale with SH and fresh hops (FH). The SH, after dry-hopping (DH), were collected and stored under vacuum at -25 °C before analysis. The volatile compounds of hop oil and the hop-derived aroma compounds in wort and beer were determined. Also, sensory analysis and triangle test was performed by trained panel. The extraction efficiency during static DH was low (18.8%) and SH still contains a significant amount of hop oil. The SH showed on average lower monoterpenes and terpene alcohols content than FH, while sesquiterpenes were similar. The use of SH in wort production at the pilot scale underlined no differences in α-acids isomerization rate compared with FH. The beers, similar for the main qualitative parameters, showed differences in the polyphenol content and in the amount and composition of the hop volatile compounds. The sensory evaluation did not highlight significant differences between samples, as confirmed by the triangle test. Results clearly indicate the suitability of SH for brewing purposes.