A sustainable valorisation of spent hops from dry-hopping

Dry-hopping is the cold extraction of non-volatile and volatile compounds from hops into beer and it impacts the costs per hectolitre of beer production generating a considerable amount of waste (spent hop, SH) which still contains compounds that can be reused in brewing. The study aimed to evaluate the non-volatile and volatile compounds retained in the SH and their brewing potential carrying out brewing tests at laboratory and pilot scale with spent and new fresh hops. The results highlighted that the use of SH in wort production at the pilot scale underlined no differences in alpha-acids isomerization rate (25.20%) compared with the fresh hop, FH (24.84%). The wort produced showed higher monoterpenes and sesquiterpenes levels and lower terpene alcohols. The 30 IBU (International Bitterness Units) beers, similar for the main qualitative parameters, showed significant differences in the polyphenol content (260 and 229 mg/l for FH and SH, respectively) and in the amount and composition of the hop volatile compounds (451 and 243 mu g/l for FH and SH, respectively), lower in SH samples; however, 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.