Valorization of Spent Hops from Dry Hopping for Bittering of Pilsener Style Beer

Abstract

In the last decade production of dry hopped beers increased considerably. Dry hopping results in significant amounts of spent hop material (mixture of beer and hop vegetative matter), which is mostly regarded as waste and is discarded. During dry hopping polar (aroma) compounds are extracted into beer, while nonpolar compounds such as humulones largely remain in the spent hops. In this study, spent hops from local craft breweries were collected. They were analyzed towards dry matter (d.m.), surplus beer content, their concentration of humulones, and iso-humulones, and were then used as the sole source of bitterness in the production of Pilsener Style beer. It was found that humulone concentrations in spent hops ranged from 1 to 10.3% dry matter, which corresponds to retention rates of 28 to 94%. Wort and beer samples made from selected spent hop samples were analyzed using a range of physicochemical analyses, along with sensory evaluation of both fresh and aged beers. Beer analysis showed that the targeted bitterness (30 BU) was successfully achieved in most brews. Sensory analysis confirmed the good overall quality of spent hop beers as such and also in comparison with a reference brew using hop pellets. In summary, spent hops can be valorized by substituting hop pellets in the kettle, leading to reduced beer losses, savings on hop pellets, increased sustainability and hence reduction of production costs.