Study on the possibility of recycling spent hops material from dry-hopping as bittering hops (kettle addition)

Details

Supervisors

Collin, Sonia

Faculty

Faculté des bioingénieurs

Degree label

Master de spécialisation en génie brassicole

Abstract

This study sought to examine the possibility of recycling hops, previously used for their aromatic compounds during dry-hopping (Spent hops), as the source of bitter acids during the wort boiling of new brews. A preliminary study had been done as part of Schrickel, F. thesis with small-scales brews (15-kg worts) from which this research is the continuation. As part of the preliminary study, samples of hops pellets used in dry-hopped beers and their resulting spent hops were obtained from German craft brewers located in Berlin (BRLO, Lemke Berlin, Lukasz and Stone Brewing), and analyzed for their composition in bitter acids and dry matter. Retention rates in spent hops were: 31-94% for humulones, 19-92% for lupulones. For all samples, concentration of iso-humulones in the solid parts increased with dry-hopping. A set of 4 brews was produced in replicate in a 500L pilot brewery (malt pilsner, casting wort at 11,5°P): one reference brew made with a bitter hop variety (Hallertauer Magnum) and 3 brews made with different spent hops samples. For each brew, casting wort and final filtrated beer were sampled and analyzed for their bitter compounds content (humulones, isohumulones, humulinones and bitter units). The hops were dosed to provide 100 mg of bitter acids (humulones and isohumulones taken together) to the casting wort, based on the HPLC results and dry matter content previously obtained for each spent hop sample and for the HHM pellets. Analyses of the worts samples showed a bitterness of 46-54 BU, with around 34-43 mg/L of iso-humulones, 15-21 mg/L of humulinones and 1-6 mg of humulones. After fermentation, maturation and filtration, concentrations dropped by 27% for iso-humulones and humulinones and by up to 97% for humulones. The 4 first filtrated beers were assessed by a panel of 10 persons and their replicate by a panel of 8 persons (working in VLB Berlin and familiar with DLG-5-points-scheme) in their “fresh” state (bottles stowed at 6°C in a dark room) and after a forced aging (MEBAK, Eichhorn) for the quality of their bitterness, aroma and flavors (MEBAK,Kaltner). Two small-scale (4,5L) dry-hopping experiments were also conducted to study the impact of temperature, hop dosage rate and stirring velocity, on the composition of the resulting spent hops and beer after 3 days of dry-hopping. Filtered pilsner beers (3,73° and 5,3°) were used as a base for these studies. Centennial and Citra hop variety, in pellets form, were chosen for the dry hopping for their characteristic of “dual” hops (high humulones content and aromatic contribution). No sensory analyses or HPLC analyses of the oil portion were done on these trials.