Ensiling of hop chaff for biogas and fibre production using molasses, nitrate and lactic acid bacteria as ensiling agents

Hop (Humulus lupulus L.) is a perennial crop primarily cultivated for brewing, generating substantial underutilized biomass. This study evaluated the ensiling of hop chaff without additives (control) and with molasses (3 % w/w), nitrate (0.43 % w/w), lactic acid bacteria (LAB; 2 × 10⁵ CFU/g), and combinations thereof. Nitrate proved most effective in stabilizing pH, reducing dry matter loss, and inhibiting clostridial fermentation. Butyric acid remained low (0.02 ± 0.02 %_TS), while silages with nitrate and molasses achieved the highest lactic acid concentrations (7.5-7.6 %_TS), compared to the control (butyric acid: 0.6 %_TS; lactic acid: 1.6 %_TS; p < 0.05). One-day open storage negatively affected fermentation. The inhibitory effects of hop chaff on biogas production were eliminated by ensiling, while Hop Latent Viroid RNA levels remained unchanged. Ensiling with nitrate is an effective approach to enhance the usability of hop residues in biogas production and other bioresource applications.