Impact of bulk weight on drying behaviour and hop quality after drying

Summary

Hops are a key ingredient for beer brewing due to their role in the creation of the foam characteristics, bitterness of the beers and aroma. Whilst in the past foam and bitterness were the key characteristics sought by the market, the last decade has seen a steep increase in demand of aroma hops for the production of crafts beers. Color of the final product plays a major role in quality perception of traders and brewers. Therefore, color changes were investigated to estimate the impact of bulk weight and thus drying time and conditions on the upper surface of the bulk. A calibrated imaging system consisting of a CCD camera and illumination was integrated into the dryer. Further, changes of  and ß acid contents were investigated. Hops of the variety Mandarina Bavaria were dried at 65°C and an air velocity of 0.35 m/s. Bulk weights investigated were 12, 20 and 40 kg/m² respectively. Drying times were 105, 135, and 195 min. Drying characteristics showed a unique development which very likely is due to the distinct physiology of hop cones (string, bracteole, bract, lupilin glands). Color changes depended strongly on the bulk weight and resulting bulk thickness whilst a and ß acid contents
were not affected by the drying conditions. The research presented showed that air mass flow in relation to the mass of water to be removed is critical for the quality of the product as well as the processing time required.