CONCENTRATION OF 4-MERCAPTO-4-METHYLPENTAN-2-ONE AND 3-MERCAPTOHEXAN-1-OL IN HOP CULTIVARS AND THEIR BEHAVIOR IN BREWING PROCESSES

Hop-derived thiols are believed to contribute to beer hop aroma. Here, we examined this contribution, and detected extremely strong fruity, muscat-like aromas in beers hopped with some American cultivars. The main contributor to the fruity aroma was identified as 4-mercapto-4-methylpentan-2-one (4MMP). In hop pellets, 4MMP concentrations were affected by the cultivar and copper ion content. The 4MMP content was highest in ‘Simcoe’ cultivars followed by ‘Summit’, ‘Apollo’, ‘Topaz’, ‘Cascade’ pellets. 4MMP content also differed between crop years. 4MMP was detected only in American, Australian and New Zealand cultivars, but not European ones, which are treated with Bordeaux mixture and therefore have a high content of copper ions. The field trial to spray Bordeaux mixture was conducted in the hop field of USA. The results indicated that the accumulation of the copper ion in the soil in the past years affect the higher content of copper ion in the hop cones. In the brewing process, 4MMP was found to rapidly decrease during boiling, while 3-mercaptohexan-1-ol (3MH) increased. During fermentation, both 4MMP and 3MH content increased, and 3-mercaptohexyl acetate (3MHA) was newly formed from 3MH.