Effect of Floor Germination Temperature on Dimethyl Sulphide Precursors Present in Malt and Sensory Characteristics of Beer

Beer is one of the oldest beverages widely produced and consumed throughout the world. The brewing process involves at a minimum the use of the raw materials water, malt, hops and yeast (1). All of these ingredients play key roles in imparting a characteristic flavour to beer. Commercialization of beer increased significantly during the 19th century which led to expansion of malthouses, and floor malting was replaced by the pneumatic system, a batch process with controlled temperature and humidity variables. Lately with rising popularity of craft brewing, floor malting, has now been termed as craft malting. There are a few craft malt-houses around the country that have developed specific malting regimes. In floor malting, barley grains are germinated on a floor of the malthouse with no forced airflow (2). However, the consistency of malt and its influence on beer chemistry and flavor has not been determined substantially. Dimethyl sulfide is a overcooked cabbage-like off flavor sometimes found in commercial beers ranging from 5-100 μg/L (3). Kavanaugh et al., (4) established that higher germination temperatures favour proteolysis in malt, which results in increased dimethyl sulfide formation in malt. Subsequently, White and Parsons (57) argued that barley germination yields in production of two DMSP’s, one inactive and another active which form DMS in two different routes. The inactive precursor, s-methyl methionine (SMM) undergoes thermal degradation during kilning (> ~75oC) while the active precursor known as dimethyl sulfoxide (DMSO) is metabolized by yeast to form DMS during wort fermentation. This flavour defect can be eliminated from beer by modifying malt germination temperatures, increasing kilning temperature (>60oC) and by increasing wort boiling vigour and boiling times. It could be expected that after implementation of these measures most of the DMS will evaporate. However, in some cases (e.g., a short wort boil) the finished product may still have detectable DMS. Brewers select their malt fastidiously to obtain high yield extract and to avoid off-flavour in their final product. The presence of DMS in final beers can incur high energy costs (for removal) and result in decline in sales. Extensive wort boiling may not be feasible for all breweries. Meilgaard (6) reported that DMS thresholds vary with beer’s chemical composition and preexisting DMS concentration. Previous research has delineated a relationship between high germination temperature and DMSP generation. No information reporting the influence of uncontrolled germination temperature of floor malt on dimethyl sulfide precursors has been published. Hence, this thesis was directed to 1) analyze DMSP levels in floor malt samples germinated at three different temperatures and 2) evaluate DMS take-off threshold in beer made from floor malt.