| dc.contributor.author | Kishnani, Prachi | |
| dc.date.accessioned | 2020-05-14T17:50:18Z | |
| dc.date.available | 2020-05-14T17:50:18Z | |
| dc.date.issued | 2020-05-14T17:50:18Z | |
| dc.identifier.uri | http://hdl.handle.net/10222/79203 | |
| dc.description | 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. | en_US |
| dc.description.abstract | Dimethyl sulphide in beer tends to predominate overall flavour perceptions at very low threshold values. During malting, germination temperatures of steeped barley above 20oC induce formation of DMS precursors in malt (4), which ultimately evolve to DMS during brewing. To compare the impact of floor and pneumatic germination temperatures on the development of DMSP, two-row CDC Copeland barley was floor and pneumatically malted. Additionally, through a laboratory-scale floor malting protocol, barley was germinated at 10.0, 17.5 and 25.0oC to obtain green and kilned malt and fermented wort. Lastly, 30 L pilot brews were executed with floor and pneumatic malt to evaluate DMS threshold in beer made from floor malt. It was established that floor and pneumatic malting had a significantly different (p-value < 0.05) impact on DMSP levels generated. GC analysis detected the highest DMSP levels of 41.0 + 10.3 μg/g and 10.8 + 2.8 μg/g in pneumatic and floor malt, respectively. GC analysis of green malts germinated at 10.0, 17.5 and 25.0oC revealed no significant difference (p-value > 0.05) between DMSP levels generated at any germination temperature. Following kilning of these green malt samples at 63.0oC for 24.0 hours, GC results displayed no significant difference (p-value > 0.05) between DMSP levels obtained from samples. Furthermore, No DMSP was detected in fermented wort produced from lab floor malt. Results for sensory analysis for DMS (take-off threshold) in “floor malt” beers were inconclusive. Therefore, it was suggested that floor malt germination temperature can result in production of suitable malt which is suitable for brewers to use without resulting in off flavour development in final beer. | en_US |
| dc.language.iso | en | en_US |
| dc.subject | Germination Temperature | en_US |
| dc.subject | Craft Beer | en_US |
| dc.subject | Floor Malt | en_US |
| dc.subject | Dimethyl Sulphide | en_US |
| dc.title | Effect of Floor Germination Temperature on Dimethyl Sulphide Precursors Present in Malt and Sensory Characteristics of Beer | en_US |
| dc.date.defence | 2020-05-04 | |
| dc.contributor.department | Department of Process Engineering and Applied Science | en_US |
| dc.contributor.degree | Master of Science | en_US |
| dc.contributor.external-examiner | N/A | en_US |
| dc.contributor.graduate-coordinator | Dr. Suzanne Budge | en_US |
| dc.contributor.thesis-reader | Dr. Allan Paulson | en_US |
| dc.contributor.thesis-reader | Dr. Charles Forney | en_US |
| dc.contributor.thesis-reader | Mr. Jeremy Taylor | en_US |
| dc.contributor.thesis-supervisor | Dr. Alex Speers | en_US |
| dc.contributor.ethics-approval | Not Applicable | en_US |
| dc.contributor.manuscripts | Not Applicable | en_US |
| dc.contributor.copyright-release | Not Applicable | en_US |
