Research was carried out to determine the effect of high temperature mashing, use of short time germinated malt and low gravity fermentation on the quality of sorghum beer. The objective was to produce an acceptable low alcohol opaque beer. Mashing at high temperatures of 65-80°C resulted in lower generation of fermentable sugars with the least being obtained at 80°C leading to production of low alcohol. The main reason being that although beta- and alpha- amylase enzymes are inactivated at high temperatures beta-amylase is less temperature resistant than alpha-amylase. Thus the reduction in beta-amylase activity leads to reduction in the amount of fermentable sugar in the wort. The best low alcohol product was produced at 75°C. At 80°C although low alcohol was achieved than at 75°C there was the problem of poor body of the beer. On the other hand malt germinated for shorter period of time produced beers almost as good as those of the control brew. Only malt germinated for one day gave alcohol slightly lower than control. This shows that malt irrespective of having been germinated for 1, 2 or 3 days can produce an excellent product as long as the germination reached required levels during malting process so as to have a malt with sufficient diastatic power. Low gravity fermentation revealed that very low alcohol could be achieved by this method but dilution of wort meant also dilution of other beer characteristics resulting in a product which was watery and had no flavour. The major effect of diluting wort was that the content of fermentable sugars was reduced proportionally. However, the product of a 30% dilution was still acceptable since although alcohol was low, texture and flavour of the product were still reasonable. Thus mashing at 75°C, use of malt germinated for one day and method of 30% dilution can be recommended for the production of low alcohol opaque beers. / Dissertation (M Inst Agrar ( Food Processing))--University of Pretoria, 2006. / Food Science / unrestricted

Staling in beer is inevitable. Oxidation and increased temperatures are the main causes of stale flavors in bottled beers. Since 1934, research has been done to identify compounds and pathways involved in creating stale flavors. Although many research papers report stale flavors, there is not a lexicon per se of stale aromas for North American lagers. This study has been divided into two parts, 1) the process of developing a lexicon for stale aromas for North American lagers and its application, and 2) the use of a consumer panel to determine whether the North American lager consumer has a preference for aged versus fresh beer and whether the consumer could perceive a difference between the two. In the first study, three brands of North American lagers were aged in 27°C storage for three months and 38°C storage for two weeks. A lexicon for staling aroma for North American lagers was created, using a trained descriptive panel. The lexicon had two tiers; the first tier had five descriptors that were category headings for the second tier of descriptors. Panelists were instructed to rate the first tier descriptors, but using the descriptors in the second tier was optional. To validate the lexicon, descriptive analysis was performed on the stored samples. The data were analyzed using principal components analysis (PCA) for the first tier descriptors and generalized procrustes analysis (GPA) for the second tier descriptors. The lexicon was used successfully, characterizing the control beers as sulfury and fruity and the aged beers as sweet brown. Within the sulfury category, panelists described control beers with the attributes perm solution and skunky. Within the sweet brown category, panelists described the aged beers with the descriptors baked pineapple and honey. The beers stored at different storage temperatures behaved differently across time. The maps constructed with PCA and GPA show a tendency for control samples to start out sulfury and, through time, age with sweet brown characteristics. In the second study, a consumer panel was implemented to 1) determine if the average North American lager consumer had a preference for fresh versus stored beer, and 2) to determine if perceivable differences existed between the fresh versus stored samples. A consumer test was designed using the three North American lagers that were tested in the trained panel. The target number of consumers for each brand was 100. The aged beer was stored at 38°C for 1 and 2 weeks, and the control was stored at 1°C for that time period. A preference test, followed by a triangle test, was performed on control versus 1 week at 38°C and control versus 2 week at 38°C for each brand (2 preference and 2 triangle tests for each brand; control versus 1 week and control versus 2 weeks). The results showed no significant preference for any brand/time point. Brand A had the only significant difference (p <0.05) between samples stored at 38°C for 2 weeks and the control (The results showed no preference). Additional research must be done for more conclusive information, but this research shows that a small group of North American lager consumers do not have a preference between aged beer and fresh beer and, for the most part, cannot tell a difference between aged beer and fresh beer. / Graduation date: 2002

Malt, wort and beer samples representing a single pilot brew were extracted from Celite columns with Freon 114. Total extracts were analyzed by gas chromatography/mass spectrometry. Compounds were identified that were unique or common to beer, wort or malt and quantities present were determined for those common to the three sample types. Concentrated extracts were separated by liquid chromatography on partially deactivated silica gel packed in Teflon tubes, using Freon 11 as the solvent. Fractions from liquid chromatography were analyzed by descriptive sensory evaluation. Those fractions selected as bearing cereal-like, grassy, nutty or malty aroma characteristics were analyzed by gas chromatography. Freon extracts and fractions were found suitable for descriptive sensory evaluation and this was used to advantage in locating fractions with the desired aroma characteristics. Cereal-like, grassy, nutty or malty aroma characters were associated with liquid chromatographic fractions containing primarily alcohols, aldehydes and ketones. The Ascending Method of Limits for determination of the threshold of added substances in beer was critically reviewed and a new threshold test was developed. The new test design reduces the sample requirement from eighteen to twelve for each session. In contrast to the Ascending Method of Limits, the new test design was amenable to statistical evaluation and statement of a level of confidence for the threshold intervals determined. Both a nine-point intensity scale of difference from the labeled reference and a category scale were applied to the new test design. Intensity scale data were normalized and subjected to analysis of variance and a series of one-sided t-tests to determine individual and combined panel threshold intervals. Category scale data were analyzed by a rank sums test to determine individual thresholds and the R-index values thus obtained were subjected to analysis of variance and orthogonal contrasts of means to establish the combined panel threshold. The intensity scale method applied to the new test design provided the lowest and narrowest estimates of the threshold interval in comparative testing with the category scale method and the Ascending Method of Limits and, in addition, required fewer replications than the category scale method to establish the threshold interval. / Graduation date: 1989

The sugar composition of the wort and how these sugars are utilised by the yeast affects the organoleptic properties of the beer. To monitor the saccharides in the wort before inoculation and during fermentation is important in modern brewing industry. Reducing the duration of the brewing process is valuable and can be achieved by reducing the fermentation time by an increase in temperature. However, this must be done without changing the quality and characteristics of the end product, another incitement for proper monitoring of the wort. During fermentation, brewer´s yeast produces various by-products that affect the flavour in beer. The temperature has been reported to affect the metabolism of such compounds. In the present thesis work, monitoring with high performance chromatography of individual saccharides and ethanol was performed during a down-scaled industrial lager beer fermentation. Additionally, the effect of temperature on the fermentation rate was investigated. To determine if the metabolism of by-products was affected, a few higher alcohols and organic acids were monitored throughout the fermentation. Monitoring of degrading sugars and the production of ethanol with HPLC proved to be suitable. It is concluded that the fermentation rate is increased when the temperature is increased, however, further studies are needed to obtain more decisive results regarding secondary metabolite formation.