Die gehaltebepaling van aktiewe droë brouersgis vir bantoebierbereiding

[摘要] English: This investigation was undertaken to determine the quality of active dry yeast as it is produced in South Africa. The influence of various factors on the total viable yeast cell count and on the total viable non-culture yeast cell count of active dry yeast was determined. It was found that 99 ml of physiological saline at 42°C is the most suitable rehydrating agent for active dry yeast. At temperatures just below 42°C the total viable yeast cell count and total viable non-culture yeast cell count increased with the passage of time. The temperature of the liquid used for the subsequent dilutions did not influence the viable yeast cell counts. The total yeast cell count per gram of active dry yeast, as determined with a Coulter Counter, varied between 21,8 x 109 and 52,8 x 109 while the total viable yeast cell count varied between 19,3 x 109 and 39,8 x 109. The total viable nonculture yeast cell count per gram active dry yeast varied between 11,7 x 102 and 90,2 x 105. While the total viable bacteria count per gram of active dry yeast varied between 30,0 x 102 and 12,9 x 108 the total viable acid resistant bacteria count varied between 0 and 83,4 x 107. None of the active dry yeast samples analysed contained either Escherichia coli type I or acetic acid bacteria. In order to obtain an indication of the activity of active dry yeast its fermentation rate was determined. Fermentation rates varied from sample to sample. The fermentation rate of active dry yeast increased when it was rehydrated at 42°C No correlation between the moisture, ash, nitrogen content, total viable yeast cell count and fermentation rate of active dry yeast exists. From the results obtained it was concluded that the composition of active dry yeast as produced in South Africa varies considerably.

[发布机构] University of the Free State