Die gehaltebepaling van aktiewe droë brouersgis vir bantoebierbereiding - Badenhorst, L. (University of the Free State, 1971)
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.

Hierdie ondersoek was onderneem om die gehalte van aktiewe droe brouersgis, wat in Suid-Afrika bemark word, na te gaan. Die invloed van verskeie faktore op die totale lewensvatbare gisseltelling en totale lewensvatbare "nie-kultuur" gisseltelling van aktiewe droe brouersgis is bepaal. Dit is gevind dat 99 ml fisiologiese soutoplossing, by 42°C, die geskikste rehidrasievloeistof vir aktiewe droe brouersgis is. Dit word aangetoon dat die totale lewensvatbare gisseltelling toeneem hoe langer die aktiewe droe brouersgissuspensie by temperature net laer as 42°C gehou word. Die temperatuur van die sekondere verdunningsvloeistof beinvloed nie die totale aantal lewensvatbare gisseltelling nie. Dit is gevind dat terwyl die totale gisseltelling per gram aktiewe droe gis, soos met 'n Coulter telapparaat bepaal, tussen 21,8 x 109 en 52,8 x 109 gevarieer het, het die totale lewensvatbare gisseltelling tussen 19,3 x 109 en 39,8 x 109 gevarieer. Die totale "nie-kultuur" gisseltelling per gram aktiewe droe brouersgis het tussen 11,7 x 102 en 90,2 x 105 gevarieer. Die totale lewensvatbare bakterietelling per gram aktiewe droe gis het tussen 30,0 x 102 en 12,9 x 108 gevarieer terwyl die totale suurbestande bakterietelling tussen 0 en 83,4 x 107 gevarieer het. Geeneen van die aktiewe droe gismonsters wat ondersoek is, het Escherichia coli. tipe I of asynsuurbakteriee bevat nie. Om 'n aanduiding van die aktiwiteit van aktiewe droe brouersgis te kry, is die gistingstempo daarvan bepaal. Dit is gevind dat hierdie eienskap baie van monster tot monster varieer. Die gistingstempo van aktiewe drog brouersgis is verhoog deur dit by 42°C te rehidreer. Dit word aangedui dat daar geen verband tussen die vog-, as-, stikstofinhoud, totale lewensvatbare gisseltelling en die gistingstempo van aktiewe drog brouersgis bestaan nie. Op grond van die verkree resultate is tot die gevolgtrekking gekom dat die samestelling van aktiewe drog brouersgis, soos dit die verbruiker bereik, baie varieer.
Dissertation (M.Sc.Agric. (Microbiology))--University of the Free State, 1971
Keywords: Yeast; Brewing industry -- Quality control; Beer industry -- Quality control