Paper Summary:

This paper describes a study to investigate the effects of an acetic acid contaminant on the ale fermentation process. It examines how contaminants are constantly introduced into samples during the brewing process, which changes the standard procedure and leads to specific effects on the final product, such as a change in aroma or flavor and how in this case, because the fermentation is carried out by yeast cells, the experiment is focused on the contaminant's effect on the yeast cells and their ability to carry out the fermentation process. It also discusses how the factors which are affected by this alteration of the wort can be monitored to determine the effects caused by inoculation of the sample.

Outline:
Abstract
Introduction
Materials & Methods
Inoculation of Wort
Results
pH
Temperature
Concentration
Discussion

From the Paper:

"Fermentation of top-feeding yeast, Saccharomyces Cereviseae, was done in conjunction with the addition of acetic acid inoculant to half of the sample. Evidence of effects from the addition of the contaminant was tested by monitoring three factors; pH, temperature and concentration of yeast cells. Two replicates of the control and contaminant models were tested after 0, 1 and 4 days from the initial inoculation of the wort sample. Fermentation of beer by S. cerevisiae occurred in both of the samples, which was evident by the change in all variables. The temperature and pH values obtained from analysis of the samples showed no significant changes; the null hypothesis was not rejected with a critical t-value greater than the calculated t-value. The concentration showed a significant change between the two samples, therefore the alternate hypothesis was accepted and the null hypothesis was rejected with a calculated t-value higher than the critical t-value. "

Sample of Sources Used:

• Bowen, R.W. and Cooke, R.J. 1989. Effect Studies of Saccharomyces cerevisiae during fermentation - an in vivo electrokinetic investigation. Biotechnology and Bioengineering 33: 706-715.
• Kobi, D., Zugmeyer, S., Potier, S., Jaquet-Gutfreund, L. 2004. Two-dimensional protein map of an "ale"-brewing yeast strain: Proteome dynamics during fermentation. FEMS yeast research 5: 213-230.
• Lekkas, C., Stewart, G.G., Hill, A.E., Taidi, B. and Hodgson, J. January 2007. Elucidation of the Role of Nitrogenous Wort Components in Yeast Fermentation. Journal of the Institute of Brewing 13: 223-232.
• Rowe, S. M., Simpson, W. J., Hammond, J. R. M.1994. Intracellular pH of yeast during brewery fermentation. Letters in Applied Microbiology 18: 135-137.
• Saerens, S., Delvaux, F., Verstrepen, K., Van Dijck, P., Thevelein, J., Delvaux, F. 2007. Parameters Affecting Ethyl Ester Production by Saccharomyces cerevisiae during Fermentation Applied and Environmental Microbiology 74: 454-461.

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