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Tech. Q. Master Brew. Assoc. Am., 1994, 31(3), 95-100.

Comparison of exotherm and carbon dioxide measurements in brewing fermentations.

Miller, J., Patino, H., Babb, M. and Michener, W.

Carbon dioxide and heat are generated during the brewery fermentation process in quantities proportional to the amount of sugar utilized by the yeast. Carbon dioxide formation is fairly easily measured and its use as a parameter for monitoring and automatically controlling the fermentation process has been extensively studied and discussed in the literature. Monitoring the rate of heat production ("exotherm"), on the other hand, necessitates making allowances for all the other factors influencing the temperature of the fermenting wort, so that a computer is required to carry out the calculations and data analyses which this entails. A comparative study of the use of the two parameters to monitor the course of fermentation on an industrial scale, using an ultrasonic mass flowmeter (which does not cause any pressure drop) to monitor the evolved carbon dioxide leaving the fermenter, is described. The effects of wort fermentable sugars composition on the two parameters were evaluated using two worts in which glucose and maltose were the respective principal fermentable constituents. Examples of graphs plotting the progress of the two parameters over the course of the fermentation of both these worts and showing the close correlation between the two parameters, as well as between each parameter and fermentable extract utilization, are presented. The heat production monitoring technique has the advantage that it can be applied using temperature measurement and control equipment such as is already fitted to most brewery fermenters, whereas gas flowmeters and dissolved carbon dioxide sensors must be specially fitted.
Keywords : carbon dioxide fermentation heat measurement on-line