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Tech. Q. Master Brew. Assoc. Am., 1994, 31(4), 146-148.

The use of radio frequency capacitance for the measurement of yeast viable biomass and its use in the automatic pitching of fermentations.

Maca, H.W., Barney, M., Goetzke, G., Daniels, D. and Ryder, D.

An evaluation of the Aber Instruments "316B", a device which uses the measurement of the capacitance resulting from passing a radio frequency through a yeast suspension to count the viable cells, is described. Comparative testing against a technique based on staining dead cells with methylene blue (methods "Yeast-3A" and "Yeast-4" in ASBC Methods of Analysis) showed that the instrument's viable cell counts were very closely correlated (r = 0.9878) with the results of the reference method. When used to calculate the volume of yeast slurry required to achieve a specified pitching rate (in terms of viable cells per unit of pitched wort volume) the instrument proved to be more consistently accurate than a "spin down wet solids estimation" technique, since the latter method is sometimes subject to interference from trub and/or continued cell death during the interval between sample collection and analysis, either of which can distort the results. Since completing the trials described, the instrument has been used for on-line yeast counting for pitching rate control purposes in a commercial brewery, where it has achieved a consistently high standard of accuracy up to the time of writing.
Keywords : automatic dosage measurement on-line pitching yeast process control sensor viability