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

Abstract
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