Filtration difficulties resulting from damage to yeast during centrifugation.

Siebert, K.J., Stenroos, L.E., Reid, D.S. and Grabowski, D.

Abstract
An investigation has been carried out to determine the reasons why, on occasions, beer centrifuged after fermentation failed to clarify satisfactorily during lagering and gave short filter runs or beer of high haze level during the final filtration through the brewery's cellulose pulp filters. Samples of beer covering a wide range of haze levels were drawn from lager tanks at the end of storage. Before and after high speed centrifugation (Sorvall RC-2B, DuPont Instruments) beer haze was measured using a Coleman Nephelocolorimeter and a Coulter Counter used to measure particle size distribution. Stained samples of haze were examined microscopically under brightfield illumination and the centrifuged haze analysed for reducing and non-reducing sugars and for protein. The non- reducing sugars were found by HPLC analysis to be almost entirely mannan. The investigation revealed that difficulties in clarification and filtration were caused by the fracturing of yeast cells during disc centrifugation, possibly the result of shearing action in the Alfa-Laval FEUX disc stack. Increases were made in the centrifuge feed rates and although the resulting beer had more haze than usual, the formation of yeast cell wall particles was reduced and there was, as a consequence, an improvement in sedimentation rate and filtration throughput.
Keywords : beer centrifugation counting filtration haze particle size yeast