Membrane Filtration: Survival of Brewing Microbes on the Membrane during Storage at Reduced Humidities

Abstract

The membrane filtration technique as applied in multiplant brewery quality control has been unsatisfactory because of dehydration and subsequent death of entrapped microbes during shipment (storage) of membranes. Gram-negative bacteria and lager yeast were shown to be very susceptible to such storage over five days at humidities ranging from 0 to 98%. Gram-positive brewing bacteria, however, were much more resistant over the whole range of humidity. A number of compounds were used as protective agents in an attempt to prevent dehydration and subsequent death. One of them, 4% reconstituted skim milk powder, was extremely effective in reduction of death and is now recommended as a protective washing solution for microbes collected on membranes. Use of this protective agent allows membranes to be shipped by mail in sterile Whirlpak bags under a variety of conditions with no appreciable microbial die-off.