THE SIGNIFICANCE OF THE USE OF HOPS IN REGARD TO THE BIOLOGICAL STABILITY OF BEER. II. THE DEVELOPMENT OF RESISTANCE TO HOP RESINS BY STRAINS OF LACTOBACILLI

Abstract

Resistance to humulone develops rapidly in a number of strains of lactobacilli, 2–4 subcultures being required to increase resistance 8–20 fold to a value of greater than 100 μg./ml. humulone, depending upon the strain. Increased resistance towards isohumulone A develops similarly. Resistant populations retain a degree of stability upon subculture in the absence of humulone. This suggests that selection of resistant mutants contributes to the development of humulone-resistance. The humulone-resistant strains possess increased powers of infection of beer over the parents from which they were derived. In these laboratory trials it was necessary to increase the hop rate by not less than 50% in order to augment the antibacterial potency of the resulting beers.