The analysis of chromosomes by transverse alternating field electrophoresis (TAFE) to produce a "chromosome fingerprint" for the comparison and identification of yeast strains is described together with practical applications of the technique. When the method was applied to a large collection of brewers' yeasts, it was found that while the ale strains varied considerably in their chromosome fingerprints, most lager strains fall into two groups, which the author refers to as the "Carlsberg" and "Tuborg" types after the Danish breweries from which the oldest strains of each type originated, all strains in each group having very similar fingerprints. Samples of the same commercial brewing strain, deposited in a culture collection at yearly intervals from 1958 to 1985, showed seven different fingerprints as the strain's chromosomal makeup changed over time. Interestingly, only four of the fourteen chromosomes were affected; most of the changes related to chromosomes I and VI, but chromosomes X and XI also underwent some alteration. It is thought that these chromosomes contain genes which are subjected to serious selection pressure in the brewery environment, so that changes in wort composition or in the yeast handling and fermentation processes could bring about evolutionary changes in the yeast genome. The use of the TAFE technique in the detection and identification of wild yeasts contaminating brewers' yeast cultures is also described.
Keywords : analysis brewers' yeast chromosome contamination detection electrophoresis genetics identification quality control wild yeast yeast strain