The recent amalgamation of a number of brewing companies and the continued increase in national and international franchise/contract brewing has resulted in brewing companies and individual breweries handling an ever increasing number of yeast strains. Genetically stable, aseptic and confidential storage of a master culture of each yeast strain is essential. It is common practice for brewery yeast cultures to be used to pitch fermentations a maximum of ten times. Centrally held master cultures are used to supply fresh yeast for brewery propagation and subsequent fermentations. The method of choice for long term yeast strain storage is under liquid nitrogen, a method that has been used by Scottish Courage Brewing Ltd since 1983. Master cultures were selected from existing brewery yeast populations after undergoing a range of microbiological, biochemical and fermentation tests. Other strains have been supplied by franchise partners. The poster will describe the 'cascade' system used by Scottish Courage for the storage of its brewing yeast strains. Agar slopes (slants) made from master cultures are prepared and quality assured following ISO 9000 accredited methodology. Batches of approximately 20 slopes are made from each liquid nitrogen straw, and a sacrificed slope undergoes testing for microbiological contamination, viability and yeast mutants (petites). In addition, the identity of each batch of slopes is confirmed using molecular biology analysis techniques such as PCR. Duplicate cultures of all yeast strains are held confidentially by the National Collection of Yeast Cultures as a back-up. In all, twelve brewing yeast strain master cultures are held under liquid nitrogen at the Scottish Courage Technical Centre in Edinburgh, and are used to supply ten breweries with over 600 agar slopes between them on an annual basis. The yeast storage and supply management systems in place have proved to be robust and reliable over a number of years, giving the breweries in the group confidence in the quality of the yeast supplied to initiate brewery propagations.