This profile provides a brief introduction to the yeast production industry with particular emphasis on the production of baker's yeast. Yeast can be obtained either as the primary product of a process, as in the case of baker's yeast, or as a secondary or by-product from alcoholic fermentations. Secondary yeast is usually preferred to primary yeast for use as animal feed for reasons of economy. Carbohydrates in the form of molasses or hydrolysed starches are the most commonly used substrates for yeast growth. Carbohydrate-containing waste streams from other processes and n-paraffins from oil have also been exploited for the production of feed yeast. Processes for the production of primary yeast vary but basically consist of materials preparation, seed yeast production, fermentation, yeast separation and pressing or drying steps, depending on the type of yeast required. About half a million tonnes are thought to be produced annually, slightly under half as baker's yeast. The size of plant can vary from half a tonne per day upwards. Plants have been built for n-paraffin feed yeast with capacities of 100,000 tonnes per year. The cost of a basic plant to produce 7.5 tonnes of active dried baker's yeast (10% moisture) per day would be about £3.5 million f.o.b. UK in July 1980. Additional plant, necessary in many locations, would increase the cost. Yeast plants are not labour intensive; this scale of operation would provide 21-24 jobs. Detailed feasibility studies should be undertaken to follow up this introduction where it is felt circumstances might be favourable
