Yeasts are the initial organisms to grow on the surface of smear-ripened cheeses directly after manufacture and salting/brining. The conditions of low pH (~4.9-5.2), relatively low ripening temperature and high salt concentration on the cheese surface favour their growth. Although considerable variation occurs, the most prevalent yeasts reported in many smear cheeses include Debaryomyces hansenii, Candida spp., Trichosporon spp., Yarrowia lipolytica, Kluyveromyces spp., Rhodotorula spp. and Torulaspora spp. Geotrichum candidum is also prevalent and has the characteristics of both a yeast and a mould. A succession of different species may also occur during ripening.
Yeast growth on the cheese surface serves two functions. Firstly yeasts deacidify the cheese surface by the metabolism of lactate to C02 and H20 and by the deamination of amino acids and the production of NH3. This leads to an increase in pH of the cheese surface with the development of a pH gradient between the surface and core of the cheese. The increased pH on the cheese surface makes conditions more favourable for the growth of salt-tolerant bacteria. Deacidification is dependent on both the numbers and strains of yeasts present. Secondly, yeasts produce compounds that are stimulatory to the growth of the bacterial smear flora. These compounds include products of proteolysis and vitamins synthesised by the yeasts (e.g. pantothenic acid, niacin, riboflavin).
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