[Contamination of Bulgarian yogurt with yeasts and molds and the dynamics of their development in the product].

Twenty one complex production experiments aiming to establish the sources of Bulgarian yoghourt contamination with yeasts and moulds were carried out. It was established that they enter the product by way of unclean production lines and implements, by the fermenting agent, by the air in the fermentation premises. Their number in the ready product increases during storage. The extent of their increase is in relation with their initial number and with the type of yoghourt cooling and storage. At temperature 8-10 degrees C yeast numbers increase after 6-day storage from 1 500 to 4 000 times, while at temperature 18-25 degrees C even on the 3d day their number surpasses 1-15 millions per g. Moulds appear after 2-4 days of storage at 18-25 degrees C in quantities of 2000-13 000/g, while at 8-10 degrees C--after the 5th day and their number varies from 100 to 2 000/g. Defects in the organoleptic indices of yoghourt (acid-tart yeast taste and "rising") appear in case of accumulation of more than 500 000-1 million yeasts per g. In 3.5% of the 201 lots of yoghourt presented for sale on the market and investigated the presence of yeasts was established, while only one lot had moulds. Standards concerning the permissible yeast and mould content are presented, which guarantee longer periods of preservation time for Bulgarian yoghourt.