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Samples (29) of natural whey starters used in the Santa Fe (Argentina) area for hard cheese production were examined. The microbial composition (including lactic microflora identification) and technological characteristics (acidifying and proteolytic activities) were determined. The cultures consisted mainly of thermophilic lactic acid bacteria belonging to the genus Lactobacillus. L. helveticus (66% the total strains) and L. delbrueckii subsp. lactis (33%) were the dominant species. In every sample, yeasts appeared as the only natural contaminants, at variable contents. The samples showed high acidity levels (1.2 to 1.4% lactic acid) with a mean pH value of 3.3. The acidifying and proteolytic activities were high at temperatures ranging from 37 to 50°C and negligible at 55°C.

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