A test method to investigate the heat resistance of yeasts has been developed. The method was used to study the heat resistance of 120 yeast strains, representative of the fungal flora in soft drinks and certain acid food products: 35 asporogenous yeast strains (Brettanomyces, Candida, Kloeckera, Rhodotorula and Torulopsis) and 85 ascomycetous strains (Debaryomyces, Hansenula, Kluyveromyces, Lodderomyces, Pichia, Saccharomyces and Saccharomycopsis) were tested. Generally, asporogenous yeasts were found to be less heat resistant than ascomycetous types. The genus Saccharomyces showed the highest heat resistance, especially strains of the species Sacch. cerevisiae and Sacch. chevalieri. For an evaluation of the practical implications of these results additional studies on environmental factors influencing the heat resistance of ascomycetous yeast species are required.

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Samples of a carbonated orange drink, raw materials, and intermediate products originating from 6 Iraqi bottling plants were examined. 69 drinks, 4 flavoured syrups and 19 simple syrups contained yeasts, whereas all samples from one plant and all samples of beverage base were free from viable yeasts. From the orange drink 2 species were isolated viz. Saccharomyces montanus and Torulopsis stellata. The following species were present in simple syrup: Hansenula anomala, Sacch. bisporus var. mellis, T. candida and T. stellata. Sacch. bisporus var. mellis was also isolated from favoured syrup. Representative strains were submitted to routine growth tests at reduced oxygen tension, at reduced water activity and on solid soft-drink media containing various amounts of anti-microbially active benzoic acid at pH 3.0. The results are discussed and compared to those obtained in European soft drinks.