Lactobacillus plantarum, the cause of yeast spots on olives.

One of the most common abnormalities associated with olives pickled in California is known throughout the industry as "yeast spots." This blemish, shown in figure 1, is characterized by the formation of raised white spots or pimples between the inner surface of the skin and the flesh of the olive. Although in general, the Sevillano variety most frequently shows this blemish, the spots may be found on all varieties and types of olives which have undergone fermentation in salt brines.' Because such olives are considered unsightly, some loss of value of the pickled fruit may be experienced, although the olives may be perfectly normal and healthful in other respects. These small white spots actually are colonies of microorganisms which have developed during the fermentation. Vaughn, Douglas and Gililland (1943) reported that most of the pimples examined in the laboratory contained lactobacilli, some cultures of which were identified as Lactobacillue plantarum. Then a deliberate search for yeasts was initiated because general use of the term "yeast spots" indicated that yeasts actually had been observed in the pimpled olives. No yeasts were found. After it was apparent that most, if not all, of the spots contained bacteria, it was decided to determine the predominating types. These investigations are described in the following pages.