Basic Effects of Sulfur Dioxide on Yeast Growth

¹ California Wine Association

1. Ricard's work showed that yeast spores of the Saccharomyces-type appear to be resistant forms that can withstand a high concentration of SO₂ for considerable length of tlme without destroying ability to germinate. This aroused some curiosity as to the ability of vegetative yeast cells to withstand SO₂. Yeast cells freshly removed from growing cultures were sensitive to relatively low concentrations of SO₂.

2. The wine spoilage type yeasts tested proved to be much less resistant to SO₂ than was the Saccharomyces-type. This is of interest because the spoilage type yeasts are primarily oxidative in metabolism, while the Saccharomyces-type used is both oxidative and strongly fermentative.

3. The pH range found in California wines has no appreciable effect in varying the action of SO₂ on the Saccharomyces-type yeast.

4. It was found that the Saccharomyces-type cells absorbed measurable amounts of SO₂, some of which was given up when the exposed cells were placed in SO₂ free water. Cells made apparently nonviable by the SO₂ treatment up to 2 hours'exposure were not revived by washing with water. The effect of sufficient amounts of SO₂ is nonreversibly inhibitory after 2 hours.

5. The data indicate that water solutions containing relatively small concentrations of SO₂ are useful in winery sanitation such as cleaning equipment. Large numbers of yeast spores, however, may survive the application of SO₂. The concentration of SO₂ which will prevent yeast spore germination is not known.

6. The idea that relatively small concentrations of SO₂ in must are effective in destroying the activity of oxidative spoilage yeasts is supported by this data.