Describe how to prevent yeast growth in food.

1. Water -- Most yeast grow best with a plentiful supply of available moisture. Many yeast are capable of growing in foods that contain high levels of sugar or salt. The water requirement of yeast is generally less than bacteria but more than molds.
2. Food/Nutrients -- Yeast can grow in a variety of foods but grow best in foods that contain carbohydrates (sugar and starch) and acid. They also need nitrogen and several minerals to grow properly. Given these optimum conditions, yeast usually produce carbon dioxide and ethyl alcohol which make them very important to the food industry.
3. Oxygen -- Yeast grow best in the presence of oxygen (aerobically) but some fermentative yeast can grow slowly without oxygen (anaerobically).
4. Temperature -- Yeast can grow over a wide temperature range from 32°F to 117°F with the optimum for most yeast being between 68°F and 86°F. Disease producing varieties grow well between 86°F and 98.6°F. Yeast are easily destroyed by heat.
5. pH -- Most yeast grow best in an acid environment. They prefer a pH of 4.0 to 4.5 and lower and do not grow well in alkaline (above pH 7.0) conditions.

If you have questions, contact Dr. Angela Fraser, Associate Professor/Food Safety Education Specialist, Clemson University, Clemson, SC.

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