During the last 15 years sorbic acid has become widely used as a food preservative. As sorbic acid is readily available, it can be used in a number of experiments involving the use of microorganisms. These investigations can be carried out with purified sorbic acid or with raw sorbic acid extracted from rowan berries. Extracts may be prepared from fresh berries or dried berries (Fructus sorbi) purchased in pharmacies. These extracts are suitably treated with potassium hydroxide. After this treatment they show antifungal properties. Mould growth on bread and on marmalade as well as mould and yeast growth on grape-agar are inhibited. Further purification and UV examination proves that the antifungal component of the extract is identical with sorbic acid.