Since grapes can spontaneously ferment without the winemaker adding any yeasts, why doesn’t a box of raisins ferment?

February 20, 2026

Dear Karen: Since grapes can spontaneously ferment without the winemaker adding any yeasts, why doesn’t a box of raisins ferment? The following content is accessible for members only, please sign in.

Dear Stan: Great question. Raisins actually can ferment on their own. In fact, sun-dried raisins in particular have many more yeasts and microbes clinging to them than fresh grapes. In antiquity, wine was probably made by soaking sun-dried raisins in a bit of water and allowing the yeasts on the raisins to convert the sugar in the raisins to alcohol. Most store-bought raisins are coated with a bit of oil to help prevent them from sticking. That coating effectively blocks fermentation.

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