Wild yeast

Any mixture of the thousands of yeast strains which may be airborne or on the fruit, exclusive of the cultured yeast deliberately added to a must or wort. Grapes, fruit and the air often contain spoilage bacteria, molds or yeast which can destroy a beer or wine's quality, but if no spoilage yeast or bacteria are present in the must the fermentation can produce an acceptable product. Due to the risk from spoilage organisms, prudent winemakers treat their must with an aseptic dose of sulfite to kill non-yeast organisms, stun wild yeasts into temporary inactivity, and thereby allow their own choice of cultured yeast to dominate the fermentation.