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Beer Spoliage Organisms
Wild Yeast
Wild yeast is any yeast other than the pitching yeast. Wild yeasts can be isolated at all stages of the brewing process from raw materials, wort, pitching yeast, and fermenting beer, through to the packaged product and the dispense system. Wild yeast can produce unintended flavors, including hydrogen sulfide, estery, acidic, fatty acid, and phenolic or medicinal notes. Turbidity is another effect caused by growth of wild yeast that remain after the culture yeast has been removed by filtering or fining. In the presence of air, some wild yeast can grow rapidly and form a film on the surface of the beer, which can cause haze. Other effects may include primary yeast fermentation and separation difficulties, significantly lower terminal gravities, and a higher alcohol content in the finished beer. The lower terminal gravities are due to the ability of wild yeast to ferment sugars (such as maltotetraose and dextrins) not used by the primary yeast. Wild yeast infection is usually more of a problem for brewers not having a pure culture yeast propagation system than for those who do.
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