Chapter 15

Wine Spoilage Microorganisms

Spoilage by Molds in Wine Prodcution

Molds are multicellular, filamentous fungi. Most are saprophytes, requiring a readily available source of exogenous nutrients. Macroscopically, mold growth appears as a mass of threadlike elements, the mycelium. Typically, a mold mycelium is composed of branched elements called hyphae. Molds are alcohol-intolerant and do not grow in wine. They may, however, be found in vineyards, especially on damaged and diseased grapes, and in wineries, where they can grow in damp environments (e.g., on wood surfaces, on walls, and floors, etc.).

Powdery Mildew

Powdery mildew can affect wine quality by imparting offflavors and other undesirable sensory qualities. The effects of powdery mildew on wine have been described as oily, viscous, fungal, or earthy.

Botrytis cinerea

Botrytis cinerea, a mold responsible for fruit rot, can be detrimental to grape quality and result in a host of secondary issues. Botrytis infected grapes can result in (1) browning due to the laccase enzyme; (2) problematic fermentations; (3) significant deterioration/reduction in total anthocyanins; and (4) post-fermentation clarity and stability problems. Acetobacter, a genus of acetic acid bacteria, is typically present in low populations on healthy berries, but its presence can increase on damaged or Botrytis-infected grapes. The main spoilage issue associated with Acetobacter is excessive production of acetic acid, which is more commonly known as vinegar.

Glucans

Lactase mediated oxidative damage is not the only problem associated with wines made from Botrytis infected grapes. Botrytis infections cause the enzymatic degradation of grape cell walls as well as production of the extracellular polysaccharide, glucan, which can cause settling and filtration issues.

Management Strategies

Although it may be difficult or impossible to control events that produce damaged or compromised fruit, there are a number of steps that you can take to minimize the impact this damage will have on wine quality.

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