Wine Spoilage and Defects

Wine making is fraught with risks. It can reasonably be said that as many things that can go right during wine manufacture, just as many can go wrong. The risk is exacerbated by the considerable investment that must be made to produce the wine (thus the old joke: How does one make a million dollars in the wine business? Start with $2 million). Grapes must be cultivated over several seasons before a reasonable crop can be harvested. Disease, climate, insects, and other factors can cause serious problems even before the first grape has been harvested and crushed. Once wine making begins, growth of desirable yeast and bacteria and inhibition of others is not always easy to manage. Finally, aging of wine may result in a product ranging from truly spectacular to totally undrinkable.

Spoilage of wine, like other fermented (and even non-fermented) foods, is often due to chemical and physical activities. Oxidation reactions, whether induced by oxygen, sunlight, or metals, can be especially damaging to wine, leading not only to development of off-flavors and aromas, but also to discoloration and pigmentation defects. High temperatures are also detrimental to wine quality, catalyzing chemical and biochemical reactions that result in car-amelization, browning, and oxidation reactions. Physical phenomena, such as precipitation of proteins and tannins, are responsible for cloudiness and haze formation. A particular type of haze, called casse, occurs in white wines and is caused by precipitation of metallic salts. Despite these various chemical-physical defects, however, wine spoilage is most commonly caused by microorganisms. In fact, fungi, yeasts, and bacteria can all be responsible for spoilage at some point during the wine manufacturing process.

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