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Wine has an unpleasant sour-milk taste

If wine has acquired an unpleasant sour-milk taste, the culprit is lactic taint – a Lactobacillus or Pediococcus bacterial infection – originating from a number of sources including previously contaminated equipment, possibly from contact with spoiled and contaminated wine, or damaged grapes. The bacteria can multiply easily in wine under favorable environmental conditions and, at high levels, they will compromise the quality of the wine. Bacteria can also nestle in nooks and crannies of equipment that are difficult to clean, such as pumps, hoses and barrels, as well as in poorly sanitized equipment, such as carboys and tanks. Lactic taint is often accompanied by a vinegary smell as acetic acid bacteria (Acetobacter) are a by-product of the bacterial infection.

Possible Causes

Corrective Actions, if any

Lactobacillus or Pediococcus bacterial infection

If wine is drinkable, sulfite and stabilize filter; otherwise, dump the wine.

If the taste and smell are tolerable, sulfite and stabilize filter the wine, and drink as soon as possible; otherwise, if the taint is pronounced, the wine may need to be dumped.

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