page_title: Clarification and stabilization of wine
section_title: Microbiological instability
hierarchical_section_title: Clarification and stabilization of wine / Stabilization / Microbiological instability
caption_attribution_description: English: Left over lees residue for Merlot wine after fermentation. Photo take Dec 2007
context_page_description: In winemaking, clarification and stabilization are the processes by which insoluble matter suspended in the wine is removed before bottling. This matter may include dead yeast cells, bacteria, tartrates, proteins, pectins, various tannins and other phenolic compounds, as well as pieces of grape skin, pulp, stems and gums. Clarification and stabilization may involve fining, filtration, centrifugation, flotation, refrigeration, pasteurization, and/or barrel maturation and racking.
context_section_description: A wine that has not been sterilized by filtration might well still contain live yeast cells and bacteria. If both alcoholic and malolactic fermentation have run to completion, and neither excessive oxygen nor Brettanomyces yeast are present, this ought to cause no problems; modern hygiene has largely eliminated spoilage by bacteria such as acetobacter, which turns wine into vinegar. If there is residual sugar, however, it may undergo secondary fermentation, creating dissolved carbon dioxide as a by-product. When the wine is opened, it will be spritzy or "sparkling". In a wine intended to be still this is regarded as a serious fault; it can even cause the bottle to explode. Similarly, a wine that has not been put through complete malolactic fermentation may undergo it in bottle, reducing its acidity, generating carbon dioxide, and adding a diacetyl butterscotch aroma. Brettanomyces yeasts add 4-ethylphenol, 4-ethylguaiacol and isovaleric acid horse-sweat aromas. These phenomena may be prevented by sterile filtration, by the addition of relatively large quantities of sulfur dioxide and sometimes sorbic acid, by mixing in alcoholic spirit to give a fortified wine of sufficient strength to kill all yeast and bacteria, or by pasteurization. 
  Pasteurization gives a kosher wine of the type called mevushal, literally "cooked" or "boiled", that can be handled by non-Jews and non-observant Jews without losing its kosher status. Typically, the wine is heated to 185°F (85°C) for a minute, then cooled to 122°F (50°C), at which temperature it remains for up to three days, killing all yeast and bacteria. It may then be allowed to cool, or be bottled "hot" and cooled by water sprays. Since pasteurization affects a wine's flavor and aging potential it is not used for premium wines. A gentler procedure known as flash pasteurization involves heating to 205°F (95°C) for a few seconds, followed by rapid cooling.
caption: Dead yeast cells can leave wine cloudy, while active yeast may trigger further fermentation.
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