Wine Maturation


  • The last step in the winemaking process is bottling. A seemingly simple finale, bottling can actually cause oxidation or damage wine in other ways. Cork closures are widely used in the wine industry, but not without problems. One in 20 bottles has a faulty cork.

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  • There are several additives that can be used to prevent issues and to ensure that wine is not damaged after it leaves the winery.

    Sulfur dioxide it is almost always added to wine just before bottling because it destroys the bacteria and yeast that can cause spoilage. Because sulfur readily combines with oxygen, it helps keep wine fresh and can even reverse some of the unwanted effects of oxidation.

    Less common additives include: ascorbic acid, used for its antioxidant properties; sorbic acid, to prevent re-fermentation; metatartaric acid, to prevent tartrate crystallization; potassium ferrocyanide, to remove an iron or copper haze; citric acid and calcium phytate to remove iron; copper sulphate to reduce reduction; and gum Arabic to stabilize the wine.

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  • There are several procedures that can be used in bottling. In the first, wine is bottled unfiltered and unfined. This is an option for winemakers that have been very deliberate throughout the winemaking process. As long as the wine has been fermented to dryness and has been allowed to settle before being racked, it is possible to bottle without fining and/or filtration. If any of these conditions have not been met, spoilage may occur.

    Another option is to bottle the wine after cold sterile filtration, which involves an absolute or membrane filtration through pores small enough to exclude yeast and bacteria. To accomplish this successfully, the bottling machines must be sterilized.

    A third option is called hot bottling. This process involves heating the wine to 54°C, bottling it and allowing it to cool at room temperature. Hot bottling eliminates bacteria and yeast without pasteurization and alleviates the need for sterile conditions.

    Pasteurization can also be done at the time of bottling. One way is tunnel pasteurization in which the wine is bottled and then heated to 82°C for fifteen minutes. Flash pasteurization uses higher temperatures but shorter time.

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  • Cork failure ruins more wine than anything else. It is estimated that 5% of all wines are ruined by a faulty cork, thus one in every twenty bottles of wine is spoiled by a bad cork.

    Leaky corks can lead to infiltration of oxygen or, worse, acetic bacteria that can cause volatile acidity. A more prevalent problem is TCA contamination or corkiness. TCA is a compound that develops when mold in natural corks comes in contact with chlorine bleach during the cleaning process. TCA creates a pungent aroma that ruins the wine.

    The level of TCA contamination depends in part on how the cork was manufactured and on the quality control; expensive corks have fewer failures than cheap ones. Many alternatives to natural cork closures have been developed, such as screwcaps, synthetic and composite corks and glass closures, but none have been perfected as of yet.

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