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Wine evaluation | What exactly is faulty wine?

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By Charl Theron

Production of Wine
The production of wine begins with the grapes in the vineyard and extends all the way to the bottle or similar container purchased by the consumer. During this period the raw material and resulting wine is exposed to a variety of different processes, conditions and managerial influences, all of which can have a significant impact on the final product. Unfortunately these influences are not always positive and can sometimes result in unacceptable characteristics, which are often described as wine faults or disorders in wine tasting. Some of the negative changes will be as a result of chemical reactions in the wine while others can be caused by certain microbes including unwanted yeasts and bacteria.

Although a variety of wine faults exist, only a few are commonly responsible for the spoilage of wine. Due to the customer demand for clear wines, the occurrence of cloudiness or sediment in wines needs to be prevented. This can be done by stabilising wines against potential precipitation or preventing the growth of unwanted microbes in the wine.

Stellenbosch University Wine CourseRole of Oxygen in Winemaking
The role of oxygen in the quality of wine is crucial and results in different approaches to winemaking. The use of oxygen in winemaking is referred to as oxidative winemaking while the prevention of any oxygen contact during the winemaking process is referred to as reductive winemaking. The overexposure of oxygen to wine leads to oxidation, which will cause changes in the colour, flavour and taste of the wine. As oxidation begins the flavour of the wine will diminish and as the process continues the colour will darken and brown. Eventually white wines will develop a honey like flavour and red wines will manifest a cooked character. Contrary to the impact of ocidation, the total prevention of oxygen exposure may lead to reductive flavours that resemble rotten eggs. A limited exposure of wine to oxygen over a long period of time is, however, positive and is an important contribution to the maturation process.

The most frequent reason for the bacterial spoilage of wine is the formation of excessive amounts of volatile acidity, which consists mainly of acetic acid. In winemaking terms it is usually referred to as the "va" of wine. It smells and taste like vinegar if present in high concentration and is one of the most basic quality control parameters used by Winemakers.

External Products
During the winemaking process wines are exposed to external products like production material, wood and bottle closures. If inferior products are used they may cause wine faults. The mouldiness of wine, as it is commonly referred, is such an example and can be smelled and tasted. It resembles the characteristics of wet soil, wet carton or mushrooms.

The prevention of wine faults is a key responsibility of winemakers and can easily be achieved by applying sound winemaking practices, chemical analyses on the wines and by using the sensory expertise of the winemaker.

This article is published under the Creative Commons Attribution license.

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