Wine evaluation | What exactly is faulty wine?
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.
Role 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.
