wine course 4

Wine Course 4
Light Wine Making Adjustments and Bottling
 
Wine Course 4 - Light Wine Making Adjustments and Bottling
There are many adjustments and technical issues to be considered in the production of light wine, and these are discussed below.
1) Malo-lactic Conversion
Many wines, especially reds, contain too much malic acid which makes the wines taste tart. Apples contain this acid which is why they often taste sharp. To reduce the malic acid concentration, wine makers encourage the growth of bacteria, such as Lactobacillus, which convert this acid to softer tasting lactic acid. This adjustment is often called secondary fermentation and takes place in the fermentation vat before the wine is drawn off for maturation.
2) Residual sugar
The residual sugar left in the wine after fermentation determines the sweetness of the wine; either dry, medium, medium sweet or sweet:
Dry wine up to 9 grams per litre of sugar
Medium up to 18 grams per litre
Medium Sweet up to 45 grams per litre
Sweet no less than 45 grams per litre
Naturally sweet wines are produced when the fermenting must is unable to convert all the sugar into alcohol. To prevent the alcohol level from becoming too high, very sweet grapes are used in the original must; and this high level of sweetness inhibits the growth of yeast. Grapes exposed to “noble rot” contain a natural fungicide which, also, inhibits yeast growth. Cooling the wine then stops the fermentation.
3) Alcohol
Light wines are fermented to between 8% and 15% alcohol by volume depending on style. Most wine is fermented to around 12% to 14%. The level of alcohol is controlled by the amount of sugar available for fermentation, the yeasts used, the temperature and the length of time the wine is allowed to ferment. If a wine achieves a 15% level of alcohol fermentation stops.
Modern techniques can stop fermentation and alcohol production by the addition of sulphur dioxide to kill the yeast, filtering out the yeast or increasing the pressure of carbon dioxide. This can result in an unstable wine which might start to re-ferment.
4) Yeasts
Traditional fermentation used natural yeasts found on the grapes, in the air and on the surfaces of the vineyard to ferment the must.
Modern methods use yeasts cultured in the laboratory and sold as a freeze dried product or as a living culture.
Whilst cultured yeasts enable the wine maker to control fermentation better, the use of standardised yeast cultures has lead to loss of individuality of taste and standardised wines which taste the same across the world. Some winemakers are using a mixture of traditional and modern techniques.
5) Must Adjustment
Before fermentation starts, the grape must is protected by the addition sulphur dioxide which acts as a disinfectant and anti-oxidant. It is added in the form of potassium sulphite or potassium meta-bisulphite powder.
In vintages where the weather has been less than kind, the grapes may not be balanced for acids and sugars. The wine must is then adjusted by adding or removing acid from the must to control acidity Adding sugar or rectified concentrated grape must improves the sweetness of the grapes. Biochemical intervention must be controlled carefully, and in the EU is controlled by rules. There is really no substitute for using high quality grapes.
6) Racking
After fermentation is complete wines are racked to allow dead yeasts to fall to the bottom of the vat as sediment or lees. This helps to clear the wine before it is drawn off the lees for subsequent maturation. Several racking operations may be conducted throughout the maturation process.
7) Fining
Fining is used to remove haze producing colloids, in the wine, and help clarify it. The fining agents used include: egg white, gelatine, bentonite and isinglass gelatine.
8) Filtration
Filtration is not usually used for traditionally made wines, which often throw natural sediments whilst they age in the bottle.
Modern wine making techniques use coarse filtration to remove particles to clarify the wine. Membrane filters are sometimes used to remove micro-organisms and sterilise the wine.
It is a controversial subject when filtration is used for traditionally produced wines, as some commentators believe it ruins the wine.
9) Sweetening
Some commercially produced light wine is sweetened before with bottling with rectified concentrated grape must. In the European Union this is strictly controlled.
10) Bottling and other packaging
Most wine is sold in glass bottles. Glass is the best medium for storing wine when it needs to be aged before drinking. All top quality wine is bottled.
There is increasing use of “bag in the box”, cardboard “tetrapack” and plastic bottles. These add to the convenience of storing and serving the wine quickly. The wine deteriorates more quickly in this type of package which is meant for commercially produced wine. The shelf life of these products is limited and should be noted before purchase.
Whatever the form of bottling or packaging, all wine is preserved with sulphur dioxide before packaging and all containers must be completely clean and aseptic before they are filled.
11) Seals
The traditional method of sealing bottles was to use seals made of natural cork. However, the problem of cork taint, where a fungal infection caused a taste of mould to taint the wine, has converted some wine makers to use “technical corks”, plastic corks or screw caps to eliminate the cause of cork taint. It is estimated that 5% of wines sealed with natural cork are subject to cork taint.
Artificial seals also reduce the ingress of oxygen into the bottle. Screw caps are increasingly seen as being an ideal solution but they can easily get damaged in transit or on the supermarket shelf.
Natural cork is still being used to seal wines meant for ageing; as they allow very small amounts of oxygen to penetrate the wine to help it mature. This point is, however, hotly debated. Top quality wines are sealed with very long corks.
Natural cork suppliers are “fighting back” by improving cork preparation techniques to eliminate the cork taint problem.
The use of seals is hotly debated as this is where the wine actually meets the consumer after a long process. The pulling of a cork remains part of the mystique of wine consumption. Many quality wines producers will no doubt retain natural corks.
 
12) Some Questions
What happens to fermentation when the alcohol level reaches 15% by volume?
What types of yeast are used for fermentation by the traditional method?
What type of filter is used to remove particles?
What is egg white used for?
What does cork taint smell of?
What is used to sweeten some commercially produced wine?
What type of container is used for wines meant for ageing?
Why are wines racked during maturation?
What is potassium sulphite used for?
Why should a wine bottle sealed with a screw cap be examined before purchase?
What prevents a very sweet grape must from fermenting to too high a level of alcohol?