MANUFACTURING PROCESS OF STILL WINES
Any one method may be followed between two methods: Mechanically (harvesting machines), manually (Hand- Picked). Hand-picked method is very costly. The mechanically method is more efficient, cost effective and well suited for large vineyards.
Crushing and De-stemming
After harvesting, the grapes are crushed and quickly de-stemmed. Hydraulic, revolving, cylinders and the pneumatic bat press are the widely used methods of crushing grapes. Some wineries follow the old foot –pressing method. The gently crushed grapes are known as “must”.
The “must” (juice, skin, pulp and seeds) is transferred to the fermentation tank which may be a wooden or stainless steel vat. The must contains wild yeasts, wine yeasts and the acetobacter a wine-spoiled mould. With the addition of sulphur dioxide to the must, the winemaker prevents any bacterial contamination and kills the harmful wild yeasts and the vinegar forming acetobacter, moreover, the sulphur taste disappears during the maturation.
During fermentation, the unfermented must contains approximately 24% grape sugar ( to achieve 12% alcohol), along with various acids, cream of tartar, protein, tannin and minerals. If the must does not contain enough natural sugars to produce the required amount of alcohol, a small amount of sugar may be added. This is known as Chaptalization.
when the acidity is low in must, the acid can also be added, this referred to as Acidification.
During fermentation, the yeasts act on the sugar in the juice and produce carbon dioxide gas and ethyl alcohol. For red wines, the temperature is typically 22-25 degree C. fermentation stops when all the sugar is converted to alcohol or when all the yeasts are killed.
By the end of fermentation, the new wine lies in the bottom of the vat and the solid matter floats on the top. The new wine, called the vin de goutte, is racked into another vat. The solid mater is pressed to obtain vin de presse. The first batch of vin de presse is rich in tannins and flavor and may be added to the vin de goutte. The wine is then transferred to wooden vat for ageing. Some wineries use stainless steel vat for ageing which produces light red wine.
The wine is racked off its solids and placed in a container (which is often oak wood barrels), to mature. The oak may be French or American, air-dried or kiln – dried, toasted or charred. The option of wood and its make, dictate the flavor profile of the wine. During the process of ageing, the wine absorbs the vanilla flavor from the oak and interacts with the oxygen that invades through the fine pores. The oxygen eases out tannin and mellows the wine. Evaporation takes place during the wine’s life in the cask. The space must be topped up with similar wine to exclude the air and to prevent spoilage. The other option available for maturation is a stainless steel tank. Such tanks need not be replaced for years and are very easy to maintain.
During the ageing process, a secondary non-alcoholic bacterial fermentation called malolactic fermentation takes place. In this type of fermentation, the bacteria convert the harsh malic acids in the juice into softer lactic acids. This imparts a softer mouth feel and a more inviting palate. Most red wines go through malolactic fermentation to reduce their acidity.
Filtration and filling (Clarification)
Wines require clarification as they are cloudy and contain very fine particles. The clarification is obtained by filtration and fining. Filtration removes the solid matter from wines including dead yeast cells. Fining is carried out to make the wine clear and star bright. This can be achieved by adding substance, such as the white of an egg, gelatin, etc. these additions attract all the impurities ad settle at the bottom of the cask. The wine is then racked into another container to remove the sediments. Wine can also be fined through the application of centrifugal force or passing it through a series of cellular filters.
Blending is the process of mixing wines of different years, age, grapes and regions to make either a new wine with a unique flavor, or to maintain consistency in quality. A winemaker may blend wines for various reasons such as to adjust acidity, alcohol levels, tannin content, or to improve the colour, aroma and flavor. Blended wines are then rested and fined again.
After blending, the wines are bottled in sterilized bottles. The wine bottle is slowly filled and topped with either nitrogen or carbon dioxide to displace any oxygen. The bottle is then capped with either a traditional, treated cork or a modern screw cap.
This is an alternative method of making red wine. In this method, a bunch of grapes is placed in a clean container which is filled with carbon dioxide (CO2) gas, and is sealed. The container is fitted with a valve to ease out the pressure. The grapes at the bottom of the bunch get crushed by their own weight. The sugar is converted into alcohol and co2 is given off by the action of yeast present on the skin. The uncrushed grapes in the bunch undergo their own fermentation. This process produces light bodies fruity wine with low alcohol content.