wine course 3

Winecourse3


Light Wine making
 
Winecourse3 – Light Wine making
Winemaking and or vinification is equally as important as the quality of the grapes used to make good wine. In the mid 19th century, Louis Pasteur researched the fermentation process, which produces both wine and beer, and discovered that yeast, especially Saccharomyces Cerevisae, is responsible for the process. Since his discoveries winemaking has become an increasingly science and technological based procedure. Some wine producers now make wine on an industrial scale. Pasteur also researched the role of oxygen in winemaking.
1) Fermentation
In the fermentation process, yeast converts the sugars in the grape juice to alcohol and carbon dioxide. This form of fermentation, however, must occur anaerobically or in the absence of oxy gen. If yeasts are supplied with unlimited supplies of oxygen, the sugars in the grape must are converted to just water and carbon dioxide. Yeasts “prefer” to reproduce in the presence of oxygen as they can derive more energy from the sugar. The role of oxygen is, therefore, very important in wine making. For light wines, the carbon dioxide is allowed to vent into to the atmosphere.
2) Oxygen
Oxygen must be controlled at all stages in the fermentation of wine. It can destroy fruit flavours or oxidise alcohol to undesirable chemicals such as acetaldehyde or acetic acid.
Small quantities of oxygen are, however, involved in the ageing process of top quality wines. Some fortified wines such as Sherry and Madeira are produced in a deliberately oxidised process to give them their distinctive style; so if a light wine smells of Sherry or Madeira it has probably been oxidised and is faulty.
Traditional methods of wine making did not concentrate on the exclusion of oxygen. Modern methods use anaerobic techniques to exclude oxygen from most of the stages of winemaking, by use of anti-oxidants, carbon dioxide or nitrogen etc., to exclude oxygen and produce fruitier wines.
3) Light red wine production
Red wine is made predominantly from black grapes. The pigment which gives red wine its colour is contained only in the skin of the grape and not in the juice which is clear.
The grapes are de-stalked and crushed, usually, by machinery. The crushing produces the grape must and then the grape skins and must are transferred to a fermentation vat.
The must is fermented, usually, at between 20 and 32 degrees celcius.
Modern techniques use stainless steel vats to better control temperature and exclude oxygen. Traditional methods use wooden (oak) vats which allow oxygen to penetrate the must but add the tannins and oak flavour to the wine. Other types of vat are also used such as glass lined cement containers.
The period of fermentation affects the style of the wine: lighter style wines such as Beaujolais will ferment for about five days, heavier styles such as Barolo for about 10 days or longer to extract more tannin and red pigment.
When the fermentation is complete the wine is run off (“free run”) to a fresh vat. The skins are then drawn off and pressed to extract a pressed wine which is rich in pigments and tannin. This “press wine” is then blended with the “free run “wine according to the desired style.
The finished wine is then drawn off to mature in stainless steel vats or oak barrels depending on style.
Adjustments to the wine must may be made before fermentation and the wine will be racked to allow sediments to fall or fined to remove haze before maturation.
4) Light white wine production
White wine is usually made from white grapes but the juice of black grapes is clear and if their skins are removed from the must a white wine will result.
The grapes are crushed and pressed and the juice is fed to a vat without the skins. Modern methods use stainless steel vats but wooden vats are sometimes used as per red wine production.
The must is fermented at a lower temperature, usually, between 10 to 18 degrees celcius. The fermentation period is usually longer than for red wine at around 14 to 28 days. The lower temperature preserves the more delicate odours and flavours of the white wine but, also, increases the time needed for fermentation.
The finished wine is then run off to mature, either in stainless steel vats or wooden barrels according to style.
Once again adjustments may be made to the must before fermentation and the wine may be racked and fined before maturation.
5) Light Rosé Wine production
Rosé wine is made in a similar process to red wine. Black grapes are used, but some white grapes could be added to the must. The grapes are crushed and are fermented with their skins for a short period of 12 to 48 hours. The fermenting must is then run off to another vat to complete fermentation, but at a lower temperature than red wine. Press wine is not added to the final wine. The result is a wine with less colour and pigmentation than red wine.
Some bulk and cheap Rosé wine is made by blending red and white wine.
6) Maturation
Wines are matured for varying lengths of time in stainless steel vats, stainless steel barrels or oak barrels before bottling. The maturation process rests the wine and allows flavours to develop.
Oxygen is excluded from the process to prevent it from adversely affecting the wine. This means that wine matured in wooden barrels needs to be topped up to replace wine lost by evaporation. Wooden barrels allow very small amounts of air to seep into the wine but this is part of the maturation process.
Top quality wines are matured in oak barrels which impart extra flavour and tannin to the maturing product. Some commercial producers mimic this process by adding oak chips or oak staves.

 
7) Some Questions
What temperature is white wine fermented at?
Why is better quality wine matured in oak barrels?
What type of grape is used to make good quality Rosé wine.
Why can white wine be made of black grapes?
Where does the pigment which gives red wine its colour come from?
What temperature is red wine fermented at?
Why is white wine fermented at a lower temperature than red?
Name a component of “press” wine.
Why is a light wine which smells of sherry or Madeira probably faulty?
What happens if yeast is allowed to have un-limited supplies of oxygen during the fermentation process?
Name one of the undesirable chemicals produced when wine is exposed to too much oxygen.
What is the principal species of yeast used to ferment the grape must?