Wine Making.
Wine is an alcoholic beverage made from fermented grapes or other fruits. Due to the natural chemical balance, grapes ferment, without the addition of sugars, acids, enzymes, water or other nutrients. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide. Different varieties of grapes and strains of yeast produce different styles of wine.
The earliest form of grape based fermented drink however, was found 9000 year old wine pottery jars in northern China. 8000 year old wine jars was found in Republic of Georgia, 7000 old jars found in Iran and 6100 year old jars found in America.
Wine plays important role in religion. Red wine is associated with blood by the ancient Egyptians.
Winemaking is also called Vilification, is the production of wine, starting with selection of the grapes or other fruits produce and ending with bottling the finished wine.
Winemaking is divided into two categories.
1) Wine production without carbonation.
2) Wine production with carbonation (natural or injected) called sparking wine or shampine.
Process:
1) Red wine is made from the must (pulp) of black or red grape skins, which gives the wine it's colour.
2) White wine is made by fermenting which is made by pressing crushed grapes to extract a juice, the white grapes are used.
3) Rose wines are either made from red grapes where the juice is allowed to stay in contact with dark skins long enough to pick up pinkish colour.
To start primary fermentation yeast may be added to the must for the red wine or may occur naturally as ambient yeaston the grapes or in the air. Yeast may be added to the juice for white wine. During this fermentation, which often takes between one and two weeks, the yeast convert the most of the sugars in the grape juice into ethanol (alcohol) and CO2. The CO2 is lost to the atmosphere.
After the primary fermentation of red grapes the free run wine is pumped of into tanks and skins are pressed to extract the remaining juice and wine. The press wine is blended with the free run wine at the winemakers discretion. The wine is kept warm and the remaining sugar are converted into alcohol and carbon dioxide.
The next process in the making of red wine is malo-lactic conversion. This is bacterial process which converts malic acid to 'soft creamy' lactic acid softing the test of the wine. Red wine some times transferred to oak barrels to mature for a period of weeks or months, this practice imparts oak aromas some tannin to the wine. The wine must selted and clarified and adjustments made prior to bottling.
Variation on the above procedure exist with sparkling wines, an additional "secondary" fermentation takes place inside the bottle dissolving trapped CO2 in the wine and creating characteristics bubles. Sweet wines are made by arresting fermentation before all sugar has been converted into ethanol, and allowing some residual sugar to remain. This can be done by chilling the wine and adding sulphur and other allowable additives to inhibit yeast activity or sterile filtering the wine to remove all yeast and bacteria.
In the case of sweet wines, initial sugar concentrations are increased by harvesting late, freezing the grapes to concentrate sugar (ice wine) allowing botrytis cineria fungus to dehydrte the grapes or allowing the grapes on racks or straw mats. Often in these high sugar wines the fermentation stops naturally as high concentration of sugar and rising concentration of ethanol retard the yeast activity. Similarly in fortified wines, such as port wibe, high proof neutral grape spirit (brandy) is added to arrest the ferment and adjust the alcohol content when the desired sugar level has been reached.
*The grapes-
The quality of grapes determines the quality of wine more than any other factor. Grape quality is affected by variety as well as weather during the growing season, soil minerals and acidity time of the harvest and pruning method.
Steps in wine making:
1) Harvesting and destemming:
Harvest is the picking of the grapes which is the first step in wine production. Grapes are either harvested mechanically or by hand. The decision to harvest grapes is typically made by the winemaker and informed by the level of sugar (called °Brix), acid (TA or Titrable Acidity as expressed by tartaric acid equivalents) and pH of the grapes. Other considerations include ripeness, berry flavor, tannin development (seed colour and test).
2) Crushing and primary (alcoholic) fermentation:
Crushing is the process when gently squeezing the barries and breaking the skins to start to liberate the contents of the berries. Destemming is the process of removing the grapes from the rachis (the stem which hold the grapes). In larger wineries, a mechanical crusher and destemmer is used.
Generally when making white wine the fruit is only crushed the stems are then placed in the press with the barries. For Red winemaking, stems of the grapes are usually removed before fermentation since the stems have a relatively high tannin content. In addition to tannin they can also give the wide a vegetal aroma.
3) Pressing:
Pressing is the act of applying pressure or promac in order to separate juice or wine from grapes and grape skins. Pressing is not always a necessary act in wine making, if grapes are crushed there is considerable amount of juice immediately liberated (called free-run juice) is of a higher quality than the press juice. Most of wineries do use pressures in order to increase their production. (15-30% more) per ton. Pressures which separates the streams of pressed juice, called making "press cuts".
As the pressure increases the amount of tannin extracted from the skins into the juice increases, whereas tannins are found primarily in the skin and seeds, due to which wine tends to be lower in actually with a higher pH than free-run juice. Now a day modern mechanical basket presses are used.
With red wines, the must be pressed after primary fermentation, which separates the skins and other solid matter from liquid. With white wine, the liquid is separated from the must before fermentation. With rose wine the skins may be kept in contact for shorter period to give colour to the wine. After a period in which the wine stands or ages, the wine is separated from dead yeast and any solid. Then it is transferred to a new container where any additional fermentation may take place.
4) Pigease:
Pigease is French winemaking term for the additional stomping of grapes in open fermentation tank. In this process certain type of wine grapes are crushed and pour into open fermentation tanks. During fermentation process CO2 gases are released. The layer of skins and other solid is known as the cap. As the skins and the source of the tannins, the cap needs to be mixed through the liquid each day or "punched" which is traditionally done by stomping through the vat.
5) Cold Stabilization:
Cold stabilization is a process used in winemaking to reduce the tartarate crystals in wine. These tartarate crystals look like grains of clear sand and is known as "wine crystals" Or "wine diamonds". They are formed by union of tartaric acid and potassium and appear to be sediment in the wine. During the cold stabilzing process after fermentation, the temperature of the wine is dropped to close to freezing for 1 or 2 weeks.
This will cause crystals to separate from the wine and stick to the side of the holding vessel. When wine is drained from the vessels, the tartarate left behind. They may also form in wine bottles that have been stored under cold condition.
6) Secondary fermentation and bulk aging:
During the secondary fermentation and aging process, which takes three to six months, the fermentation continues very slowly. The wine is kept under an air lock to protect the wine from oxidation. Proteins from the grapes are allowed to settle. Po
Potassium bi-tartarate will also precipitate, a process which cam be enhanced by cold stabilization to prevent the apperance of tartarate crystals after bottling, cloudy wine becomes clear. This fermentation takes place in either large stainless steel vessels or oak barrels.
7) Malolactic Fermentation:
Malolactic fermentation occurs when lactic acid bacteria metabolize malic acid and produce lactic acid and CO2. This is carried out in which specially cultivated strains of such bacteria are introduced into the maturing wine. This fermentation improve the test of wine that has high level of malic acid.
Malolactic fermentation increase the pH of wine. This should be monitored and not allowed to rise above pH of 3.55 for white wine and pH of 3.80 for Red wine.
8) Laboratory tests:
Whether the wine is aging in tanks or barrels, test are run periodically in laboratory to check the status of wine. Common test include °Brix. It is usually measured with a refractometer or hydrometer. pH, titrable acidity, residual sugar, available or free sulphur, volatile acidity, total sulphur and present alcohol etc.
9)Blending and fining:
Different batches of wine can be mixed before bottling in order to achieve desired taste. Fining agents are used during wine making to remove tannins and microscopic particles that could the wines.
Generally gelatin has been used to clarifying or fining wine, other fining agent for wine from animal product are potassium casseinate (cassein is milk protein), egg whites, egg albumin, lysozyme, skin milk powder and bone char.
10) Preservatives:
The most common preservative used in wine making is sulphur dioxide, normally added in one of the forms, liquid SO2, Na or K metabisulphite. Another useful preservative is potassium sorbate. SO2 has two primary actions, firstly it is an anti-microbial agent and secondly an anti-oxidant.
Generally 100 mg per liter is added immediately after alcoholic fermentation is complete. It will have the effect of preventing or stopping malolactic fermentation, bacterial spoilage and help protect against damaging effect of oxygen.
11) Filtration:
The process of clarification is concern with the removal of particles, those larger than 5-10 micrometer for coarse polishing and particles larger than 1-4 micrometers for clarifying or polishing. Microbial stabilization requires filtration of at least 0.65 micrometers. However, filtration at this level may lighten a wine's colour and body.
Clarification of wine can take place naturally by putting the wine at 2°C into refrigeration.
12) Bottling:
A final dose of sulphite is added to help preserve the wine and prevent unwanted fermentation in the bottle. The wine bottles then are traditionally sealed with a cork. The final step is adding a capsule to the top of the bottle which is then heated for tight seal.
