Preparation of wine involves various methods from selecting the grapes to bottling of the wine. Preparation of wine is divided into two types- still wine production (no carbonation) and sparkling wine production (carbonation). The wine grapes have to undergo numerous procedures to be made into that perfect wine craved by many.

Grapes

The most important factor required to ascertain the best quality wine is the grapes. The best quality grapes will give the finest wine. The location of vineyard, weather, acidity and minerals in the soil, time of harvest, methods of pruning, pest management play a key role in the quality of grapes. As can be derived from the names, red grapes make red wine and white grapes make white wine. Most of the best quality wine grapes originated in Europe but are now cultivated all over the world.

Harvesting

The harvesting time of grapes plays a very critical part in quality of wine. Winemaking actually commences with the annual harvesting. Harvesting is the picking of grapes which is done either by hands or by machines. The winemaker makes the decision of harvesting by taking into account the sugar, acid and pH of the grapes. The ripeness, tannin development, flavor, weather forecast and overall temperament of the vineyards are also taken into consideration.

Mechanical harvesting is done by huge tractors. They are more efficient, cost-effective and are suitable for the large vineyards. But a major disadvantage of mechanical harvesting is that it includes a lot of foreign materials other than grapes which mostly consists the leaves and stems. Sometimes it also includes moldy grapes, rocks, even bird nests and small animals. Mechanical harvesting is rarely used in the United States. It is more common in Australia and New Zealand because of the lack of labors there.

On the other hand manual harvesting is more precise and mostly does a better job of preventing the grape juice from getting oxidized. Also the labors pick only the ripe clusters and leave behind the raw or rotten grapes. Manual harvesting can increase the budget but it surely helps in retaining the quality of wine.

In the northern hemisphere grapes are usually harvested from early September to November while in Southern hemisphere they are harvested in mid February to start of March.

Destemming

The process of destemming involves the separation of stems from the grapes. The process is mostly undertaken before the crushing process to prevent the tannin development and vegetal flavors in the wine. Destemming can also be done while crushing. The process of destemming is different for white wine and red wine. While making white wine, generally, the stems are placed in the press after crushing the fruit so as to allow the juice to flow past flattened skin. On the other hand, in red wines the stems are removed before the fermentation as stems contain a significantly high tannin content. In some cases the winemaker allows to leave the stems if the grapes itself contain less tannin content.

Crushing

The process of crushing involves squeezing the grapes and splitting the grape skin to allow the juice to flow. It gives the sugar a first chance to mix with the natural yeast found on the skin of grapes. It is this combination of sugar and yeast that produces the alcohol in wine (as yeast converts the sugar into alcohol).  Crushing is also done in two ways- by mechanical spiraled steel roller crushers or the traditional stomping.

At this point the red wine grapes and white wine grapes take separate paths.  In case of red wine, it is the grape skin that provides the color characteristics and the tannin contents. But, if it is destined to be a white wine, then the skins and stems are removed at this point and the grapes are pressed before they are fermented.

Primary Fermentation

Fermentation is the process during which the grape sugar is converted into alcohol (ethyl alcohol to be specific), carbon dioxide and residual heat. Fermentation can be done with the natural yeasts present on the grape skin but it can give uncertain results so cultured yeasts are added to the “must” (grape juice). The fermentation temperature can affect the taste of the wine and also the fermentation speed. The ideal temperature for red wines is around 22 to 25 °C and 15 to 18 °C for white wines. Also around half a gram of alcohol is generated for every gram of converted sugar, so if 12% alcohol concentration is needed, the must should have 24% sugar. In case the grapes are not ripe enough, sugar can be added to maintain the level of alcohol; likewise if the acidity is low, acids can also be added.

Red wine is normally fermented in stainless steel tanks, oak barrels or large vats. During this phase a good red wine color is produced as the grape skins and must have maximum contact. The white wine fermentation is usually done in stainless steel tanks kept on low heat levels which are closely monitored and the level of oxygen is also minutely checked to prevent oxidation. For white wines an additional process, “stirring the lees” is also executed which includes mixing the yeast, left after fermentation, to generate more flavors.

Pressing

Pressing is the process in which pressure is applied to the grapes so as to separate the grape juice from the grape skins. Pressing is not a necessity in wine preparation because during the crushing process itself a significant quantity of juice is produced that can be used to prepare wine. Also this wine will make a better quality wine than the pressed juiced wine. But many wineries use pressing process to increase their wine production as pressed juice can amount an increase of 15% to 30% in the production. Pressing basically involves the squeezing of grape solids that are left after the crushing or fermentation.  Pressing of white wines is usually done after crushing while that of red wines is done after the fermentation.

Cold Stabilization

Tartrate crystal in the wine can be reduced by a process called as cold stabilization. The tartrate crystals, also called as wine crystals or wine diamonds, look like small grains of clear sand. These crystals are formed by the mixture of potassium and tartaric acid. In the cold stabilization process the temperature of the wine is reduced to freezing point for one or two weeks, during which the crystals will separate from the wine and can be found sticking to the walls of the vessel. The crystals are left behind when the wine is drained.

Secondary Fermentation and Bulk aging

The secondary fermentation and bulk aging is a very slow process of fermentation which takes about 3 to 6 months to complete. All this time the wine is kept under fermentation lock (a device which allows carbon dioxide to release while disallows oxygen to enter), to prevent the wine from oxidation. Also the proteins in the grapes are broken down while other particles and the yeast cells settle down. These processes will result in a clear wine which was originally cloudy. The lees can also be removed by racking.

Secondary fermentation is generally done in huge stainless steel vessels or oak barrels. If the winemaker wants oak flavor in the wine, the wine can be fermented in an oak barrel for a brief period or oak chips could be added in a non wooden barrel. But this process is mostly used in cheap wines.

Malolactic Fermentation

The malolactic fermentation process involves the conversion of malic acid into lactic acid by the lactic acid bacteria. The process is carried out intentionally by introducing such bacteria in the maturing wine or it can also happen naturally if the bacteria are already present. Mostly red wines go through this process to reduce the acidity; but sometimes white wine is also fermented in this way to mellow them. The process improves the taste of wine which has got high malic acid, because the acid produces a bitter and harsh taste; while lactic acid is less sour and gentler.

Laboratory tests

When the wine is aging, routine tests are conducted in the laboratory to check the status of wine. The tests conducted on wine are pH, residual sugar, Brix, titrable acidity, volatile acidity, available sulfur and percent alcohol. Some more tests like crystallization of tartar and precipitation of some unstable proteins (only for white wine) are also done. All these tests are performed throughout the winemaking and also before bottling. The winemaker can make required changes in the wine after the results of these tests.

Maturation

The phase of maturation involves the journey of the wine from vine to the bottle. Wine can be matured in either oak barrels or stainless steel tanks. But oak barrels are the most favorable containers for wine maturation. Oak barrels have some advantages over the stainless steel tanks as they bring the very desirable oak flavor into the wine; it also gives protection and allows minute amount  of oxygen to enter the wine which improves the flavor of both white and red wines. American and French oak barrels are most commonly used but as oak barrels can be expensive and need to be changed periodically, many winemakers opt for stainless steel containers instead. Stainless steel tanks are economical as well as easy to maintain. To impart the oak flavor into the wine, some winemakers add oak chips to wines in the steel tanks.

Blending and Fining

Before the wines are bottled, different batches of wines can be blended to acquire the desirable taste. Sometimes wines are also blended to improve the color, flavor or aroma. If there are some inadequacies, the winemaker can rectify them by mixing wines of different grapes and batches which had been cultivated in different conditions. Sometimes it can be as simple as correcting the acid level while at other times it can be complex like blending different vintages or varieties for that desirable perfect taste of wine.

The fining process involves the removal of the unwanted particles in the wine, reducing astringency and removal of tannins. For this process, fining agents are used which can vary for different wine batches or products. The fining agents are mostly animal based like gelatin (which is being used since centuries), egg whites, bull’s blood, bone char, skimmed milk powder etc. or they can be non-animal based agents like cellulose pads, bentonite, paper filters etc.

Preservatives

Sulfur dioxide is the most common preservative used in wines. It is an anti microbial agent and an anti oxidant. In white wines it is added before fermentation and immediately after the alcoholic fermentation. If it is added after the alcoholic fermentation it stops the malolactic fermentation and prevents the damage from oxygen. For red wines, high level of sulfur dioxide is added before the fermentation, to help in stabilizing the color. If sulfur dioxide is not used the wines can be spoilt by bacteria even though every hygiene precaution is taken.

Filtration

Filtration involves clarification and the microbial stabilization of wine. After filtration the wine does not appear cloudy, but clear and bright as expected by the wine lovers. During clarification the bigger particles are removed while in microbial stabilization, the organisms which affect the wine stability are removed.

Bottling

Bottling is the final phase of winemaking. A last dose of sulfite is added in the bottles to preserve the wine and to prevent any undesired fermentation. The bottling of wines is done by the mechanical bottling lines.  The bottles are capped by traditional corks or the modern screw caps depending on the tradition of the winery. A capsule is then added to the top of the bottle and then heated for a tight seal. Finally the bottles are labeled and sent away for aging, storage or distribution.