During the fermentation process, the natural sugars of the grape juice are converted to alcohol and carbon dioxide is released through the action of yeasts. Wines are preferably fermented in stainless steel tanks, as they are inert, easy to clean, and facilitate control of the fermentation temperature. The ideal temperature to ferment wines is usually around 55o F because cool temperatures best extract their fresh, fruity qualities. Fermentation of reserve wine in French oak barrels occurs at higher temperatures, which allows air to reach the wine, imparting phenolic and flavour extracts from the barrel, thus enhancing the richness and complexity of the wine.
The aging process allows the aromas and flavours of the wine to develop and be well-defined before bottling. Aging in stainless steel tends to preserve wine’s fresh, fruity characteristics, while aging in French oak barrel develops distinct secondary characteristics due to delayed oxidation and the extraction of barrel tannins, aromas and flavours.
Clarification can be accomplished by several techniques like:
Racking - removing the wine using gravity by separating the sediment that settles at the bottom of an aging vessel and transferring it to another container.
Filtration - passing the wine through a filter medium like a pad, or membrane filter to remove suspended particles.
Filtration is used to remove unwanted microorganisms that affect the stability of the wine and reduce the likelihood of re-fermentation or spoilage. But it also minimizes the tannin levels, and can strip aroma and flavour from a wine, so normally winemakers opt for racking, when possible, or minimum filtration, when required.
There is a famous saying among fine wine producers that ‘great wines are made in the vineyard.’ While it is possible to make bad wine from good grapes, it is practically impossible to make exceptional wine from sub-standard grapes. The most important factors that result in quality grapes are summarized below:
The best wines come from locations whose temperate climates facilitate a long growing season of the grapes. Grapes grown on well-drained, less fertile, hillside soils often possess better character than those cultivated in more fertile, valley-floor soils. Grape varieties should be cultivated in micro-climates in order to maximize their potential – e.g., chardonnay grows well in cooler climates, whereas cabernet sauvignon flourishes in warmer regions.
The main objective of canopy management is to strike a balance between the vine’s vegetative growth and its fruit development. Grape growers remove shoots and leaves during the growing season to ensure adequate air flow through the vine and the grape clusters are exposed to both direct and indirect sunlight. They may also trim clusters for a simple, yet economically feasible, crop of fully ripened grapes.
To produce fine wine, great care is taken so that the grapes arrive at the winery in perfect condition. The grapes are hand harvesting at cool temperatures in the night or early morning to retain the physiological integrity of the grapes.
Summarized below are the standard steps in the vinification process for grape wines:
Crush & destem
After the grapes make it to the winery, they are mechanically crushed and de-stemmed. This process releases some free run juice, and segregates the fruit from the stems, to avoid the possibilities of imparting bitter tannins to the juice. The grapes are then subjected to tank presses, which extract the juice from the skins and reduce the tannins released from skins and seeds. Overall, this process minimizes the bitter phenolic contents in the wine.
After crushing and destemming the grapes, the unfermented juice along with skins and seeds are immediately pressed, in pneumatic bladder press, to separate the juice from the skins. The degree of the press affects the quality of the resulting wine. Therefore gentle pressure is preferred to extract the juice from the skins.