Five major steps are involved in commercial production of wines. They are :
(a) Crushing. Grapes are harvested and ripened to a stage they contain highest sugar percentage. These fruits are crushed in a wine press and the crushed fruits with juice are called "must". The must is generally treated with SO2 to prevent microbial spoilage.
(b) Fermenting. The "must" is now inoculated with the starter culture of selected strain of the yeast and is aerated slightly to promote vigorous yeast growth. Once the fermentation starts, the rapid production of CO2 maintains anaerobic condition. The temperature is kept usually at 25-30°C during fermentation period ranging from 5-11 days in order to inhibit multiplication of wild yeast and undesirable bacteria that live high temperature.
When most of the sugar is fermented the juice is separated from solid parts of fruits by allowing it to pass into tanks. These tanks, provided with valves to let the CO2 escape, are completely filled with juice. The anaerobic condition for alcoholic fermentation is allowed to continue for about 12 days to increase the percentage of alcoholic concentration.
The wine is then allowed to mature in wooden tanks for 2 to 5 or more years. During maturing period the wine clears and develops the desired flavour of volatile ester.
The wine may be finally cleared with the addition of gelation, casein or Spanish clay. The cleared wine is filtered, bottled and pasteurized to prevent microbial spoilage.