GENERAL METHODS FOR FRUIT WINEMAKING

 

GENERAL METHODS FOR FRUIT WINEMAKING

Preparation of Yeast Starter Culture

            A good strain of the wine yeast S. cerevisiae is a prerequisite and needs to be procured for making quality wine. The yeast in the form of slants, tablets, or compressed yeast can be used for this purpose. Before the same is added to the must for fermentation, the yeast culture is activated in the juice/pulp intended for winemaking. The container with the juice is plugged and kept in a warm place (25–30°C) and the culture is ready after 24 h. The amount of active culture is added at 2–5% to the must. The yeast, when used in the tablet form, is activated in sterilized water at the optimum temperature for yeast growth. However, compressed yeast can be added directly to the must.

 

Preparation of Must

            The juice or the pulp of the fruit to be used for winemaking is made into must. The must is prepared depending on the fruit used and the type of wine to be made. Either the juice is extracted or the fruit is made into pulp. Juice from fruits like apple is extracted first by grating, followed by pressing in a hydraulic press. Usually, pectinol is added to the must to help clarify the wine, as its addition has been found to enhance the quality of wine. SO2 is added to the must at 100–150 ppm as potassium metabisulfite. The addition of ammonium sulfate with thiamin and biotin gives a greater increase in the rate of fermentation. In apple juice, ammonium sulfate with 4 mg/L thiamine gives a much greater effect on the fermentation rate. Fining with gelatin has been found to be a good remedy for juices like pear, which have high tannin contents. Further, heating of the juice for 35 min at 122°F can also increase the fermentation rate. In the case of fruits like plum or peach, an appropriate dilution is made and then, amelioration is done.

Fermentation

            The must is allowed to ferment at a suitable temperature (20–25°C) after inoculation with the yeast culture. A temperature higher than 25°C should be avoided as it causes the loss of volatile compounds and alcohol. The container in which fermentation is carried out has to be equipped with an air lock . The sugar content or °Brix is measured regularly to monitor the progress of fermentation. Normally, the fermentation is allowed to proceed until all the sugar is consumed completely (usually Brix reading of about 8°B). When the fermentation is completed, the bubbling due to the production of CO2 is stopped. At the industrial scale, fermentation is carried out in fermenters of various shapes and sizes.

Siphoning/Racking

            After the completion of fermentation, the yeast and other materials that settle at the bottom of the container, with the clear liquid separating out, is siphoned/racked or, in the case of pulpy must, it is filtered through a cheese/muslin cloth, followed by siphoning. At the industrial scale, a filter press is used. Two or three rackings are usually done after 15–20 days. During the interracking period, no headspace is kept in the bottle or  container, which is closed tightly to prevent any acetification. With the help of a vacuum pump, racking can also be practiced in industrial fermentation with an advantage over not doing racking.

Maturation

            The fresh wine is harsh in taste and has a yeasty flavor. The process of maturation makes the wine mellow in taste and fruity in flavor in addition to the clarification. The period may extend from 6 months to 2–3 years. The process of maturation is complex and the formation of esters takes place thus, improving the flavor of such beverages

 

Clarification

            If the wine is not clear after racking and maturation, it is clarified using filtering aids such as bentonite or celite or by tannin/gelatin treatment followed by filtration in a filter press (Plate 1.2D). These treatments usually make the wine crystal clear.

 

Pasteurization

            Wines, being low-alcohol beverages, are pasteurized at 62°C for 15–20 min, after keeping some headspace in the bottle and crown corking the same. Heating the wines helps the precipitation of tannins or other such materials that are heat sensitive in addition to the preservation. Pasteurized wines however once opened have to be kept at low temperature to prevent their spoilage. Alternatively, table wines can be preserved by the addition of preservatives like SO2, sodium benzoate, sorbic acid, etc.