Wine processing

We all are very familiar with the term wine. Wine is a very common alcoholic beverage which can be made by partial or complete fermentation of ripe grape juice or concentrate. Other berries, apples, oranges, juice of palm tree, pears can also be used as a raw material for making wine. Mostly grapes are used for wine making.

Based on sugar content there are two types Dry wine (very little or no sugar) and Sweet wine (high sugar). Alcohol content in wine generally varies form 7-21% based on different varieties and their requirement.

Wine making is very unique and interesting topic to write upon it. Process involves various steps such as harvesting, crushing & pressing, fermentation, clarification and bottling which are followed by aging & maturation whose time varies from variety to variety.

HARVESTING

The primary step for manufacturing of any product depending on raw-materials directly obtained from agricultural practices. Fully ripened and sound grapes are used for wine making. Selection of species of grapes for particular variety of wine is essential. Grapes with black skin is preferred for making red wine while black or white both varieties can be preferred for white wine after removing their skin.

 
CRUSHING AND PRESSING

After selecting the suitable fruit, crushing is the second operation in wine making. Grapes are crushed and stemmed in a crusher-stemmer which consists of a perforated cylinder containing paddles revolving at 600-1200 revolutions per minute. Roller crusher can also be used for the crushing operation.

After the crushing the crushed mass of grapes are pressed using basket press to extract the juice. Continuous screw type press can also be used.

 
ADDITION OF SUGAR AND PRESERVATIVES

Cane sugar is usually added to maintain the TSS of the wine. TSS of the wine should be maintained between 20-24%. When the grapes used for wine making tastes sour, the cane sugar is added 70grams per kilogram of grapes.
Small amount of KMS is also added to inhibit the growth of any wild yeast or other spoilage organism. After 1-2 hours of adding KMS, wine yeast is added at the rate of 10ml per 5kg of grapes. Saccharomyces Ellipsoideus inoculum is added into the juice.

FERMENTATION

The most important step in wine making. Converts the sugar into the alcohol to raise the alcohol level in the juice. This process of alcoholic fermentation requires careful temperature control. The fermentation vessel must be closed. The number of fermenting yeast should be adequate with proper nutrition. This process is generally kept for 2-3 days at 22-280C temperature based on requirement.

CLARIFICATION

After the fermentation step wine becomes turbid due to presence of dead cell of yeast and some other impurities. So, this step is very essential to increase the visual appeal of the wine. The whole content is passed through a thin muslin cloth or a filter aid to remove maximum of the impurities. Fining is done with the filtrate produced after filtration to remove the remaining impurities. Bentonite, a fining agent is added. All the colloidal particles settle down along with bentonite and the clear wine is syphoned off from the top and the process is known as racking.

AGING/MATURATION

Quality of the wine improves during the time of barrel or bottle storage. Acidity of the wine decreases with the time. Aging process also gives the advantage of additional clarification as the undesirable substances settle down at the bottom.  which affects its flavor and aroma. Wooden barrel made up of oak is generally used for storing. Generally wines are allowed to mature for 6 to 8 months or more depending on the variety and the demand of flavor and aroma in wine.

BOTTLING

Wine may require the use of antiseptics, blending and filtration before bottling to prevent the development of various microbes. Acid content of the wine should be low before bottling. Mainly volatile acid, acetic acid is present in the wine which may support the growth of acetic acid bacteria which can cause the spoilage. Pasteurization of wine is done before bottling at 82-88 0C for 1-2 minutes to destroy the growth of spoilage organism. After pasteurization wine is filled into the bottles and gets sealed with the help of crown cork of good quality. In-bottle pasteurization can also be done to decrease the chance of growth of microbes and increasing it shelf life. In-bottle pasteurization is carried out at temperature 65 0C for 20 minutes.