Wine production using fruit juice
Wine is an alcoholic beverage, made of fermented fruit juice, usually from grapes. The natural chemical balance of grapes lets them ferment without the addition of sugars, acids, enzymes, or other nutrients. Grape wine is produced by fermenting crushed grapes using various types of yeast. Yeast consumes the sugars in the grapes and converts them into alcohol. Different varieties of grapes and strains of yeasts produce different types of wine. Wines made from other fruits, such as apples and berries, are normally named after the fruit from which they are produced (for example, apple wine orelderberry wine) and are generically called fruit wine or country wine. During fermentation, yeast interacts with sugars in the juice to create ethanol, commonly known as ethyl alcohol, and carbon dioxide (as a by-product). In winemaking, the temperature and speed of fermentation are important considerations as well as the levels of oxygen present in the must at the start of the fermentation. In winemaking, there are different processes that fall under the title of “Fermentation” but might not follow the same procedure commonly associated with wine fermentation.
Grape wine is perhaps the most common fruit juice alcohol. Because of the commercialisation of the product for industry, the process is well known and documented.
The production of grape wine is quite straight forward and can be carried out at the small-scale, without the need for very expensive or specialised equipment. It does, however, require a basic understanding of the processes involved, tightly controlled fermentation conditions to ensure a high quality product and a strict adherence to cleanliness and hygiene to prevent contamination of the wine by spoilage bacteria.
Essentially, wine production involves the following basic steps;
- crushing the grapes to extract the juice
- alcoholic fermentation
- bulk storage and maturation of the wine in a cellar
- clarification and packaging.
There are really two distinctive types of wine made from grapes – red wine and white wine. The main difference in the two types is the variety of grape used as raw material and the removal of grape skins in the production of white wine. Grapes contain a number of chemical compounds that all contribute to the flavour and colour of wine. Tannins are one group of compounds that give the wine a bitterness and astringency. The tannins are found in the grape skins, therefore red wines tend to be more astringent than white wines.
Principles of winemaking
Wine making uses the following basic principles:
- The sugars present in the fruit (and any sugar that is added to the fruit) are fermented by yeast that is added to the mixture. There are natural yeasts present on the skins of fruits, but these are usually not sufficient to carry out the fermentation on their own.
- When sugar is fermented by yeast, it is converted into alcohol (ethanol) and carbon dioxide gas is released.
- The fermentation has to take place without oxygen (it is an anaerobic fermentation). If oxygen gets into the system during the fermentation, the alcohol will be converted into acid (this is what happens when you make vinegar, which is acetic acid). Wine that has spoiled because it has been exposed to the air may taste very acidic.
- There are lots of bacteria and yeasts around in the air and on the surface of the fruits. They all have the potential to spoil the wine. It is extremely important that these bacteria do not start to grow in the fermenting grape juice. Particular care must be taken with the cleanliness of the equipment and personal hygiene.
- All equipment must be sterilized with a solution of sodium or potassium metabisulphite before it is used