Discover the marvels behind how wine is brewed and the micro-organisms involved.
People love wine. They drink them for many reasons - for its taste, to get energetic, for good health and even just for fun. Ranging from fortified wines to sparkling wines, they are all marvelously made from the finest grapes you can find around the world. However, many fail to discover the marvels behind how wine's made. Micro-organisms play a crucial role in wine making, and it's important to know how they do the job. Below, you may learn the steps on how wine is processed.
The Micro-Organisms Involved
Yeasts
They are unicellular, eukaryotic micro-organisms classified under fungi
Most of them reproduce asexually by budding (others by binary fission eg. Schizosaccharomyces)
They usually measure at about 4 µm
They are heterotrophs which do not make their own food but instead act as parasites which will obtain food and seek shelter from host organism
They are characterized by a wide range of natural habitats, and are usually found in soil, plants or skin surfaces in mammals.
The species Saccharomyces are used for baking or fermenting alcoholic beverages like beer and wine.
The species Candida albicans are pathogens that can infect humans and can cause diseases or infections such as diaper rash or trush in the mouth.
Bacteria
They are rod-shaped, unicellular, eukaryotic micro-organisms classified under fungi
They reproduce asexually by binary fission (division)
They are heterotrophs which do not make their own food but instead obtain food by acting as saprophytes, decomposing organic substances or as parasites, feeds on and seek shelter from host organisms.
The species Oenococcus oeni (lactic acid bacteria) plays an important role in de-acidifying wine during the process of wine making.
We shall now find out the 6 steps to wine making. Each step has its own reason behind it.
Harvesting
Grapes are the key ingredient for making good wine. They, and not other fruits, are used because of the sufficient amount of sugar in them to yield enough alcohol during the process of fermentation. The presence of acids, esters and tannins for making stable wine constantly also make grapes a good choice. Either by mechanism or by hand, the fruit will be harvested and be brought from the vineyard to the winery where winemakers sort out the ripe grapes from the unripe or rotten ones to be made into wine.
Crushing & Pressing
The carefully selected grapes are then passed through a machine called de-stemmer/crusher that separates the fruit from the stem and crushes it to release the juice. The product, known as must, will be transferred to a tank for the fermentation process. As for making white wine, the must will be pressed to remove the skin and seeds. The amount of pressure applied will affect what flavour compounds are extracted from the skin.
Fermentation
This is the crucial step for grape extracts to turn into alcohol. There are two steps to fermentation - alcoholic fermentation and malolactic fermentation. During alcoholic fermentation, wine is stored in wooden or steel containers, and wild yeast will start to form under warm temperatures. However, in order to achieve desired characters of the wine, the process of inoculation is introduced with the help of cultivated yeast. The two yeast species, Saccharomyces cerevisiae or Saccharomyces bayanus, are used to convert the sugars in the must into ethanol. Depending on the type of wine that will be produced, the duration of fermentation varies for a few days to a few weeks. For instance, lighter red wines will be left to ferment for 2-3 days while full-bodied red wines will spend more than 2 weeks fermenting. For the second step, bacteria that grow in the tanks will reduce the acidity of the wine by converting malic acid into lactic acid, thus making the wine less sour. However, they can also play a part in spoilage the flavour of the wine it is in.
Aging
At this stage, winemakers can choose to age the wine or not depending on what wine they are producing. Wines that are to undergo the process of ageing will be stored containers or barrels to allow the wine to mellow out. The duration of ageing, the type of container used and the temperature of which the wine is stored at all influences the flavour and character of the wine. Red, fortified wines will spend a long period of time of about 2-10 years in their containers to allow more influence to the tannin contents. As for white wines, they need little or no ageing period, and tannin in the wine is influenced the least.
Clarification
After mellowing the wine, course particles and unwanted sediments will settle at the bottom of the tanks, and they will be trapped when the wine is siphoned or filtered from one tank to another. Then, there will be fining where compounds such as clay will be added to precipitate dead yeast cells away from the wine. After that, the clarified wine will be ready to be bottled.
Bottling
The final product will be classified by winemakers into different groups, mainly table wines, sparkling wines, and fortified wines, and will then be pasteurized before being sent to bottling lines where they are bottled and transported away to fulfill the demands of consumers.
It's a Fact
Wine attracts not only yeasts, but also harmful bacteria and molds which will spoil the wine. A common bacterium Acetobacte, if present in wine, will convert alcohol into acetic acid (vinegar). Thus, winemakers will add sulphur dioxide to prevent growth of bacteria, molds and wild yeast, and at the same time inhibit oxidation of wines.
The Fermentation Process
Yeasts are the ones responsible for alcoholic fermentation. They, being an anaerobic micro-organism, will convert sugars (carbohydrates) into ethanol and carbon dioxide under conditions where there is no oxygen. Some of the enzymes present in the yeast will catalyse the breakdown of starch into glucose, while other enzymes will catalyse the breakdown of sugar molecules (made up of carbon, hydrogen and oxygen atoms) into ethyl alcohol (ethanol) and carbon dioxide. These products provide energy for the yeast's various metabolic activities such as growth and reproduction by budding. Carbon dioxide that is produced can be trapped and used to make sparkling wines.
Lactic acid bacteria are responsible for lacolactic fermentation. The bacteria will grow in the wine and will convert the unpleasant malic acid in the wine into more favourable lactic acid and carbon dioxide. This decarboxylation reaction educes the acidity of the wine. Lactic acid bacteria also influence and modify the flavour of the wine and add some flavour compounds from their metabolic activities.
