Wine is one of the most consumed alcoholic beverages in the world, with a high economic impact. The International Organisation of Vine and Wine reported that in 2018:
292 million hectoliters of wine (including sparkling and special wines) were produced globally;
246 million hectoliters of wine were consumed in the world.
Total wine production (millions of hectoliters) in 2018 in the world. Source: http://www.oiv.int/
WINEMAKING (Food Science)
Winemaking (or vinification) consists in the process of wine production, from the selection of grapes to the bottling of finished wine.
But let’s start from the beginning – wine is an alcoholic beverage produced by the fermentation of the juice of fruits, usually grapes.
The most important phases of winemaking are:
1. Grape crushing and Production of must
During this first stage, the stem is separated from the grapes and discarded, the grape berries are crushed and transferred to the fermentation tank, and the must is produced.
It should be noted that the grape berries have a skin rich of polyphenols (anthocyanins and catechins), aromatic compounds (terpenes), pigments, and tannins. The berry pulp is composed of juice, acids (tartaric, malic and citric), sugars (only glucose and fructose), and small amounts of aromatic compounds and polyphenols.
2. Alcoholic fermentation
After must preparation, selected yeasts, nutrient substances and sulfur dioxide are added.
Yeasts are the microorganisms responsible for the alcoholic fermentation during wine production, converting glucose and fructose existing in the must into cellular energy (ATP), with production of alcohol (ethanol) and carbon dioxide (CO2). Yeasts are generally already present on the grapes and in the winery environment but they can give unpredictable results, hence selected commercial strains of yeast are often added to the must.
Ammonium salts and vitamins (biotin and thiamin) are often added as nutrients for the yeast, as well as sugar if the sugar concentration is low.
Sulfur dioxide is used to: (1) inhibit or kill the natural microorganisms (bacteria and yeasts) in the juice, facilitating the activity of the selected yeasts added to the must; (2) prevent oxidative reactions that would cause change of the juice colour.
For every 100 grams of sugars fermented about 60 mL of ethanol, 24 L of carbon dioxide and 24 Kcal are produced.
During alcoholic fermentation other substances (minor products): glycerol, acetic acid, higher alcohols, and acetaldehyde are also produced. The concentration of these compounds is important to the wine quality. Indeed, a wine with good quality is defined by low concentrations of acetic acid, and higher concentration of alcohols and acetaldehyde.
When the sugar concentration of the must has reached about 10 g/L or less, the must is drawn off the pomace. After pomace and wine separation, the wine is then placed in a storage tank where the alcoholic fermentation runs to completion.
3. Fining, filtration and aging
When the sugar is fully utilized, the malolactic fermentation can take place, where malic acid (associated with the taste of green apples) is converted to lactic acid (associated with a richer and more buttery tasting) by lactic acid bacteria. This process enhances the body and flavor persistence of wine, producing wines of greater palate softness. Finally, the wine is transferred to other tanks for fining (for example, removal of tannic and brown compounds, and elimination of unpleasant odor), filtration and aging.
We did a simple approach, focusing on the main stages of vinification, and it is important to highlight that the production of the white and red wines have some minor differences. To learn more about the science and technology behind winemaking, we recommend reading this article.
References:
Zeppa, Giuseppe (2007). The science and technology of wine making. Available from: https://www.dairyscience.info/index.php/science-and-technology-of-wine/124-the-science-and-technology-of-wine-making.html
Comments