Wine Analysis

Abstract

Wine is an alcoholic beverage which results from the fermentation of sugar-containing plant fruit. More strictly speaking, wine is the product of enzymic transformation of the juice of the berries of grape into a beverage containing alcohol. Originally, the fermentation was brought about by the natural yeasts attached to the surface of the ripe harvested berries. The activity of yeast cells on the sugars of the grape juice results in the production of alcohols, carbon dioxide, heat and many other secondary plant products in small quantities. A secondary or malolactic fermentation often takes place, particularly in red wines, whereby lactic acid bacteria convert malic acid into lactic acid. Natural yeast found on the skin of the berries comes in many different strains and ecotypes, each of which will produce a different assortment of by-products during the fermentation reactions, characteristic for the particular types of wine. Saccharomyces cerevisiae is the main species of yeast important in wine-making, although many other yeasts may be present at the start of fermentation. As fermentation proceeds, these other yeast species are strongly inhibited. Modern wine-makers prefer to introduce specially cultivated yeast strains, which help to guarantee the product they are aiming for. These yeast strains may have been selected for certain desirable characteristics such as resistance to high sugar concentrations or to sulfur dioxide. The sulfur dioxide is often added to prevent undesirable bacterial fermentation of the grape juice.