The phenolic content in wine refers to the phenolic compounds—natural phenol and polyphenols—in wine, which include a large group of several hundred chemical compounds that affect the taste, color and mouthfeel of wine. These compounds include phenolic acids, stilbenoids, flavonols, dihydroflavonols, anthocyanins, flavanol monomers (catechins) and flavanol polymers (proanthocyanidins). This large group of natural phenols can be broadly separated into two categories, flavonoids and non-flavonoids. Flavonoids include the anthocyanins and tannins which contribute to the color and mouthfeel of the wine. The non-flavonoids include the stilbenoids such as resveratrol and phenolic acids such as benzoic, caffeic and cinnamic acids.
The natural phenols are not evenly distributed within the fruit. Phenolic acids are largely present in the pulp, anthocyanins and stilbenoids in the skin, and other phenols (catechins, proanthocyanidins and flavonols) in the skin and the seeds. During the growth cycle of the grapevine, sunlight will increase the concentration of phenolics in the grape berries, their development being an important component of canopy management. The proportion of the different phenols in any one wine will therefore vary according to the type of vinification. Red wine will be richer in phenols abundant in the skin and seeds, such as anthocyanin, proanthocyanidins and flavonols, whereas the phenols in white wine will essentially originate from the pulp, and these will be the phenolic acids together with lower amounts of catechins and stilbenes. Red wines will also have the phenols found in white wines.
Wine simple phenols are further transformed during wine aging into complex molecules formed notably by the condensation of proanthocyanidins and anthocyanins, which explains the modification in the color. Anthocyanins react with catechins, proanthocyanidins and other wine components during wine aging to form new polymeric pigments resulting in a modification of the wine color and a lower astringency.
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Maceration is the winemaking process where the phenolic materials of the grape—tannins, coloring agents (anthocyanins) and flavor compounds—are leached from the grape skins, seeds and stems into the must. To macerate is to soften by soaking, and maceration is the process by which the red wine receives its red color, since raw grape juice (with the exceptions of teinturiers) is clear-grayish in color. In the production of white wines, maceration is either avoided or allowed only in very limited manner in the form of a short amount of skin contact with the juice prior to pressing.
The annual growth cycle of grapevines is the process that takes place in the vineyard each year, beginning with bud break in the spring and culminating in leaf fall in autumn followed by winter dormancy. From a winemaking perspective, each step in the process plays a vital role in the development of grapes with ideal characteristics for making wine.
The acids in wine are an important component in both winemaking and the finished product of wine. They are present in both grapes and wine, having direct influences on the color, balance and taste of the wine as well as the growth and vitality of yeast during fermentation and protecting the wine from bacteria. The measure of the amount of acidity in wine is known as the “titratable acidity” or “total acidity”, which refers to the test that yields the total of all acids present, while strength of acidity is measured according to pH, with most wines having a pH between 2.
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