Red wine

Red wine is a type of wine made from dark-colored (black) grape varieties. The actual color of the wine can range from intense violet, typical of young wines, through to brick red for mature wines and brown for older red wines. The juice from most purple grapes is greenish-white; the red color comes from anthocyan pigments (also called anthocyanins) present in the skin of the grape; exceptions are the relatively uncommon teinturier varieties, which produce a red colored. Much of the red-wine production process therefore involves extraction of color and flavor components from the grape skin.

The first step in red wine production, after picking, involves physical processing of the grapes. Hand-picked or machine-harvested grapes are usually tipped into a receival bin when they arrive at the winery and conveyed by a screw mechanism to the grape-processing equipment.

On arrival at the winery there is usually a mixture of individual berries, whole bunches (particularly with hand-picked grapes), stems, and leaves. The presence of stems during fermentation can lead to a bitter taste in the wine, and the purpose of destemming is to separate grapes from the stems and leaves. Mechanical de-stemmers usually consist of a rotating cage perforated with grape-sized holes. Within this cage is a concentric axle with arms radiating towards the inner surface of the cage. Grapes pass through the holes in the cage, while stems and leaves are expelled through the open end of the cage.

After destemming, the grapes are commonly lightly crushed. Crushers usually consist of a pair of rollers, and the gap between them can usually be regulated to allow for light, hard or no crushing, according to the winemaker's preference.

The mixture of grapes, skins, juice and seeds is now referred to as must. The must is then pumped to a vessel, often a tank made of stainless steel or concrete, or an oak vat, for fermentation.

In common with most modern winemaking equipment, destemmers and crushers are normally made of stainless steel (food-grade stainless steel for those parts which come into physical contact with the grapes)

The preservative sulfur dioxide is commonly added when grapes arrive at the winery. The addition rate varies from zero, for perfectly healthy grapes, to up to 70 mg/litre, for grapes with a high percentage of rot. The purpose is to prevent oxidation and sometimes to delay the onset of fermentation.

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Wikipedia