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Wine Glossary: XYZ

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Yeast
A micro-organism without which we would not have bread, beer or wine - wouldn't life be dull! The yeasts convert the sugar to alcohol in a process known as alcoholic fermentation. Present naturally in the vineyard, harvested grapes will begin to ferment naturally, especially if they are crushed to break the skins and expose the sugar-rich juice inside to the yeasts which reside on the grape skins. Some winemakers prefer to add cultured yeasts rather than rely on the action of wild yeasts. This gives greater control over the fermentation, but some argue it may intrinsically alter the style or quality of the wine, as a single strain might not produce the same flavours as the multiple strains present in the vineyard.

Yield
The yield is the amount of wine produced in vineyard or estate, and is usually expressed in hectolitres per hectare in much of Europe, or in tons per acre in much of the New World. Conversion between the two is difficult as the European system is based on volume of wine produced, whereas that found in the New World is based on the mass of the harvested grapes. Mass of grapes and volume of wine are clearly related, but the relationship varies according to grape variety and colour, and winemaking practises. A very rough rule of thumb is that 1 ton/acre is equivalent to 15 hl/ha for white wine and 20 hl/ha for red wine. Yields vary according to the type of vine - some are heavy croppers, some yield less - and also with climate and soil. Yields may be influenced by the winemaker, who may perform a green harvest on order to reduce them. Low yields are associated with increased quality.

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