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The practice of adding spirits, usually grape spirit, containing alcohol to wine to ensure microbiological stability, thereby adding alcoholic strength and precluding any further fermentation.
The principle behind this addition of alcohol is that most bacteria and strains of yeast are rendered impotent, unable to react with sugar or other wine constituents, in solutions containing more than 16 to 18 per cent alcohol, depending on the strain of yeast. The stage at which spirit is added has enormous implications for the style of fortified wine produced. The earlier it is added in the fermentation process, the sweeter the resulting wine will be. Vins de liqueur such as Pineau des Charentes, for example, are simply blends of sweet, hardly fermented grape juice with grape spirit. An even stronger charge of alcohol is added before fermentation to a significant proportion of the rich grape juice used in the production of Australia's Liqueur Muscats and Tokays. For most port style wines (including the sweeter styles of madeira) and for all vins doux naturels, fortification takes place during fermentation. Much of the natural grape sugar is retained by arresting fermentation before its completion, thereby boosting alcoholic strength to a pre-ordained level: usually between 18 and 20 per cent in port but between 15 and 16 per cent in most vins doux naturels. Spirit is added only at the end of fermentation, to dry, fully fermented wine, in the making of sherry, similar wines such as vin jaune, and the drier styles of madeira. Any sweetness in such wines is usually due to a pre-bottling addition of sweetening agent, often itself a mixture of grape juice and spirit (see mistela, PX). The spirit used for fortification comes from a variety of different sources and could be based on grapes, sugar beet, cane sugar, agricultural by-products, or even petroleum. Local regulations specify the types of spirit allowed for a given fortified wine and only grape spirit is allowed for fortified wines of any quality. The spirit used for fortifying port, however, is supplied by the Portuguese monopoly which has, in its time, been unable to provide grape spirit, without any perceptible damage to the final quality of the wines. Carbon dating usefully allows the immediate detection of petroleum-based spirit in any wine, however. The method of distillation of the spirit plays a part possibly even more important than its source. The most neutral spirits are the products of a continuous still which contain a minimum of flavour congeners and tend to be used in the fortification of wines that are designed for early consumption and deliberately exhibit the characteristics of the base wine (the Muscats of southern France, for example). Spirits produced by pot still distillation on the other hand are much more violently flavoured and are rarely added to fortified wines. References alcohol alcoholic strength bacteria congeners continuous still distillation fermentation grape spirit Liqueur Muscat mistela Muscat Pineau des Charentes pot still PX vin jaune yeast
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