Sweet Winemaking

sweet winemaking, the production of wines with noticeable amounts of residual sugar which may vary considerably in alcoholic strength and production techniques. Local regulations differ significantly but, with a few exceptions, non-grape sugar may be added only (and rarely) for the purposes of chaptalization, to increase the final alcoholic strength, and not to add sweetness after fermentation. The most common method of sweetening basic wine is the addition of some form of sweet grape juice, followed by stabilization (for any wine containing sugar is theoretically susceptible to a second fermentation).

The finest sweet wines are made by concentrating the sugar in grapes, however, and the combined effect of the alcohol produced and the residual sugar tends to inhibit further yeast activity. The four common ways of doing this are by the benevolent noble rot effect of the botrytis fungus on the vine as it nears maturity in perfect conditions (see botrytized wines); by processing frozen grape clusters (see eiswein and cryoextraction); or by drying mature grapes either on the vine or after picking (see dried-grape wines). Many sweet wines are made by simply leaving the grapes on the vine for as long as possible in order to concentrate the grape sugars. (see late harvest). If botrytis bunch rot fails to materialize, the grapes simply start to raisin or shrivel, a condition known in French as passerillage. Such wines, sweet jurançon, for example, described as moelleux in French, can be extremely rich and satisfying, but are typically less complex and less long-lived wines than those made from grapes transformed by the action of noble rot.

Some everyday sweet wines are made simply by fermenting the wine out to dryness and subsequently adding sweet reserve, grape concentrate, or rectified grape must just before a sterilizing membrane filtration and sterile bottling. These wines owe their stability not to their composition but to the fact that all micro-organisms have been filtered out. They are best drunk within a year of bottling and within a day or two of opening the bottle. liebfraumilch is an example of this type of wine, and the sweetening agent is called süssreserve in German.

Another technique, commonly employed for inexpensive sweet white French wines, is to ferment a must relatively high in sugars, between 200 and 250 g/l, until the alcohol level has reached about 11 or 12%, and then add a substantial dose of sulfur dioxide.

One quite different way of transforming grapes into a liquid that is both sweet and stable is to add spirit to grape juice either before fermentation (see mistela) or during it (see vin doux naturel). Such liquids are usually more than 15% alcohol, much stronger than most table wines.

Many fortified wines are sweet. See also late harvest, botrytized wines, dried-grape wines, and eiswein for details of how these particularly fine sweet wines are made.