Dave McIntyre has written a very nice article (“How to Put Riesling Fears to Rest”) on Riesling in the Washington Post of January 7, 2009. Riesling is a rising star in the wine world and the International Wine Review plans to devote a report to the Riesling renaissance in one of its coming issues. Dave McIntyre discusses the problem that the taste of a Riesling wine can range from bone-dry to exceptionally sweet and thus consumers are often a bit lost when they see a Riesling in the shelf of a wine store. The purpose of this posting is to shed some light on why some Rieslings are sweet and others dry, with special reference to German wines.
To start, some basics, which are often not well understood, but which are fundamental to the issue: The fermentation of grape must is a complex process in which sugars, naturally present in grape juice, are transformed into alcohol and carbon dioxide by the action of yeasts. The fermentation process stops when the alcohol level in the wine has reached around 13 to 15 percent of the volume. In most cases, all the sugar in the grape is fermented by then and the wine is dry. Thus, all over the world, even in the warmer regions, wine tends to be dry. The main role of sugar in the grapes is to produce alcohol in the wine. At the end of the fermentation, the sugar is gone, converted into alcohol.
But there are exceptions. Germany is one of the countries that is well known for sweet dessert wines. These fine sweet wines are produced either from botrytised grapes or grapes that were harvested during frost, more specifically,
• the fog in the autumn mornings at German river banks produces a fungal infection, botrytis cineria (noble rot), which removes the water in the grapes and adds a unique flavor to the grape; and
• the frost late in the year also removes the water (but does not produce the botrytis taste).
In both cases, the sugar content of the grape is exceptionally high at the time of the harvest and mother nature is unable to ferment all the sugar. Thus, natural sugar remains in the wine and makes the wine sweet. These are the famous sweet dessert wines in Germany: Beerenauslese, Trockenbeerenauslese, Eiswein.
But Germany is also known for producing sweet non-dessert wines, ranging from simple and cheap party wines to rich and delicate sweet Spaetlese and Auslese wines. What makes these wines sweet is not the sugar content in the grapes, but the skillful processing of the must by the winemaker in the cellar. Germany’s Spaetlese and Auslese wines, as well as lower quality wines, have a sugar content in the grapes at harvest that normally is fully fermented, even Spaetlese and Auslese wines. Yet, they are often sweet.
There are two principal methods used by German winemakers to generate residual sugar in such wine: First, stopping the fermentation (skillful manipulation of the fermentation process with sulfur and temperature control, among others, which arrests the fermentation and keeps the sugar level high in the wine) or adding what is called suessreserve (unfermented grape juice) after completion of the fermentation to the dry wine. Thus, any German wine ranging from Tafelwein to Spaetlese/Auslese is dry, unless the winemaker decides otherwise. If he does so, he can either arrest the fermentation or add suessreserve. A good indication if a sweet Spaetlese was stopped or not is the level of alcohol. If it is low, the likelyhood is large that the wine was made sweet by arresting the fermentation. In recent years, adding suessreserve has become the preferred method.
German wine makers can also add sugar to the grape must. And they do. But this does not make the wine sweet. Winemakers are constrained by the law in terms of the quantity of sugar they can add and in terms of sugar content of the grapes. Only grape juice from grapes with a low sugar content can be enriched within certain limits with the purpose to bring the alcohol level to desired level. Again, these wines are typically dry, notwithstanding the sugar, if the winemaker does not manipulate the fermentation, but can be made sweet if the winemaker stopps the fermentation or adds suessreserve after fermentation..
I love the whole range of German white wines, in particular Rieslings, depending on the occasion. For foie gras, I get a ultra-sweet Riesling Trockenbeerenauslese; I like my veal breast with cream sauce and a bone-dry Auslese from Rheingau and Chinese Food with a sweet Auslese: and I serve a light, spritzy, off-dry Mosel Qualitaetswein at my summer parties.