Monday, August 24, 2009
German Wine Basics: How does a sweet German Riesling become sweet?
There is a large variety of different types of German Rieslings. They can be dry or sweet and those that are sweet can be sweet for different reasons, reflecting factors before harvesting (the land) or reflecting factors during fermentation in the cellar (the hand). The purpose of this blog is to shed some light on these various factors.
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,
First, 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
Second, the frost late in the year, which also removes the water in the grapes when the temperatures fall (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 (the land), but the skillful processing of the must by the winemaker in the cellar (the hand). 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 methods used by German winemakers to generate residual sugar in such wine:
First, stopping the fermentation; this is typically done through a skillful manipulation of the fermentation process with sulfur and temperature control. The winemaker needs to follow closely the fermenation process and must make sure that it comes to a stop at the desired level of sugar.
Port wine, which is always sweet, is also made by stopping the fermentation process. But in the case of Port wine, what stops the fermentation process, is the adding of alcohol to the must and both the alcohol and sugar level in the finished wine become high.
Second, the other technique is to let the wine first fully ferment and then add to the dry and fully fermented wine sterilized grape juice (called in German "Suessreserve"). Here the winemakers lets the wine fully ferment to produce a dry wine and then experiments with different amounts of Suessreserve to achieve the desired level of sweetness in the final product. Ideally, the Suessreserve comes from the same wine. It needs to be sterilized so it does not begin to ferment after it is added to the wine.
Thus, any German wine ranging from Tafelwein to Spaetlese/Auslese is dry, unless the winemaker decides otherwise. If he or she does so, he or she 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 likelihood 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. This is called chaptalization in neighboring France and widespread there for the whole range of wines. But capitalization does not make the wine sweet. The purpose is to increase the alcohol level in the wine, not the sugar level.
Winemakers in Germany 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. Thus, at the Kabinett, Spaetlese, Auslese, Beerenauslese, Trockenbeerenauslese and Eiswein levels, wines are not allowed to be chaptalized. But winemakers at times feel that chaptalisation would benefit a wines at the Kabinett or Spaetlese and they do it, but then have to declassify their wine.
Again, those wines that are chaptalized tend to be dry, notwithstanding the sugar that was added; but it can be made sweet if the winemaker stops 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.
This is a revised version of my earlier posting on the i-winereview blog