Wednesday, January 27, 2010

German Wine Basics: Sugar in the Grape - Alcohol and Sweetness in the Wine

Picture: Christian G.E. Schiller and Betram Verch in the Red Slope in Nierstein, Germany

The sugar content of the fruit at the point of harvest is at the heart of the German wine classification system. The higher the sugar content in the grapes at the point of harvest, the higher the classification of the wine.

There are different approaches for measuring the sugar content, like Celsius and Fahrenheit for the temperature - America uses Fahrenheit, Europe uses Celsius. For the sugar content in the grapes, Americans use the Brix scale, Germans use the Oechsle scale.

Based on the Oechsle scale, German wine is classified into nine quality groups, ranging from Tafelwein with the minimum Oechsle degree of 44 to Trockenebeerenauslese with a minimum Oechsle degree of 150. The minimum Oechsle degrees differ somewhat between Germany’s wine regions and between red and white wine. The numbers indicated below are those for the white wines from the Mosel valley.

Tafelwein (Table wine) - the lowest German quality class; has to have at least 44 degrees of Oechsle in the vineyard.

Landwein (Country wine) - 47 degrees of Oechsle at the minimum.

Qualitaetswein bestimmter Anbaugebiete (QbA wine) means a quality wine from one of the thirteen specified German wine regions; close to half of German wine is QbA wine - 50 degrees Ochsle.

Kabinett - 67 degrees Oechsle.

Spaetlese means late harvest but this are simple wines made from grapes with a higher level of Oechsle - 76 degrees, not necessarily wine made with grapes harvested late in the season.

Auslese - 83 degrees of Oechsle.

Beerenauslese - 110 degrees of Oechsle.

Eiswein - icewine, the same minimu level of 110 degrees of Oechsle.

Trockenbeerenauslese - 150 degrees of Oechsle.

To be clear: the Oechsle degrees measure the sweetness of the grapes at the point of harvest. But this has nothing to do with the sweetness of the finished wine. Same 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. During fermentation, the sugar content of the must declines, while the alcohol content increases and the CO2 disappears. Another by-product is heat. This process stops automatically when the alcohol level in the wine has reached around 13 to 15 percent of the volume. If just left to mother nature, such a wine would have a normal alcohol content and would be a dry, like most of the wines in the world.

More specifically, during the process of fermentation, enzymes break down the sucrose molecules into glucose and fructose, which can then be fermented by the yeast and converted into alcohol and carbon dioxide. In addition to contributing to the body of the wine, higher alcohol levels also bring out the intensity of the fruit.

Picture: Old Cask Cellar C. von Schubert, Mosel

There is a straightforward link between the sugar content in the fruit and the resulting alcohol level in the wine. Look at the table below. For a wine with 13.0 percent alcohol, for example, one needs grapes at the 90 degrees Oechsle level. This would be a bone dry wine. 90 degrees Oechsle is well beyond the Spaetlese category and high up in the Auslese category. Thus, all of Germany’s Spaetlese wines and most Auslese wines, if left to mother nature only, should be dry. You have to go beyond that - say 110 degrees Oechsle - for the fermentation to stop naturally and sugar to remain in the wine.

40 Oechsle ===> 5.3% Alcohol
44 Oechsle = Minimum Tafelwein
47 Oechsle = Minimum Landwein
50 Oechsle = Minimum QbA ===> 6.9% Alcohol
60 Oechsle = 14.7 Brix ===> 8.4% Alcohol
67 Oechsle = Minimum Kabinett
70 Oechsle = 17.0 Brix ===> 9.9% Alcohol
76 Oechsle = Minimum Spaetlese
80 Oechsle = 18.1 Brix ===> 11.4% Alcohol
83 Oechsle = Minimum Auslese
90 Oechsle = 21.5 Brix ===> 13.0% Alcohol
100 Oechsle = 23.7 Brix ===> 14.5% Alcohol
110 Oechsle = Minimum Beerenauslese ===> 15.9% Alcohol
110 Oechsle = Minimum Eiswein ===> 15.9% Alcohol
120 Oechsle ===> 17.4% Alcohol
150 Oechsle = Minimum Trockenbeerenauslese

More general, all German wines up to the Auslese category are potentially bone-dry. Once we move above to the Auslese to Beerenauslese, Trockenbeerenauslese and Eiswein, the fermentation stops naturally and sugar remains in the wine. This are Germany’s flagship noble-sweet wines.

Three issues arise.

First, in reality you have sweet German wines that are below Auslese level.

In fact there is plenty of such wines. How do winemakers do this? 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 fermentation process and must make sure that it comes to a stop at the desired level of sweetness.

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.

Picture: Hochheim/Rheingau

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.

Second, the noble sweet wines.

Noble sweet wines, however, is a different story. The fruit has such a high sugar level at harvest that there is nothing you can do preventing the wine to remain sweet. These noble-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.

Third, chaptalization is legal and normal.

Chaptalization is legal and normal, but only for wines in the Tafelwein, Landwein and QbA categories, which accounts for about 60% of German wine. From Kabinett wines upwards, chaptalization is not allowed. It is obvious that chaptalization is not a means of increasing the sweetness of the wine but of the alcohol content, as in neighboring France.

For Deutscher Landwein, for example, the fruit must have at least 47 degrees of Oechle in the Mosel valley. To reach a sufficient alcohol content, the must needs to be chaptalized. Its sole purpose is to increase the final alcoholic strength of a wine - the added sugar (along with the grapes' natural sugar) is converted during fermentation. The EU wine law limits the amount of additional alcohol that can be achieved through this cellar technique to 3.5% by volume and 2.5% by volume, depending on the wine region.

The basic rule is that 100 grams of sugar per liter increases the alcohol content of a liter by 0.66 percentage points.

Schiller Wine - Related Postings

German Wine Basics: How does a Sweet German Riesling Become Sweet?

Wine Ratings: Riesling Cup 2009 - Germany's Top Dry Rieslings

German Wine Basics: Erstes Gewaechs, Grosses Gewaechs, Erste Lage

1 comment:

  1. The last part must be wrong.

    "The basic rule is that 100 grams of sugar per liter increases the alcohol content of a liter by 0.66 percentage points."

    to reach 6.6% 1000g per liter is needed, or?