I was recently told that pinot noir is the sweetest red wine. Likewise, I have many times been subjected to such statements as “rieslings are sweet”, or “gewürztraminer is a sweet wine”, or “I don’t like rosé, it is too sweet”. These sweeping statements of varietal sugar content simply do not stand up to scrutiny. To which, I have chosen ‘sugar in wine’ as this week’s For The Vin post. To begin the examination of wine’s sweetness, we have to explore the actual sugar content of both the final product wine, as well as the grapes they derive from. As well, other components of wine influence how the residual sugar is perceived. Tannin, acidity and aroma, all play a part in the perception of sweetness in wine, so it is important to understand flavor contrast in addition to the role of the olfactory in discerning sweetness.
Sugar comes in many forms. The main sugars in grapes are glucose and fructose. These sugars are what the alcohol in wine is made from during fermentation. Yeast eats sugar, and in the process releases alcohol, heat, and carbon dioxide. The sugar content of the grapes at harvest depends on the ripeness of the fruit, as well as the variety of the grape. The ripeness depends on weather, more than any other factor. Grapes, like all fruit, have sun requirements to produce their fruit and bring it to its full ripeness potential. In warmer wine regions, this is not an issue because there is no shortage of sun or race against the end of the season. In cooler climate regions, there can be a balancing act of harvesting at the most ripeness possible, and risking losing the crop to frost. Each variety of grape has a slightly different sun and length of season requirement. These variations of need are the result of natural and human selection over time. Riesling has been grown in Germany, a cooler climate region, for a long time and can thrive in those climatic conditions. A grape such as touriga nacional can happily produce fruit in hot and dry conditions, but would not likely fare well in the hills of The Rhine. At least not every season. So, the sugar content of the grape at harvest (usually measured on either the Brix scale or in degrees Oechsle), gives the wine its alcohol level possibility. As yeasts feed on the available sugar, the alcohol content rises. Eventually, one of three scenarios will conclude the fermentation.
The first is that all (most) of the sugar gets eaten up, and the yeast runs out of fuel. This results in a bone dry wine, meaning there is little to no residual sugar in the wine. The second is that there was a very high sugar content at harvest, and the yeast converts the sugar to alcohol until the alcohol level gets too high, the yeast dies, and the fermentation ends. Different yeast strains have varying tolerances for alcohol environment, but most will not live past 17 or 18% ABV (alcohol by volume). Some strains can not even live past 12% ABV. Any sugar remaining, called RS (residual sugar), will add some level of sweetness to the wine.
The final scenario is human intervention. Fermentation can be stopped by a drastic reduction in temperature, or by adding sulfites or alcohol. Any remaining sugar will, once again, add sweetness to the wine.
Looking at some of the examples in the opening statement, riesling, pinot noir and gewürztraminer are all varieties that have traditionally been grown in the cooler weather regions of Germany, Austria, and mid to northern France, although they are now world travelers and can be found in Australia, Napa, and Chile, to name a few more southern ones. All three of these varietals are more likely to be made in the style of the first scenario. That is, most of the sugar is consumed by the yeast and the resulting wine is dry. There are many examples of riesling and gewürz that are sweeter due to the third scenario, human intervention, but this practice takes more effort than just letting the wine fully ferment naturally and completely, and is less common than the dry versions. The main confusion of sweetness with the aromatic wines, like gewürz or one of the muscats, comes from the fruitiness. The terpenes that add ripe fruit & tropical fruit and floral aromas to the wine, give it the impression of sweetness whether it has a high sugar content or not. If the wine was made sweet by preventing the completion of the fermentation, the alcohol content will be a little lower than a fully fermented one. A lower ABV could also be indicative of lesser ripened fruit but is most likely the result of this process. These fruity scents that give the aromatic varietals a sweet reputation are really a trick of our brain associating fruity with sugar. The pinot noir example is a little different and has more to do with tannin than with aromatics. There is a common misunderstanding of the dry to sweet scale of red wine. That is, the confusion between tannic and dry. Having a lot of tannins, or having unripe and immature tannin, does give a drying, puckering feeling to your mouth, much like an over-brewed black tea. This is not, however, what is referred to as dry, in wine. Dry is the absence of sugar and is not related to tannic structure. Pinot noir is a thin-skinned grape, and thus imparts less tannin to wine than some of its thicker-skinned cousins. There are other factors that affect the extraction of tannin and how much remains in the wine you are drinking, and how affecting that tannin is on the flavor, but beginning with less in the grape is of course a contributor. This lighter tannin trait is then associated with less dry, giving rise to the misnomer of sweet. Pinots are in fact most often very dry wines, but with lighter-than-some tannins, particularly in the old world regions where they originate. The reds that are more likely to hide a lot of sugar are from the higher tannin varieties that are grown in warm climates to a very ripe stage. California cabs or Australian shiraz, can house high grams per liter sugar(g/L), but not seem overly sweet because of their bold tannins.
Another factor in your perception of sweetness is the balance of acidity to sugar. The acids in wine help to preserve it, open up the palate to the flavors and balance out the other components. The perception of the alcohol, the tannin, and particularly the sweetness, are all affected by the level of acidity. The higher the acidity, the less you detect the sugar. To remain in balance, a high acid wine requires some sugar to taste good. Conversely, a high residual sugar content will not taste as sweet if the acid level is high enough to balance it.
Sweet wines require specific conditions or additional processes to concentrate the sugars. Some wines are traditionally left with a small amount of sugar to lightly raise the sweetness, though there are examples of wines that are extremely sweet. There are several methods for creating sweet wines. As mentioned earlier, the fermentation can be aborted by dropping the temperature or by adding a preserving agent. This is common practice for many German rieslings, and other Germanic varieties, and gives rise to the notion that riesling is sweet. It is, however, the method as opposed to the grape variety, which results in the raised RS. There are more 'dry to off-dry rieslings than sweet ones, produced in Germany. Around the world, there are far more dry than sweet rieslings.
Adding spirits to stop fermentation before all the sugar is converted to alcohol, called fortifying, is the method used to make Port, Sherry, and Madiera wines. These fortified wines have a lot of residual sugar, up to and sometimes