Do All Wines Contain Sugars?

Let's set the record straight: At the end of the day, wine is nothing but fermented grape juice. That means, whether you like it or not, sugar — more specifically, the residual sugar left post-fermentation — is a part of the deal.

The good news is not all wine boasts the same amount of sugar. A bone-dry bottle can have less than one sugar calorie per glass, making it nearly impossible for most people to detect it. Meanwhile, a very sweet wine, such as France's iconic Sauternes, can have more than 130 sugar calories per glass. Out of those that fall somewhere in the middle, dry wines contain up to six sugar calories per glass, off-dry wines vary between six and 21, while sweet wines can go as high as 72. 

But, which factors actually determine a wine's sugar content? It all comes down to the grape variety, the fermentation process, and a few other aspects, including the wine's style and the winemaker's production decisions.

You might have heard that all wines start in the vineyard. Therefore, the grape variety and its unique characteristics significantly influence a wine's sweetness. For example, Muscat of Alexandria grapes are so naturally sweet that they're mostly used to produce rich, sweet wines, with just a few dry versions available out there. On the other hand, white grape varieties like Chardonnay, Sauvignon Blanc, and Pinot Gris are considered ideal for producing superb dry wines praised for their crispness and minerality.

Fermentation is another key factor influencing the amount of residual sugar left in wine. During this anaerobic chemical process, yeast converts grape sugars — primarily simple glucose molecules – into ethanol (alcohol) and carbon dioxide. Usually, fermentation stops naturally when the yeast (most commonly Saccharomyces cerevisiae) consumes all available grape sugars in the must. This gradually reduces the wine's residual sugar content, resulting in a much drier wine. 

However, winemakers may sometimes intentionally stop the fermentation early to preserve some residual sweetness by leaving some of the sugars unconverted. A typical example of this is Portugal's famous Port wine, a sweet fortified wine produced by intentionally halting the fermentation through the addition of a neutral grape spirit.

While you can do some research and find out how much sugar is in a single glass of red wine, detecting the actual residual sugar content can be surprisingly tricky, even for highly trained wine connoisseurs. That's why the next best thing you could do is to simply check the wine label on the back of the bottle.

However, since disclosing residual sugar levels on their labels isn't a legal requirement for wineries, you'd be surprised how many skip that little detail. Nevertheless, a large portion of well-known brands are usually transparent with these figures.

If the residual sugar information is provided on the label, you'll usually see it listed in grams per liter. You could also find it expressed in grams per 100 milliliters or as a percentage. The label might also specify whether a wine is dry, semi-dry, or sweet, which is also a useful clue as to the amount of residual sugar.