When you think about sugar in wine it's not exactly like the sugar you bake your chocolate chip cookies with. It's natural residual sugar from the fruit that didn't get converted by the yeasts during the fermentation process. So yes. There can be sugar in some wines, but it just depends on the style of wine.
Wines With Low Sugar Content
So what are these low sugar wine options? First of all, stay clear of dessert wines, like moscato d'Asti, eiswein, and Sauternes. These have obvious higher levels of sugar that you can definitely taste, adding up to well over 120g/L. Look for dry reds and whites that have less than 1% residual sugar or under 10g/L. Here's where it gets tricky. This isn't listed on the label. Sigh. You'll need to search out the tech sheet for the specific wine to find out just how much sugar may or may not be in the wine. Often, a winemaker will upload this technical information about the wine on their website, so start there.
If you are out at a restaurant and browsing a list, ask the somm to guide you towards dry wines. Most wines are fermented to dryness so there are generally a lot of options. Dry muscadet, Chablis, sauvignon blanc, cabernet franc, carignan, Rioja, pinot noir, and tempranillo are all on the low end of the wine calorie spectrum and are great options to pour up if you are avoiding sugar.
Measuring Residual Sugar
The sugar content in wine is a measure of residual sugars left behind during the fermentation process. The residual sugars in wine are those sugars that don't convert to alcohol and carbon dioxide as part of the wine's fermentation process. In general, the residual sugar content after fermentation is inversely proportionate to the alcohol level. This means that higher alcohol wines have less sugar, and lower alcohol wines have more sugar.
Most wines don't contain much residual sugar; however, many wines do have very small amounts of residual sugar left after the fermentation process. Vintners measure residual sugar in wine in grams per liter. The abbreviation for this is g/L. Most wines--even the driest of wines--have at least one gram per liter of residual sugars after fermentation. Amounts less than 10g/L and are not detected by most palates, so they are considered dry wines.
Factors Affecting the Sugar Content in Wine
There are a number of factors that affect the final amount of sugar that winds up in wine. First and foremost is the sugar content of the grape. Some grapes are naturally higher in sugar than others.
Another factor is how late in the season the grapes are harvested. The longer the grapes hang on the vine, the more concentrated the sugars become. This process is very evident in the classification of German riesling wines, which are harvested at different times during the season. The later the harvest, the higher the sugar is in the grapes--and ultimately the wine. In the vineyard, the sweetness or ripeness of a grape is measured using the Brix scale. Brix measures the sugar content in the grapes, and it is a very important factor in choosing when to harvest.
The final piece that can affect the overall sugar content in a wine is the style of wine the vintner is aiming to make. In the cellar, they will choose to let the fermentation run its course, leaving little to no residual sugar or, they can halt the fermentation process mid-way if they are creating a sweeter style wine.
Look for Dry Wines
If you are looking to avoid added sugar, search out dry wines. You can easily find a red, white, rosé, or orange wine that will fit the bill. If you have access to the tech sheet and feel like getting all scientific, take a look and see just how little or how much sugar is in any given bottle.