Sweetness in Wine

In the premium wine world, dessert wines and fortified wines are expected to be sweet. A few others, like Riesling and sparkling, can have various amounts of sweetness. The vast majority of table wines are meant to be dry with no discernible sweetness, but that's not always the case.

Not all sugars were converted,
so low alcohol, high sugars
in this dessert wine

Think of the sweetness as the opposite of acidic.

Grape sugars are changed to alcohol by fermentation, but if not all gets converted, you can have enough residual sugar to get a sweet wine. The more sugar left, the sweeter the wine. About 0.5% RS is where you can start to pick up the sweetness. Other factors, such as tannins, can partially mask it. 

If the grapes are very ripe and aromatic, you can perceive the fruity notes of the wine as sweetness. That often happens in young wines such as Zinfandel. That bright red fruity flavor is perceived as sweetness by the brain because ripe fruit is sweet.

Alcohol can taste sweet and sometimes hot, so higher alcohol wines can give a sweetness.

Many find a sweetness in their drink as pleasant, so this is often done on purpose, and it's not just cheaper wines. A number of high-end California wines are suspected of having RS, though the winery would never admit to it.

A number of years ago, I worked for a small winery and had a few regular customers asking if we still had any of a specific 2005 Zinfandel. I asked the winemaker abut this wine, he said that was a stuck fermentation, meaning the yeast would not convert all the sugars to alcohol, and the wine came out at about 3% RS. Some people loved it!

I mentioned the vintage year of the wine because 2005 was a year of many stuck fermentations. I don't know if anyone figured out why. Weird, huh?