What makes wine sweet is intuitive: sugar. That is to say, naturally occurring sugar—mostly fructose, but glucose to an extent too. Glucose is more readily consumed by yeast than fructose is. But what makes a wine dry? Essentially, it is the lack of sugar. The more of the sugar from the juice that the yeast consumes—and converts to alcohol—the drier the resultant wine. This is how white wines can range from drier examples such as our 2018 Chardonnay, Ram's Gate Estate to much sweeter ice wines. Along the red dry-sweet spectrum are cabs and pinots like our 2018 Cabernet Sauvignon, Bismark Vineyard, or our 2018 Pinot Noir, Sonoma Coast for drier options to ports and tawny ports for sweet red wines.
The more residual sugar there is in a wine, the sweeter it is. This can be confusing to many people because one person's sensitivity to tasting present sugar is rarely the same as the next person's. Additionally, some varietals may have a "sweeter" character than others so a dry variety of one could taste sweeter than the sweet variety of another. But for the most part, sweeter wines still have residual sugar in them. This is how you can have both a dry and a sweet riesling. This is not the result of winemakers adulterating the natural fermentation process—it's illegal to add sugar to California wine—but the winemakers' expressions of the natural character of the grapes.
Another factor impacting wine's final resting place on the sweet-dry spectrum is when the grapes get harvested. Grapes harvested later had more time to ripen and develop sugar content. Those lead to sweeter wines unless the winemaker also increases fermentation time. The longer it ferments, the more time the yeast has to convert sugar to alcohol. Now you have an idea what to expect when you see "late harvest" California wines. The odds are those will be sweeter than their counterparts.
What Makes Wine Dry?
So, what makes a wine dry then? It's still a liquid after all. It's really just the opposite of sweet wine. A descriptor. Some people say that certain wines leave their mouths feeling dry after drinking them. This is not the same as wine that is dry. That dry feeling you're experiencing is caused by higher levels of tannins in the wine and not a result of no residual sugar. Acidity can also make a wine drier. Immature grapes have less sugar and more acidity so this follows well with what we've learned already: more acidity likely means less sugar.
Finally, more alcohol also makes wine drier. This also makes sense because the yeast converted more sugar into more alcohol. So if you see higher alcohol by volume (ABV) on one bottle than another, then you're probably looking at a drier option.
Which Is Better?
Well, that all depends. First and foremost, it's important to remember that the best wines are the ones you enjoy drinking. Regardless of what anyone else tells you about a wine's merits, if you don't like it then it's not for you.
Secondly, context goes a long way with choosing a good wine. What is the occasion? Are you looking to have wine and charcuterie? Or is the wine intended for a meal pairing? You don't want your selection to overpower the dish, but neither do you want to underwhelm the diners. Pairing wine and meals is a large enough topic on its own. But if it's just a simple apéritif or digestif the choice is a little easier. If the former, go with dry and whet your diners' appetites; if the latter, choose a sweet dessert wine.