All too often, the language of wine generates frustration. Unpronounceable and untranslatable terms abound. But even the simplest words, like dry and sweet, can mislead a wine drinker. In fact, these two words are sometimes the most confusing.
Wine starts out as grape juice with plenty of natural sugar, principally fructose and glucose. Fructose is sweeter, and typically ferments more slowly than glucose. Once fermentation is completed, the sugars have been turned mostly into carbon dioxide and alcohol. But usually, some unfermented sugar remains. This is called residual sugar.
A finished wine’s “dryness” is determined by its residual sugar, measured as a ratio of weight to volume, usually grams per liter. But that alone does not determine how it will actually taste. A wine with 1 percent residual sugar (or 10 g/L) may seem quite dry if it’s a white wine with a lot of acidity, as might a red, if it’s high in tannins.
As a basic rule, wines with 10g/L or less of residual sugar are typically considered dry wines. (Most tasters cannot detect sweetness below 4 to 5 g/L.) At 10 to 24 g/L, wines are considered medium sweet or off-dry. Some decadently rich dessert wines reach ridiculous levels, with over 450 g/L or residual sugar. As a point of comparison, Coca-Cola has 108 g/L (about 11% residual sugar).
To dive more deep, the International Riesling Foundation defines four sweetness categories, based upon a sugar-to-acid ratio, with a further tweak dependent upon the pH of the finished wine. A linear scale that reflects these values is often printed on the back label of Riesling bottles. What’s helpful is that it acknowledges that sugar alone does not determine sweetness. Aromatic white wines like Riesling, Chenin Blanc and Gewurztraminer can balance residual sugar with higher total acidity, which gives an impression of dryness.
This is one reason why many wines, even those technically off-dry, can taste dry. And in some instances, dry wines may seem sweet. It has to do with how we perceive flavor.
And that is where things get more complicated.
Sweetness and Your Genetic Code
Tim Hanni, MW, has devoted his life to researching the history of sweet wines and the factors that affect sensory perception. He believes that people’s differing perceptions of sweetness are based on genetic phenotypes—actual physical characteristics that impact specific senses.
Single nucleotide polymorphisms (SNPs or “snips”) are common genetic variations. Think of them as your personal building blocks of genetic code. They strongly influence how you perceive alcohol.
For roughly 15 percent of people, alcohol tastes sweet, even at high levels. These are mostly males, and they have no trouble drinking wines with alcohol levels that would warm ordinary palates.
A more common SNP variation produces a warming sensation at moderate to high alcohol levels. For tasters with certain SNP sequences, anything over 12% to 13% alcohol is totally unpleasant—it literally burns. Those people, says Hanni, will never adapt to enjoy Scotch.
Alcohol is just one of several variables, or buffers, that impact the impression of sweetness, sugar aside.
Other Factors Influencing Sense of Sweetness
Tim Donahue, enology instructor at Walla Walla Community College in Washington, says that “a wine with 10 g/L residual sugar and 5g/L of total acidity will taste much sweeter than a wine with 30 g/L residual sugar, but a [total acidity] of 9g/L.”
Furthermore, says Hanni, “You can have two wines identical in residual sugar, acid and pH, and one tastes drier than the other, based on buffers inherent in the wine, along with individual genetics.”
Some buffers reduce the impression of sweetness, while others enhance it. Along with alcohol, glycerine can add non-sugar sweetness to the flavor. Acid and pH, tannins and potassium can do the opposite.
Even the chemistry of your saliva can have an impact, says Donahue.
“Depending on how your saliva transmits the chemical to your palate, and how much sodium, calcium and enzymes you have can all change your sweetness perception,” he says.
Tannins play an important role in perceptions of dry red wines. Tannins, says Hanni, are astringent and dry your mouth out, much like if you sucked on a tea bag. So a big red wine with heavy tannin levels might have residual sugar, yet feel dry. The tannins provide a sensory distraction that takes attention away from the sweetness.
“If someone is tickling the back of your neck and steps on your foot, you don’t notice the tickle anymore,” says Hanni.
The bottom line, says Hanni, “is that sweet is a category of tastes. Some artificial sweeteners taste metallic to some tasters. Others can’t tell a difference. There are other sweet compounds in wine that taste sweet, but are not measured by residual sugar. So that answers how a technically bone-dry wine may seem sweeter than a wine with twice as much [residual sugar]. The combination of alcohol, perception of alcohol and potentially sweet amino acids contribute to the perception of sweetness that is not measured by sugar.”
One more point: very ripe fruit can convey an impression of sweetness even in a wine that was fermented completely dry.
Put all of this together, and it’s clear that people must test their own taste buds to determine their personal benchmark for flavors they most enjoy.