Dry and Sweet Wines: Understanding Residual Sugar, Tannins and Acidity
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Dry and Sweet Wines: Understanding Residual Sugar, Tannins and Acidity

What makes a wine sweet or dry. How residual sugar, acidity and tannins affect how we perceive a wine's sweetness or dryness. How sugar, acidity and tannins balance to create a pleasing wine. When wines with a high residual sugar will taste drier than wines with a lower sugar. How our palates perceive what is sweet or dry.

A while back, I had written an article entitled "Wine Tasting 101:  Fruitiness Does Not Equal Sweetness" that, while providing a solid foundation in understanding the differences between fruity wines and sweet wines,did not discuss what determines a dry or sweet wine.  This article explains the roles that residual sugars, tannins and acidity play in measuring the dryness or sweetness of wine.

The sweetness of a wine is actually a somewhat subjective term, though it is also based on several measurable and interact-able factors:   

  • Residual sugars are sugars that are left in the wine once the fermentation is complete.  When making wine during the fermintation process, sugars are broken down by yeast and converted into alcohol.  All wines, including dry wines, will have at least some residual sugar left as not all sugars can be converted into alcohol.   The residual sugars will enhance a wine's sweetness and is measured in grams of sugar per litre of wine (g/l), though in the U.S. sugars may be measured with the Brix system.   In addition, some winemakers will add additional sugar to their wines at the end of fermentation so they can create a wine that is both sweet and high in alcohol content.  Generally speaking, wines that have less than 4 g/l are considered dry whereas wines that contain greater than 45 g/l are considered sweet.  However, there is more to determining the dryness or sweetness in a wine than the measurement of residual sugar.  The way these sugars interact with other factors in the wine will also impact our perception of sweetness, meaning that some wines with comparatively higher levels of residual sugar will taste drier - and will be considered drier - than wines with a lower residual sugar.  A wine's acidity and its levels of tannin also interact with the residual sugars and help determine the dryness or sweetness in a wine.
  • Acidity in wine is an important factor in appreciating the taste, quality and feel of the wine in the mouth. It can give both the taste and sensation of sharpness, tending to balance the sweetness of a wine.  Wines with little acidity tend to taste flat, bland and with a less distinctive flavor, whereas wines with higher acidity can be extremely sharp or "hot" on the tongue and in the mouth, often leaving a sour or spicy impression.  Finding the balance between acidity and sugar is imperative to making good wine. As grapes ripen, their levels of sugar increase while their acidity decreases.  Grapes from cooler climates also have higher acidity levels than grapes from warmer climates as it takes longer for grapes to ripen.  Acidity is therefore an important determination among harvesters in choosing when to pick the grapes.  Just as winemakers will sometimes add sugar to a wine to get a wine that is both sweeter and higher in alcohol, they will also occassionally add acids to a wine in order to balance its sweetness, especially if the wine came from grapes that were harvested later or had ripened earlier than expected (often due to changes in climate and weather).  This can happen either before or after primary fermentation, or in the later stages of wine production such as blending or aging.  As a general rule, if acids are added in the later stages of production, they tend to be more noticeable on the palate.  
  • Tannins, including tannic acids, are astringent and bitter properties found in many plants which are responsible for the ripening of certain fruits and the aging of wine.  Citric fruits do not contain tannins, whereas many other fruits, fruit juices (including juices made from citric fruits as these contain dyes made from tannins), teas and wines will contain tannin.  Some ciders have added tannin in order to give it a more astringent feel in the mouth.  It should be noted that tannins have potential antiviral and antibacterial properties.  Along with sugars and acids, tannins help give wine its flavor, fullness and balance, primarily as a contrast to sugars and acidity.  The bitterness of tannins help counteract a wine's sweetness, sourness and/or spiciness.  How sweet or dry a wine tastes is therefore affected by tannins.  A wine with a high amount of residual sugar may taste remarkably dry if it also has a high level of tannins.  Red wines tend to have more tannins than white wines, while red meat and other high protein foods are often paired with tannic red wines in order to balance and compliment the flavor and feel of both wine and meat.

According to a 2002 EU regulation, the sweetness of a wine can be measured by the following levels of residual sugar, both with and without relation to acidity:

  • Dry - up tp 4 g/l
  • Medium Dry - up to 12 g/l
  • Medium Sweet - up to 45 g/l
  • Sweet - above 45 g/l

When balanced with acidity, the chart becomes:

  • Dry - up to 9 g/l
  • Medium Dry - up to 18 g/l
  • Medium Sweet -  (not applicable)
  • Sweet - (not applicable)

Most winemakers, at least in the U.S., are loathe to add information regarding residual sugars to their wine labels.  This is due in part because they realize their typical consumer does not understand there is more to determining the sweetness of a wine than just the residual sugar amounts, while also understanding that many consumers are loathe to try a wine they believe is sweet.  It should also be remembered that when tasting wine, we are generally least sensitive to its sweetness and are more likely to notice its bitterness, sourness or spiciness.  This also affects why many wines will have a higher residual sugar and not be considered a "sweet" wine. 

I hope you enjoyed this article.  You may also enjoy the following articles regarding wine:

Wine Tasting 101: Fruitiness Does Not Equal Sweetness

Meritage Wine:  America's Bordeaux-styled Blend

Top 5 California Zins for Under $20

Cinsault & Mourvedre, Red Wine Grapes for a Beautiful Bouquet

"Anything but Chardonnay?" Learning about Chardonnay and an alternative, Viognier.

WSJ Wine Review — Wine Clubs Comparison (2012)

Health Benefits of Red Wine: What's Real and What's Hype?

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