What Type of Sugar is in Grapes?

October 26, 2025 •

3 min read

Ripe grapes can contain up to 250 grams of sugar per liter, and that sweetness comes predominantly from two monosaccharides, glucose and fructose. A smaller, though still significant, amount of sucrose is also present, which breaks down into these two simple sugars as the fruit ripens. These sugars contribute to the grape's taste and are critical for the wine-making process.

Quick Summary

Grapes contain a significant amount of natural sugars, primarily glucose and fructose, with trace amounts of sucrose and other complex sugars. The ratio of glucose to fructose shifts during ripening, affecting the fruit's sweetness. These sugars are fundamental to the grape's flavor profile and play a vital role in winemaking.

Key Points

Glucose and Fructose: Grapes contain two main simple sugars, glucose and fructose, which are present in roughly equal amounts in ripe berries.
Sucrose is a Minor Component: While sucrose is the transport sugar from the leaves, it is quickly broken down into glucose and fructose, so it's only present in trace amounts in ripe grapes.
Ripening Changes Sugar Ratio: The ratio of glucose and fructose changes during ripening, with glucose dominating in unripe grapes and fructose potentially exceeding glucose in overripe ones.
Sweetness Differences: Fructose is significantly sweeter than glucose, which explains why overripe grapes and certain sweet wines can taste particularly sugary.
Sugar is Fuel for Fermentation: In winemaking, the grape's sugars are fermented by yeast to produce alcohol; a higher sugar content in the grapes results in a higher alcohol content in the final wine.
Variety and Climate Affect Sugar: The final sugar concentration and the glucose/fructose ratio can vary significantly between different grape varieties and are influenced by growing climate.

The Major Sugars: Glucose and Fructose

In grapes, the main sugars are glucose and fructose, which are both simple sugars, or monosaccharides. They are easily absorbed by the body and provide a quick source of energy. These two sugars make up the vast majority of the soluble solids in grapes and are crucial for determining the fruit's ripeness.

The Ripening Process and Sugar Content

As grapes mature on the vine, the ratio of glucose to fructose changes. In an unripe grape, glucose is the more dominant sugar. As the berry ripens, the enzyme invertase breaks down sucrose—which is a disaccharide made of one glucose molecule and one fructose molecule—into its component monosaccharides. This process shifts the sugar composition, and by the time the grape is fully ripe, glucose and fructose are typically present in nearly equal amounts. In some overripe grapes, fructose concentration may even exceed that of glucose.

The Role of Sweetness

Fructose is significantly sweeter than glucose. On a relative sweetness scale where sucrose is 100, fructose measures around 120–180, while glucose is around 70–80. This difference in sweetness is why the flavor profile of a grape changes so dramatically throughout its ripening cycle. A higher proportion of the sweeter fructose in an overripe grape makes it taste even more sugary. This difference in sweetness is also critical for winemakers, as a wine high in residual fructose will taste sweeter than one with a similar level of residual glucose.

The Minor Sugars: Sucrose and Pentose

While glucose and fructose are the major players, other sugars are present in grapes, though in much smaller quantities.

Sucrose: This disaccharide is present in trace amounts in most grape cultivars, contributing less than 1% of the total sugars. However, some hybrid varieties of grapes, such as those from Vitis rotundifolia or certain Vitis labrusca and Vitis vinifera hybrids, can have notably higher sucrose content.
Pentose Sugars: These are five-carbon sugars, including arabinose, xylose, and rhamnose. Pentoses are not easily fermentable by yeast, so they often remain in the wine after fermentation is complete. They have a low relative sweetness and do not contribute significantly to the perceived sweetness of the final product.

Comparison of Sugars in Grapes


Sugar Type	Category	Chemical Composition	Metabolism	Role in Grapes
Glucose	Monosaccharide	Six-carbon ring, aldohexose	Primary energy source for the body; fermented first by yeast	Predominant in unripe grapes, balances with fructose in ripe grapes
Fructose	Monosaccharide	Six-carbon ring, ketohexose	Metabolized primarily in the liver; fermented after glucose by yeast	Higher concentration in overripe grapes; significantly sweeter taste
Sucrose	Disaccharide	One glucose + one fructose molecule	Broken down by invertase during digestion and ripening	Trace amounts in most ripe grapes; more common in certain hybrids
Pentoses	Monosaccharides	Five-carbon sugars (e.g., xylose, arabinose)	Poorly metabolized by yeast and humans	Trace amounts; remain in wine as unfermentable residual sugars

Significance in Winemaking

The composition and quantity of sugar in grapes are paramount for winemaking. The level of sugar, measured in units like °Brix, is the primary factor determining a wine's potential alcohol content. During alcoholic fermentation, yeast consumes the sugars and converts them into alcohol and carbon dioxide.

Sugar Level and Alcohol Content: The riper the grape, the higher the sugar content and, consequently, the higher the potential alcohol in the finished wine.
Yeast Preference: Yeast ferments glucose preferentially over fructose. If fermentation is stopped early, more fructose will remain, resulting in a sweeter-tasting wine since fructose is sweeter than glucose.
Chaptalization: In cooler climates where grapes may not ripen fully, winemakers may add sugar (sucrose) to the must to increase the final alcohol content, a process known as chaptalization.

Conclusion

Ultimately, the sweetness of a grape comes from a combination of different sugars, with the main contributions from glucose and fructose. Their balance shifts as the fruit ripens, which is why the flavor of a grape evolves from unripe to overripe. This nuanced sugar profile is not only vital for the taste of the fresh fruit but also forms the foundation of one of humanity's oldest fermented beverages. Understanding what type of sugar is in grapes provides deeper insight into both fruit chemistry and the complex art of winemaking. For further details on grape composition and winemaking, you can explore resources like the Iowa State Extension Wine Growing articles.

Frequently Asked Questions

The sugars in grapes are natural fruit sugars (glucose and fructose). While high consumption of added sugars is unhealthy, the sugars in whole fruit like grapes come with fiber, vitamins, and antioxidants, which slow absorption and offer nutritional benefits.

Yes, grapes have a relatively high sugar content compared to many other fruits. The sugar concentration can vary depending on the grape variety and ripeness, with some containing up to 250 grams of sugar per liter.

Sugar content in grapes is commonly measured using units like °Brix. This measurement indicates the concentration of soluble solids, which are predominantly sugars, in the grape juice.

Yes, the sugar content increases as grapes ripen. During ripening, sucrose is converted into glucose and fructose, and the ratio of these two sugars changes from more glucose to a more balanced mixture, or even more fructose in overripe grapes.

In winemaking, yeast consumes the glucose and fructose in the grape juice and converts them into ethanol and carbon dioxide during fermentation. The amount of sugar in the grapes directly influences the final alcohol content of the wine.

Most of the glucose and fructose in grapes are fermentable by yeast. However, trace amounts of other sugars, like five-carbon pentose sugars (xylose, arabinose), are not easily metabolized by yeast and remain in the final wine.

Some wines taste sweeter than others due to their residual sugar content. Winemakers can halt fermentation early, leaving more unfermented fructose—which is sweeter than glucose—in the wine. This creates a sweeter-tasting wine with a higher residual sugar content.