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Sugars in wine

Sugars in wine is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sugars in wine rather than just read about it. In short: Sugars in wine are at the heart of what makes winemaking possible. During the process of fermentation, sugars from wine grapes are broken down and converted by yeast into alcohol (ethanol) and carbon dioxide.

Sugars in wine — main illustration
Sugars in wine — illustration

Key takeaways

  • Sugars in wine belongs to chemistry; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Sugars in wine to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Sugars in wine from memory before moving on to harder problems.

Reference excerpt

Sugars in wine are at the heart of what makes winemaking possible. During the process of fermentation, sugars from wine grapes are broken down and converted by yeast into alcohol (ethanol) and carbon dioxide. Grapes accumulate sugars as they grow on the grapevine through the translocation of sucrose molecules that are produced by photosynthesis from the leaves. During ripening the sucrose molecules are hydrolyzed (separated) by the enzyme invertase into glucose and fructose. By the time of harvest, between 15 and 25% of the grape will be composed of simple sugars. Both glucose and fructose are six-carbon sugars but three-, four-, five- and seven-carbon sugars are also present in the grape. Not all sugars are fermentable, with sugars like the five-carbon arabinose, rhamnose and xylose still being present in the wine after fermentation. Very high sugar content will effectively kill the yeast once a certain (high) alcohol content is reached. For these reasons, no wine is ever fermented completely "dry" (meaning without any residual sugar). Sugar's role in dictating the final alcohol content of the wine (and such its resulting body and "mouth-feel") sometimes encourages winemakers to add sugar (usually sucrose) during winemaking in a process known as chaptalization solely in order to boost the alcohol content – chaptalization does not increase the sweetness of a wine.

Sucrose

Sucrose is a disaccharide, a molecule composed of the two monosaccharides glucose, and fructose. Invertase is the enzyme cleaves the glycosidic linkage between the glucose and fructose molecules. In most wines, there will be very little sucrose, since it is not a natural constituent of grapes and sucrose added for the purpose of chaptalisation will be consumed in the fermentation. The exception to this rule is Champagne and other sparkling wines, to which an amount of liqueur d'expédition (typically sucrose dissolved in a still wine) is added after the second fermentation in bottle, a practice known as dosage.

Glucose Glucose, along with fructose, is one of the primary sugars found in wine grapes. In wine, glucose tastes less sweet than fructose. It is a six-carbon sugar molecule derived from the breakdown of sucrose. At the beginning of the ripening stage there is usually more glucose than fructose present in the grape (as much as five times more) but the rapid development of fructose shifts the ratio to where at harvest there are generally equal amounts. Grapes that are overripe, such as some late harvest wines, may have more fructose than glucose. During fermentation, yeast cells break down and convert glucose first. The linking of glucose molecules with aglycone, in a process that creates glycosides, also plays a role in the resulting flavor of the wine due to their relation and interactions with phenolic compounds like anthocyanins and terpenoids.

Fructose

Fructose, along with glucose, is one of the principal sugars involved in the creation of wine. At time of harvest, there is usually an equal amount of glucose and fructose molecules in the grape; however, as the grape overripens the level of fructose will become higher. In wine, fructose can taste nearly twice as sweet as glucose and is a key component in the creation of sweet dessert wines. During fermentation, glucose is consumed first by the yeast and converted into alcohol. A winemaker that chooses to halt fermentation (either by temperature control or the addition of brandy spirits in the process of fortification) will be left with a wine that is high in fructose and notable residual sugars. The technique of süssreserve, where unfermented grape must is added after the wine's fermentation is complete, will result in a wine that tastes less sweet than a wine whose fermentation was halted. This is because the unfermented grape must will still have roughly equal parts of fructose and the less sweet tasting glucose. Similarly, the process of chaptalization where sucrose (which is one part glucose and one part fructose) is added will usually not increase the sweetness level of the wine.

In wine tasting

In wine tasting, humans are least sensitive to the taste of sweetness (in contrast to sensitivity to bitterness or sourness) with the majority of the population being able to detect sugar or "sweetness" in wines between 1% and 2.5% residual sugar. Additionally, other components of wine such as acidity and tannins can mask the perception of sugar in the wine.

Flash release Flash release is a technique used in wine pressing. The technique allows for a better extraction of wine polysaccharides.

See also Gluconic acid – an acid sugar found in wine

References

Illustrations

Sugars in wine: The sugars in grapes are stored in the pulp along with water, organic acids and other compounds
The sugars in grapes are stored in the pulp along with water, organic acids and other compounds
Sugars in wine: In wines like Port, the addition of neutral grape spirits stuns the yeast and halts fermentation, leaving a wine with a higher proportion of fructose sugars and creating a sweet wine.
In wines like Port, the addition of neutral grape spirits stuns the yeast and halts fermentation, leaving a wine with a higher proportion of fructose sugars and creating a sweet wine.

Worked examples

Example 1 — a first encounter with Sugars in wine

Start with the simplest possible case. Write down what Sugars in wine claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sugars in wine before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sugars in wine ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sugars in wine

In research
Sugars in wine appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Sugars in wine in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Sugars in wine is common in secondary-school and first-year university syllabi. It links to neighbouring topics Carbohydrates, Sugar, Wine chemistry, so understanding it makes those chapters shorter.
In everyday life
Look for Sugars in wine outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study Sugars in wine in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Sugars in wine means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Sugars in wine out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sugars in wine in simple terms?

Sugars in wine are at the heart of what makes winemaking possible. During the process of fermentation, sugars from wine grapes are broken down and converted by yeast into alcohol (ethanol) and carbon dioxide.

Why does Sugars in wine matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sugars in wine?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sugars in wine.

Tags

  • Carbohydrates
  • Sugar
  • Wine chemistry

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