Sugars in wine are at the heart of what makeswinemaking possible. During the process offermentation, sugars fromwine grapes are broken down and converted byyeast into alcohol (ethanol) andcarbon dioxide. Grapes accumulate sugars as they grow on thegrapevine through thetranslocation ofsucrose molecules that are produced byphotosynthesis from the leaves. Duringripening the sucrose molecules arehydrolyzed (separated) by the enzymeinvertase intoglucose andfructose. By the time ofharvest, between 15 and 25% of the grape will be composed ofsimple 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-carbonarabinose,rhamnose andxylose 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 anyresidual sugar). Sugar's role in dictating the finalalcohol content of the wine (and such its resultingbody and "mouth-feel") sometimes encourages winemakers to add sugar (usuallysucrose) during winemaking in a process known aschaptalization solely in order to boost the alcohol content – chaptalization does not increase thesweetness of a wine.[1]
Sucrose is adisaccharide, a molecule composed of the twomonosaccharides glucose, and fructose.Invertase is the enzyme cleaves theglycosidic 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 ofchaptalisation will be consumed in the fermentation. The exception to this rule isChampagne and othersparkling wines, to which an amount ofliqueur d'expédition (typically sucrose dissolved in a still wine) is added after the second fermentation in bottle, a practice known asdosage.
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 theripening 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 atharvest there are generally equal amounts. Grapes that are overripe, such as somelate harvest wines, may have more fructose than glucose. During fermentation, yeast cells break down and convert glucose first. The linking of glucose molecules withaglycone, in a process that createsglycosides, also plays a role in the resulting flavor of the wine due to their relation and interactions withphenolic compounds likeanthocyanins andterpenoids.[2]
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 grapeoverripens 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 sweetdessert 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 ofbrandy spirits in the process offortification) will be left with a wine that is high in fructose and notable residual sugars. The technique ofsüssreserve, where unfermented grapemust 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 ofchaptalization where sucrose (which is one part glucose and one part fructose) is added will usually not increase the sweetness level of the wine.[3]
Inwine tasting, humans are least sensitive to the taste ofsweetness (in contrast to sensitivity tobitterness orsourness) 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 asacidity andtannins can mask the perception of sugar in the wine.[1]
Flash release is a technique used inwine pressing.[4] The technique allows for a better extraction of winepolysaccharides.[5]
| Harvest | |
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| Pressing | |
| Maceration | |
| Fermentation | |
| Aging | |
| Other steps | |
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