Tag Archives: glucose

Sugar in Wine

Sugar plays a vital role in the wine in your glass, even if you can’t taste it directly.

ripe grapes

Ripe grapes

What is sugar?
Sugar is the name given to a wide range of carbohydrates, but only the simpler ones are sweet.

  • Glucose – one of the main products of photosynthesis in a plant, making up about 50% of sugars in ripe grapes. It is one of the three simplest types of sugar, known as monosaccharides. This is absorbed straight into the bloodstream during digestion.
  • Fructose – another monosaccharide, making up the other 50% of sugars in ripe grapes. It too is absorbed straight into the bloodstream during digestion.
  • Sucrose – the type of sugar you put in your tea, is typically produced from sugar cane or sugar beet, and very little is found in ripe wine grapes. Sucrose is in fact a combination of glucose and fructose.

Production of sugar in wine grapes
There is very little sugar in a grape until véraison, when the grape starts to change colour and ripen. Acidity decreases, and sugar contents rise, see the graph in a previous post. The trick is to get the correct balance between the two. Sugar concentrations in ripe grapes can easily achieve 20%.

Adding sugar manually

  • Before fermentation – sugar in grapes is converted to alcohol during fermentation, but if the grapes aren’t ripe enough, sugar may be added to artificially increase the alcohol content. A process known as chaptalisation. If this is done carelessly, there isn’t enough fruit in the wine to balance the relatively high alcohol. This practice is banned in many wine regions.
  • Adding two lots of sugar – Champagne manufacture involves adding sugar and yeast to produce bubbles in the bottle, and then sugar at the end to take the edge off the acidity.

Yeasts turn the simpler sugars into alcohol plus carbon dioxide, but many other reactions also happen, and some of the complex sugars remain.

Effect of residual sugar in wine

  • Tasting thresholdfor most people this is around 1% sugar content, but those who are particularly sensitive can detect 0.2%. A dry wine which is fully fermented out will have a sugar content of < 1.5 gm/litre, which is not detectable.
  • Balancing other tastessweetness balances acid and bitter tastes, making them less harsh.
  • Provides food for microbesresidual sugar in wine encourages bacterial growth unless it is properly protected. Sulphur dioxide is important here, see previous post.

In most wines, sugar just has a fleeting presence for a short while before the grapes are picked. It is created by photosynthesis, and consumed by fermentation.