Tag Archives: grapes

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.

Fermentation
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.

Conclusion
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.

Sulphur Dioxide – the Magic Molecule

Sulphur Dioxide molecule

Sulphur Dioxide molecule

Sulphite additions to food and wine have become a big issue. However, the sulphites, and the sulphur dioxide that they produce have real benefits.

Why is the term sulphite used?
Sulphur dioxide is sometimes injected as a gas, but solid sulphite granules are usually added instead. The acid in wine rapidly splits this up to produce sulphur dioxide which actually does the work.

Sulphur dioxide occurs naturally in wine
This may seem unlikely, but fermentation of grapes produces sulphur dioxide without any help from humans. The amount depends on the the yeasts that are used, but it is a ‘natural’ product.

Why are sulphites added to wine?
There are two main benefits:-

  • Antioxidantif wine is exposed to air, the alcohol is quickly oxidised to acetic acid (vinegar). So, nature’s natural tendency needs to be moderated, if we are to drink the wine before it goes off. Sulphur dioxide attacks the chemicals which would otherwise produce vinegar. This is less of an issue for red wines which have their own antioxidants.
  • Antimicrobial – wine contains yeasts and bacteria. The magic molecule prevents these from multiplying and spoiling the wine.

Which wines have the most sulphur dioxide?
SO2 binds with many compounds in wine, including sugar. Only the unbound sulphur dioxide is able to fend off oxygen and microbes. So, sweet wines need plenty to protect them.

The importance of quality grapes
Rotten grapes make rotten wine, and need more sulphur dioxide to keep the bugs under control. Grapes with plenty of acidity also need fewer additions.

What are the adverse effects?

  • Sensoryan excess of sulphur dioxide produces a smell of burnt matches, but an awful lot needs to be added to have this effect. This fault is rare.
  • Healthis a difficult issue because there is little proof of adverse effects. It may induce asthmatic attacks in some people. It is worth noting that normal food metabolism in the body generates much more sulphites than you would absorb from wine consumption.

Conclusion
In my opinion, the addition of sulphites at the right time and in the right quantity is beneficial, if not essential, for almost all wine.