Enrichment is the increase in sugar concentration of a must prior to fermentation, the objective being to increase the final level of alcohol of the wine. It must not be confused with sweetening, which is the addition of unfermented must or concentrate post-fermentation in order to sweeten the flavour of the final wine.
The advantages of enrichment are that it can render the wine more attractive to the customer (more balanced and full) and more microbially stable.

But first, let’s define a few terms:
Potential alcohol: the concentration of alcohol that would result from the total fermentation of the sugar dissolved in a must
Actual alcohol: the actual level of alcohol in a wine after fermentation
Residual sugar: the concentration of sugar left in a wine after an incomplete fermentation (or a sweetening operation)
Total alcohol = actual alcohol + potential alcohol from the residual sugar contained in a must or wine.
Natural alcohol: the total alcohol in an un-enriched must or wine.

Enrichment is carried out by the following methods:

• The addition of sucrose (chaptalisation), or concentrated must
• The concentration of the must by removing water through evaporation, ice formation or reverse osmosis filtration.

This practise is very strongly regulated in an effort to encourage vinegrowers to pick ripe grapes. In the European Union, the level of enrichment permitted depends on the zone in which the vineyard is situated.The UK, Benelux and most of Germany are in zone A, where:

• Sucrose (or concentrated grape must) may be added in order to increase the total alcoholic level of a must or wine by 3.0%. In poor years, the UKVA may request an extension of this to 3.5%.
• A wine may not have an actual alcohol content less than 8.5%
• The maximum level of total alcohol in an enriched wine may not be more than 11.5% for whites and 12% for reds and rosés
• Musts may not be enriched by concentrative methods by more than 2% or by a maximum reduction in volume of 20%, whichever is lower.
• Only one method of enrichment may be used on any wine, and wines enriched by different methods cannot be blended.

The use of sucrose is usually preferred, as it is the cheapest method, particularly as each kilogram of sugar increases the volume of the wine by 0.63 litres. Sucrose may not be dissolved in water prior to addition to the must.

In the UK, the intention to enrich the first wine of a vintage must be notified to the Wine Standards Board at least 48 hours prior to the operation. For more information on EU regulations on winemaking, see http://www.food.gov.uk/enforcement/sectorrules/winestandards/

Unfortunately, it is not possible to accurately predict the efficiency with which yeast will convert sugar to alcohol (it depends on yeast strain, level of yeast nutrients and temperature) but a reasonably good guide is to say that:

• For white wines: raising the level of alcohol by 1% by volume requires 17g sugar per litre
• For red wines, 19 g/l are required, due mostly to a higher level of evaporation at higher fermentation temperatures and in pumping over.

Concentrated Must or Rectified Concentrated Must’ (RCM: CM that has had its acidity neutralised and phenolics extracted) may be used instead of sugar. These are made of grape must concentrated by heat to give at least 58.2 w/w % sugar.