The basic process of creating wine relies on yeast organisms eating natural sugars found in the grape pulp and liquids, thereby fermenting and releasing alcohol and C02 as by products.
Even when a wine is considered dry, there is always a little sugar in it. This is because yeast cells that turn sugar into alcohol and CO2 will die when the alcohol reaches a higher percentage during the fermentation process, thus not fermenting completely dry and leaving residual sugar.
The question is how much sugar is left and how do we classify wines according to this? Let’s begin looking at how the sugar is made in the plant during photosynthesis. The plant produces 3 main sugars through photosynthesis. Sucrose in the vine’s leaves is transported to the berry where it hydrolysed(separated) by an enzyme called invertase in the grape to become glucose and fructose that are important for fermentation (see info graphic).
As the grapes ripen they initially have low levels in sugar until it reaches a stage where there is a drastic change in the metabolism of the berry and it becomes a sugar accumulating organ, collecting glucose and fructose. This process is affected by the amount of sunlight.
These different levels of sugar accumulation define certain classes of wine such as Dry, Semi-Sweet and Late Harvest. The different classes and the amount of residual sugar that defines them are listed in the table below.
Most of the boutique wines that we sell are classified as Dry with 5 grams of sugar or less per litre. Dry wines are generally viewed as more sophisticated and healthier, but dessert wines and fortified wines such as ports have their place at special occasions and with certain food pairings.
According to South African laws, no sweeting agent may be added to wine prior to fermentation with the exception of the production of Cap Classique or sparkling wine. In this case, a triage (a mixture of sugar and yeast) is added to initiate the second fermentation and a dosage (mixture of wine, sugar syrup and S02 is added at the end of the process.
I hope that we have been able to shed some light into how ripening grapes at different stages affect the final wine and how much sugar your bottle of wine may have. Ultimately dry wine offers the healthier approach but a glass of port with some stinky cheese has always been a favourite.