The winemaker can determine the sweetness of a wine but it is a factor that is determined in the vineyard. As grapes grow and ripen they accumulate sugars, which is what reacts with the yeasts in the fermentation process in order to start fermentation. The fair majority of white wines and almost all red wines are made dry – which are made when a winemaker has ‘fermented to dry’.
Residual sugar (another very common term) refers to the amount of sugar that is left in a wine after fermentation. As a dry wine has used up all the fermentable sugars it is said to have been ‘fermented till dry’. Where many other wines are sweet, or have some degree of sweetness, due to their varying levels of residual sugar.
When tasting a wine that has residual sugar higher than the dry category you will be able to detect it on our tongue. Sweetness is, arguably, best detected at the tip of your tongue. You shall also be able to tell if it is of higher sugar content, as it will appear thicker in viscosity and taste sweeter.
Dry – The majority of wine that we drink falls into this category. Technically it is allowed to have up to 4 grams of residual sugar per litre. When tasting a dry wine it should have feel dry and refreshing.
Off-Dry – There are a few grape white grape varietals that often showcase more complex aromas/flavours when made in an off-dry style e.g. Pinot Gris or Gewurztraminer. These wines are legally allowed up to 9 grams of residual sugar per litre. When tasting an off-dry wine it should feel fuller in body and the acidity/tannins should be less obvious.
There is an exception with wines with incredibly high acidity, which shall make you perceive the sugar level as dry. This is due to the acidity level acting as a drying agent in this case. Many cheap white wines will often fall into this category but will have added acidity in attempt to balance them out and make them appear drier/more refreshing.
Medium-Dry/Medium-Sweet – These are wines that have a high enough level of sugar to overpower the drying effect of acidity or tannins, so are recognisably sweet on the palate. As well as be perceived as sweet they shall also have a fuller body and the aromas shall seem sweeter. You could compare this level of sweetness in a liquid with a 40/60 mix of golden syrup with water. These wines are allowed to have between 10-45 grams of residual sugar per litre.
Sweet – These wines are the classic sweet wines or dessert wines. They shall be a lot fuller in body and perceptively sweeter still. They shall be made from grapes that have gone through one of the numerous sweet winemaking processes (Botrytis, Late Harvest, Ice Wine or Passillerage). These wines must have at least 45 grams of residual sugar per litre but often will have closer to 75-120 grams.
The best sweet wines are those that have naturally high acidities as to balance out the high sugar levels. This balance is important otherwise it would be like drinking pure golden syrup – which appears flabby and not very appealing.