Residual Sugars are sugars that are still present in beer after the fermentation process is complete. A beer with a lot of residual sugar will have a fuller body and often taste sweeter, whereas one with less residual sugar will be drier and have a lighter mouthfeel. The sugars present in beer are generally derived from malted barley. Sometimes brewers will use adjuncts, different malted grains, corn, rice, syrup, honey, molasses, or other forms of sugar, in varying quantities, to complement the sugars extracted from the barley. The majority of these sugars are then consumed by yeast during the fermentation process.
Unlike winemakers, brewers rarely stop fermentations to produce a beer with higher residual sugar. Brewers, however, have far more control over the actual sugar profile and can control the amount of residual sugar in a number of ways. They can, for example, use sugars that they know the yeast will not be able to consume. Lactose, for example, is a nonfermentable sugar that is used in brewing milk stouts, also known as sweet stouts. Brewers can also manage the amount of sugar that will be left behind in a beer at various stages of the brewing process. During the mash, as the starches from the barley are being converted into sugar, the brewer can adjust the conditions to influence how many of the resulting sugars will be fermentable. Higher saccharification temperatures, for example, will result in the production of larger dextrins, which yeasts will not ferment. These dextrins will be left in the finished beer to contribute body and possibly sweetness. Brewers can also influence the amount of sugar that is consumed during fermentation by selecting yeast strains that will consume more or less of certain sugars. Yeasts that consume a lot of sugar are referred to as highly attenuative yeasts. The range of residual sugar in various beer styles is quite wide, with the driest well under 1% residual sugar by weight (lambics, some saisons, and other Belgian specialty styles) and some hefty barley wines nearing a syrupy 10% residual sugar. It is important to note, however, that not all sugars actually taste sweet and that the perception of sweetness is based upon a number of factors including temperature, carbonation, and bitterness. Beers with high residual sugars rarely taste as sweet as the sweetest wines. That said, at the dinner table, many beers possess enough residual sugar to make equally good (or excellent) accompaniments to a wide range of desserts and to be very pleasant digestifs.