You guessed it! RS is a measurement of the sweetness of a wine. Wine makers measure sugars in wine at harvest in Brix or Balling scales in the U.S., a measurement of soluble solids and specific gravity which roughly translates into 1 gram of sugar per 1 liter of liquid. In fermented wine, we refer to remaining sugars as Residual Sugars, or RS in weight to volume ratios, g/L. However, not all RS is perceptible sugars like glucose and fructose. Scales of wine sweetness vary from place of origin, but the US version is usually from dry to very sweet. Dry wines are wines under 2g/L of sugars, although many are much drier. Sweet wines can have up to 45 g/L of sugars! Off-dry wines are usually wines with slightly perceptible sugars in balance with acids.