The sweetness of a wine is defined by the level of residual sugar (or RS) in the fermentation process. Residual sugar is the measure of the amount of sugars that remain unfermented in the finished wine. Any wine with over 45 g/L would be considered sweet, though many of the great sweetwines have levels much higher than this. The finest sweetwines are made with grape varieties that keep their acidity even at very high ripeness levels, such as Riesling and Chenin Blanc. How sweet a wine will taste is also controlled by factors such as the alcohol levels, the amount of tannin present, and whether the wine is sparkling or not. In the United States the wine industry measures the sweetness of must and wine in degrees Brix. Degrees Brix (symbol °Bx) is a measurement of the dissolved sugar-to-water mass ratio of a liquid. It is measured with a saccharimeter that measures specific gravity of a liquid or more easily with a refractometer. A 25 °Bx solution is 25% (w/w), with 25 grams of sugar per 100 grams of solution.