Oechsle scale The mass difference between equivalent volumes of must and water is almost entirely due to the dissolved sugar in the must. Since the alcohol in wine is produced by fermentation of the sugar, the Oechsle scale is used to predict the maximal possible alcohol content of the finished wine. This measure is commonly used to select when to harvest grapes. In the vineyard, the must density is usually measured by using a refractometer by crushing a few grapes between the fingers and letting the must drip onto the glass prism of the refractometer. In countries using the Oechsle scale, the
Wine Grapes franc may have originated in Basque country of Spain. Additionally the origins of the assumed to be French varieties of Mourvèdre, Grenache and Carignan are shown to likely be Spanish instead. Another detail revealed by DNA testing and reported in "Wine Grapes" is that several northern Italian white wine grape varieties including Favorita, Pigato and Vermentino are genetically the same grape vine which is known under the synonym of "Rolle" in France but has no genetic relationship to the Rollo grape of Liguria. A number of grape varieties are illustrated by reproductions of colour plates from "Ampélographie. Traité général de