Baumé

Baumé – French unit for measuring the amount of sugar in the must.
This is measured through the use of a baumé- indicator, a sort of thermometer which is placed in the must.
 A refractometer is also used, which determines the refractive index of the light in a single drop of liquid, thus indicating the level of sugar.

Nowadays when determining the ripeness of the grape the fenolic ripeness is used: the ripeness of the tannins and colour.
This can be determined through study of the grape seed.