(a) The Wine is Inverted.—A levorotation shows that the sample contains cane sugar.
(b) The Wine is Fermented.—A dextrorotation shows that both levorotatory sugar and the unfermentable constituents of commercial dextrose are present.
If no change take place in either (a) or (b) in the rotation, it proves the absence of unfermented cane sugar, the unfermentable constituents of commercial dextrose and of levorotatory sugar.
(2) There is right rotation.—This may be caused by unfermented cane sugar, the unfermentable constituents of commercial dextrose or both.
(a) The sugar is inverted:
(a₁) It rotates to the left after inversion.—Unfermented cane sugar is present.
(a₂) It rotates more than 2°.3 to the right.—The unfermentable constituents of commercial dextrose are present.
(a₃) It rotates less than 2°.3 and more than 0°.9 to the right.—It is in this case treated as follows:
Two hundred and ten cubic centimeters of the sample are evaporated to a thin sirup with a few drops of a twenty per cent solution of potassium acetate. To the residue 200 cubic centimeters of ninety per cent alcohol are added with constant stirring. The alcoholic solution is filtered into a flask and the alcohol removed by distillation until about five cubic centimeters remain. The residue is mixed with washed bone-black, filtered into a graduated cylinder and washed until the filtrate amounts to thirty cubic centimeters. When the filtrate shows a dextrorotation of more than 1°.5, it indicates the presence of unfermentable constituents of commercial dextrose.
(3) There is left rotation.—The sample contains unfermented levorotatory sugar, derived either from the must or mash or from the inversion of added cane sugar. It may, however, also contain unfermented cane sugar and the unfermentable constituents of commercial dextrose.