This section is from the book "Alcohol, Its Production, Properties, Chemistry, And Industrial Applications", by Charles Simmonds. Also available from Amazon: Alcohol: Its Production, Properties, Chemistry, And Industrial Applications.
This datum may often give useful information. If the wine is dextrorotatory, cane-sugar is present, or added glucose, or both. If after inversion the wine becomes lævorotatory, cane-sugar is indicated; if it still remains dextrorotatory and the polarisation value is over 2.25°, the inference is that added glucose is probably present. Should the original wine be lævorotatory, inverted cane-sugar is indicated, or lævulose, or both; and if the lævorotation is increased on inversion, some unchanged cane-sugar was present. Finally, if the original wine gave no rotation, either all the sugar has been fermented out, or a compensating mixture of dextro- and lævo-rotatory sugars is present. In this case, if inversion produces a lævorotation, the inference is that cane-sugar was present, and therefore also lævulose or other lævorotatory sugar.