It is the mutarotation tests. Mutarotation is the adjustment in the optical turn in light of the adjustment in the balance between two anomers when the relating stereocenters interconvert. Cyclic sugars demonstrate mutarotation as α and β anomeric frames interconvert.
Mutarotation was found by French scientist Dubrunfaut in 1846 when he saw that the particular pivot of watery sugar arrangement changes with time
