Aqueous solutions of 24 small carbohydrates have been analysed by low-temperature differential scanning calorimetry (d.s.c.). The method, based on analogue derivative thermograms, measured two thermomechanical properties characteristic of each non-crystallizing solute: T′g, the sub-zero glass transition temperature of a maximally freeze-concentrated solution and W′g, the amount of unfrozen water (UFW) kinetically immobilized in the glass at T′g. For 84 low-molecular-weight polyhydroxy compounds (PHCs) analysed to date, T′g ranged from –85 °C for ethylene glycol to –13.5 °C for maltoheptaose, and increased monotonically with increasing Mw. T′g plotted vs.M–1w showed a linear correlation characteristic of an homologous family of glass-forming linear oligomers. W′g ranged from 1.9 g UFW g–1 for ethylene glycol to 0.2–0.3 g UFW g–1 for several sugars and polyols, including maltoheptaose, and decreased with increasing T′g, showing fair linear correlations for several series of homologous solutes. We describe here the use of T′g and W′g, as invariant physico-chemical properties of glass-forming solutions at sub-zero temperatures, to interpret thermomechanical behaviour of small-carbohydrate–water systems in non-equilibrium glassy and ‘rubbery’ states, define structure–activity relationships and explain and often predict functional behaviour of such PHCs in various applications.