A New and Simple Technique for the Direct Determination of the Equilibrium Relative Humidity of Foods

A LiCl-cell, developed for the measurement of the dewpoint of air (11), has been adopted for the estimation of the eqiiilibrium relative humidity of foods, the property which determines, within certain limits, the possibility of microbial spoilage.The products under investigation were contained in either a gauze basket (in the case of coarse, solid foods only) or in a set of parallel, shallow dishes, both coaxial with the LiCl-cell. Cell and containers were immersed in a closed metal vat, equipped with a thermostat-controlled water circulation device. In order to increase the rate of establishment of temperature equilibrium, the LiCl-cell was moreover equipped with a bifilar coil, in series with the water circulation through the wall of the vat.Values for equilibrium relative humidity obtained in this way for foods and for sodium chloride solutions correlated satisfactorily with the data derived from measurements according to classical techniques.Determinations according to the new method require considerably less time: one hour at the most, versus at least one day in other electric hygrometers (44) or several days by the older static methods (22).