Dependable data on bulk density, volumetric shrinkage due to water loss and porosity are needed to model processes such as drying, packaging and storing. Experimental data are presented for all three properties. It is possible to model the water-loss-based bulk shrinkage coefficient to obtain a predictive equation based on composition of the foodstuff. From this, a generalized correlation is obtained which predicts bulk shrinkage coefficient knowing only the initial moisture content of the food. Porosities for the foodstuffs considered can be predicted through suitable correlations, but there is no generalized equation spanning all foods.

Effect of concentration and temperature on thermophysical properties of clarified apple juice was studied. Density, viscosity, specific heat, and thermal conductivity were measured at different conditions, mnging from 20 to 90°C and 12 to 70"Brix. Experimental data were related to the corresponding properties of water and compared with the behavior of sugar solutions. The results obtained were used to derive mathematical models and correlations for predicting these properties as a function of both concentration and temperature.

A simple procedure has been implemented to measure porosity of apples as a function of moisture contents. The method has been applied to apples with change in moisture contents by conventional air drying. It is shown that the pores, which for biological reasons are open, i.e. connected to the outside, at the onset of dehydration, remain so until X = 1.5 g/g. As dehydration proceeds the pores are split into two families of pores: externally connected pores and locked-in bores. Both total and open pore porosity can be predicted from experimental correlations. Alternatively, the total porosity can be estimated from data on bulk volume shrinkage and the average composition of the tissue by means of equations presented. The interpretation of experimental data using this approach confirms that there is a significant change in the three-dimensional arrangement of the cellular tissue below X = 1.5 g/g. The two approaches lead to the conclusion that, probably due to cellular collapse, the open structure that characterizes the fresh foodstuff changes into a structure with locked-in pores. This fact may help to explain the slow and difficult re-hydration which characterizes air-dried foodstuffs. This hypothesis will be followed up in future work. The information developed should be of help in qualitative and quantitative modeling of processes involving moisture changes.