Toward prediction of porosity in foods during drying: A brief review

Four generic trends of pore formation during drying are identified from the literature. The present prediction methods are mainly based on empirical c orrelations. It is common to correlate porosity with water content by quadr atic, polynomial, or exponential forms of equations, which do not provide i nsight into the physics of the process. The glass transition theory is one of the proposed concepts to explain the process of shrinkage and collapse d uring drying. However, the glass transition theory does not hold true for a ll products. Other concepts, such as surface tension, structure, environmen t pressure,and mechanisms of moisture transport also play important roles i n explaining the formation of pores. It is hypothesized that as capillary f orce is the main force responsible for collapse, so counterbalancing this f orce causes formation of pores and lower shrinkage.