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 correlations. It is common to correlate porosity with water content by quadratic, polynomial, or exponential forms of equations, which do not provide insight into the physics of the process. The glass transition theory is one of the proposed concepts to explain the process of shrinkage and collapse during drying. However, the glass transition theory does not hold true for all products. Other concepts, such as surface tension, structure, environment pressure, and mechanisms of moisture transport also play important roles in explaining the formation of pores. It is hypothesized that as capillary force is the main force responsible for collapse, so counterbalancing this force causes formation of pores and lower shrinkage.