Multi-Stage Creep Effect in Consolidation of Tofu and Okara as Soft Colloids

Consolidation experiments were carried out on pre-consolidated cakes of tofu (soybean curd) and okara (soybean curd refuse), which were soft colloids, by using a compression-permeability (C-P) cell. The variations in the average consolidation ratio of the cake over time, which is a measure of the degree of consolidation, were evaluated on the basis of the data of cake thickness versus time. Both the traditional Terzaghi model and the Terzaghi–Voigt model failed to describe consolidation behaviors of tofu gel and okara cake. A new multi-stage creep model consisted of a number of Voigt elements connected in series has been developed in order to elucidate the complicated consolidation behaviors of tofu and okara. It was shown that the consolidation behaviors of tofu and okara were accurately described using the present model. The consolidation of tofu gel, which has a high water-holding ability, was slower than that of okara, and the fraction of creep consolidation, especially ternary consolidation was more pronounced in tofu than in okara. The model calculations accurately described the dependence of consolidation behavior on consolidation pressure and the type and concentration of coagulants. It was found that the adjustable fitting parameters of consolidation appearing in the model formula remained nearly unaffected by the consolidation pressure in the range investigated. The consolidation rate approached a minimum value in the case of the tofu gel with high firmness prepared with a MgCl2 concentration of 0.05 mol/l.