Elongational flow studies of set yogurt

Three series of prepared set yogurt samples were tested using squeezing flow viscometry. Samples were compressed using an Instron UTM at constant deformation rate. The first series containing added caseinates exhibited deformation behaviour of a gel. Firmness was dependent on caseinate concentration. The second series contained skimmed milk powder. Their behaviour was more that of a colloidal dispersion at low added powder content and of a gel at higher added amounts. The third series contained carrageenan salts. Their behaviour was that of a dispersion irrespective of the carrageenan concentration. The consistency of the samples examined was evaluated using plots of stress growth coefficients as function of biaxial strain rate. The results indicated that the technique could be used to distinguish changes in yogurt structure caused by the addition of various additives at various concentration levels, to milk to enhance yogurt consistency.