Effects of seasonal variations on the quality of set yogurt, stirred yogurt, and Greek-style yogurt.

We studied the effects of seasonal variations on the quality of stirred yogurt, set yogurt, and Greek-style yogurt over 2 milking seasons in New Zealand. Correlations between the properties of the yogurts, the characteristics of the milk, and the acid gelation properties induced by glucono-δ-lactone, reported in our previous works, were also explored. Set yogurt and Greek-style yogurt from the early season had the highest firmness over the seasons. The yogurt firmness correlated with the gel strength of glucono-δ-lactone-induced acid gels, indicating that the latter could, to some extent, predict the seasonal variations in the firmness of set yogurt. The correlation studies highlighted the potentially important role of the glycosylation of κ-casein in the seasonal variations in the yogurt structures. Yogurt made from mid-season milk had the lowest water-holding capacity, which may have played a part in lowering its firmness and viscosity. Late-season stirred yogurt displayed the strongest resistance to shear-induced thinning, which might arise from the unique viscoelastic properties of late-season yogurt gels.