Multi-analytical approach for monitoring the freezing process of a milkshake based product

On or off-line controls of the freezing process, used to ensure the desired final quality of frozen dairy desserts, is an important task, especially for manufacturers who consider the standard of production as a primary goal. One of the products of interest in this context is the milkshake, a drink that contains ice crystals and a precise content of air. Herein, we used three different techniques, based on as many prototypes, to monitor and control the freezing process of a milkshake based product over a period of 1–29 h: an optical technique based on a digital microscope and image analysis, a rotational rheometer and a capacitive device. The optical technique characterized crystal growth and air content during freezing, and can be regarded as a reference method. The dimension of ice crystals and content of air bubbles showed a non-linear increase during preparation time. Correlations were high, with coefficients of determination up to 0.991. Parameters measured by other techniques, such as a rotational rheometer and a capacitive device, also showed good, logarithmic correlations with freezing time, with R^2 values up to 0.964. Correlations between the main freezing parameters and data obtained with the rotational and capacitive techniques appeared good (R^2 up to 0.983). Thus, these latter techniques might conceivably replace more complicated and expensive optical methods used to monitor the freezing process, especially when processing a product characterized by a constant composition.