Ultrasound crystallization detection using

From the general point of view, ultrasound has advantages regarding the measurement of dairy product quality in that it may be implemented inline, non-invasively and even using non-contacting techniques such as laser excitation and detection (Mulet et al, 1999). Ultrasound can also be safe, hygienic and economic in implementation, all characteristics desirable for any technique for the measurement of food quality (Povey, 1997a). Moreover, it can reveal aspects of the quality of dairy products which are not measurable by current techniques. An example is the extraordinary capability of ultrasound to detect crystal nucleation (Povey et al., 2001 Hindle et al., 2002). 

Ultrasound is by far the most sensitive technique for detecting the initial stages of crystallization. Ultrasound velocity is very sensitive to the state of fat in a dairy emulsion (Figure 21.2) and can be used to follow changes in the amount of solid fat which occurs as the temperature changes. 

In 1880, Pierre Curie and his elder brother Jacques Curie found that crystals of Rochelle salt could generate electric potential between opposing surfaces when the crystals were compressed in certain directions (i.e., piezoelectricity) [1]. Two years later, they confirmed that the reverse effect could also occur when the crystals were subjected to an electric field. However, the phenomenon of piezoelectricity and its converse piezoelectric effect did not receive much attention until the World War I when it was demonstrated that quartz crystals could be used as transducers and receivers of ultrasound in water to detect the submarine. In 1921, Cady made the first quartz crystal resonator based on the X-cut crystals [2]. But, the X-cut crystals exhibited very high temperature sensitivity, so that they could... 

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