Researchers from the University Ibn Zohr in Morocco and Le Havre in France have demonstrated a new technique that could make significant savings by reducing waste and simultaneously obtaining more consistent high quality cheese.

Most cheeses are made by coagulating milk by adding the enzyme rennet, which turns it from fluid to solid. The enzymes break down the main protein in milk, casein, then the curd aggregates and gels. Better quality cheeses are obtained by cutting the curd to expel the whey at a given amount of time after the clotting point. This also maximizes yield and minimizes waste, so an accurate determination of the coagulation time is very important for finding an ideal time for cutting the curd.

A number of different ways of finding the coagulation time of milk have been used in the past including electrical, thermal and optical systems. The method developed by the researchers in Morocco and France uses ultrasound - very high frequency sound waves, and is known as the ultrasonic pulse echo technique. This method investigates the coagulation of milk by finding the velocity of ultrasonic waves in the milky substance.

Ultrasound generally travels faster through solids than through liquids so the velocity of the ultrasonic waves increase as more solid forms. This velocity increases rapidly up to the clotting point, and then slows as the curd develops. Dr F Bakkali of the University of Ibn Zohr has shown that measuring the velocity of ultrasound gives a better indication of the clotting time than other ultrasonic methods, which rely on measuring how quickly the liquid-solid mixture absorbs the waves.

"This new method is particularly important to the food industry because it is non-invasive making it more hygienic", said Dr. Amghar of the University of Ibn Zohr.

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(Reference: Measurement Science and Technology Vol. 12, No 12, pp 2154-2159.)


[Contact: Dr. A Amghar, Alice Bows]

08-Nov-2001