CONTINUOUS MEASUREMENT OF SURFACE-WATER ACTIVITY IN DRY SAUSAGE

During bacterial fermentation (souring, aromatization) dry sausage that is ripened for a long time is subject at the same time to a drying process during which the moisture content of the sausage is reduced as evenly as possible. Dry sausages are ripened in conditioning/smoking plant or in conditioned storage rooms and this is true of both industrial production and of small-scale production. In practice ripening is usually controlled by taking random samples. The sausages are sensorily evaluated for colour and appearance and for consistency of sausages and casings as well as for odour and flavour, but objective parameters such as weight loss, moisture content, pH and water activity (a(w)) are increasingly being taken into account. The microbiological and physical changes that take place during fermentation can, however, only be considered schematically and step-by-step, given the control based on time which has been applied hitherto. Ripening faults therefore often arise because of the different qualitative and quantitative composition of the meat products. We therefore sought for ways of determining surface water activity in the sausages continuously. Our aim was to develop a method that would not be sensitive to disturbances and that would also serve as a basis for the control of ripening plant (giving the theoretical value for relative air humidity). It was found that it was possible, on the basis of given thermodynamic laws, to determine the surface water activity of the dry sausages during ripening continuously, taking into account the sausage temperature, the air temperature and the relative humidity in the ripening chamber. The method we suggest is very simple, as only temperatures have to be determined. It is suitable for the continuous control of ripening processes in existing air-conditioning plant and also for use as a basis of control in micro-processor-controlled plant.