3.3.3. Water activity and shelf life

3.3.3. Water activity and shelf life
  • Objective of dehydration is to remove water from the deepest part of the flesh quickly enough to reduce water activity below the minimum for microbial growth, before significant spoilage takes place.
  • Objective of salting is to ensure that the salt penetration is rapid enough to similarly lower the water activity in the deepest parts of the flesh.
On completion of the process, a saline equilibrium between the muscle and the surrounding salt solutions is achieved. The maximum concentration attainable is that which corresponds to a saturated brine solution (i.e. around 26%) under normal temperature conditions. Practically, concentrations would be lower than this due to the presence of other solutes in the fish cells. Salt fish, then, at least theoretically, would have the water activity of a saturated common salt solution, 0.75, notwithstanding the extent to which it has been dried during and after the salting process. However, salted fish reduced to ‘biscuit cure’ dryness in drying kilns, or in the open air at low humidity, can absorb a considerable amount of moisture before the 0.75 water activity is exceeded, thereby initiating microbial growth leading to spoilage.

Last modified: Friday, 13 July 2012, 4:52 AM