The stabilisation of preserves through the lowering of water activity (aw) and the reduction of pH value are studied as alternatives to the traditional pasteurising/sterilising treatments. aw of samples of pesto has been reduced using two binary systems of humectants: KCl–fructose and KCl–saccharose. The microbiological stability of samples was assessed through the inoculation of Clostridium perfringens spores. Moreover, pH values, aw and colour parameters were measured. The results have pointed out that aw reduction and controlled temperature of storage inhibited the development of C. perfringens. In particular, run 1 (aw 0.92 and temperature 25 °C) allowed a significant increase of the stability time of the samples. The reduction of aw may be a valid alternative to the traditional treatments of stabilisation in maintaining the organoleptic characteristics of the fresh product.