AbstractThe survival rates of two freeze‐dried strains, Lactococcus lactis var diacetylactis and Lactococcus lactis var lactis, were evaluated using the Accelerated Shelf Life Testing (ASLT) method. The strains were initially isolated from a brand of a Tunisian fermented milk product. Lactococcus cell survival observed at higher temperatures was used to extrapolate to shelf life at a lower storage temperature of 4 °C. The apparent kinetics of the survival rate loss were estimated and the effect of storage temperature was quantified by determining the inactivation energies for various samples. The work has shown an overall higher survival rate of the strain Lactococcus lactis var diacetylactis. An average half‐life of a strain maintained at 25 °C was equal to about 7 days as compared with about 43 days at 4 °C. The addition of lyoprotectants such glycerol, saccharose and calcium carbonate to the drying medium, improved the survival of such bacteria.© 2001 Society of Chemical Industry