Black olive fermentation characteristics and diffusion of preservatives into olives were evaluated in brines containing 500ppm potassium sorbate, 1000ppm sodium benzoate, 500ppm sodium benzoate + 250ppm potassium sorbate and no preservative (control). Changes in brine pH, acidity and microbial population (lactic acid bacteria, yeasts, moulds) were followed during fermentation and storage. Results indicated that K-sorbate when used at 500ppm concentration in black olive fermentation had a slight stimulatory effect on the growth of lactic acid bacteria. The yeast counts of brines containing 500 ppm K-sorbate and 1000ppm Na-benzoate were lower than for the brine containing 250 ppm K-sorbate + 500ppm Na-benzoate and for the control with no preservative, while mould growth was completely inhibited in all treatments during fermentation. Mould counts stayed below the detection Limit (<10 cfu g(-1)) during 214 days of vacuum-packaged storage. Yeast counts showed a progressive decline within 28 days of storage and then stayed relatively constant in all treatments thereafter. The level of yeast population was higher in the control sample than in the sample containing both preservatives during storage. The diffusion of Na-benzoate and K-sorbate into the olives after equilibrium was 64% and 80% during fermentation respectively. (C) 1999 Society of Chemical Industry.