Automated impedance measurements were used to classify samples of frozen concentrated orange juice as acceptable (< IO4 CFU/ml) or unacceptable (72 IO4 CFUlml). Calibration curves relating initial microbial concentration to impedance detection time were generated for several orange juice isolates. Cut-off times of 10.2 hr for bacteria and 15.8 hr for yeasts were adopted. More than 96% of 468 retail samples were correctly classified using automated impedance measurements. This technique has several advantages over other automated systems, including lower cost and reduced demand for technician time, and it provides reliable results much quicker than does the agar plate count. Cultures MATERIALS & METHODSTwo bacterial species (Lactobacillus fructivorans, Leuconostoc mesenteroides) and two yeasts (Candida tropicalis, SaccharomJaces chevalieri) were used for preparation of calibration curves. Each was isolated from orange juice (OJ) and propagated by transfer every 3-5 days into sterile single strength OJ (I2"Brix) at 30°C. Impedance Measurements