Summary Tests were made to determine the extent of spreading of a salt charge as it passed through a vacuum pasteurizer. All tests were conducted with the equipment operating on tap water at a flow rate of 4,010 ± 10 lb per hour. Spreading of the salt charge was detected by instantaneously measuring the conductivity of the liquid as it passed a downstream electrode. A high-speed motion picture camera operated at 64 frames per second simultaneously recorded ammeter, voltmeter, and electric timer readings on 16-mm film. The sensing electrodes were placed beneath the first chamber and immediately after the product removal pump of the second chamber of the ultrahigh-temperature unit. The salt charge was injected into the flow immediately before the steam injector. The time differential between the slowest and fastest particles was about 5 sec when the salt charge left the first chamber and it increased to 10.6 sec at the discharge side of the product removal pump of the second chamber.