A method where a continuous flow of an oil-in-water emulsion is fed to a cavitator (10), the oil-in-water emulsion is tempered and then reversed or broken in the cavitator (10) and a continuous flow of water-in-oil emulsion or broken oil-in-water emulsion is discharged out of the cavitator (10). The oil-in-water emulsion can contain water, milk, cream, and/or recombined liquids. The reversed emulsion can be a low-fat butter or a low-fat margarine. The broken oil-in-water emulation can leave the cavitator as butter fat and butter milk. Use of cavitation or of a cavitator (10) to reverse or break an oil-in-water emulsion. An apparatus (1) with a feed pump (5) and a cavitator (10), a first heat exchanger (7) for tempering a flow of an oil-in-water emulsion pumped by the feed pump (5) to the cavitator (10) and a second heat exchanger (15) for cooling a water-in-oil emulsion or for cooling a broken oil-in-water emulsion that is pumped from the cavitator (10) through the second heat exchanger (15).
