The invention provides a method of treating a food beverage or cosmetic to inhibit microbial or cellular growth comprising subjecting the substance to low frequency ultrasound under elevated gas pressure at between 10 and 100 bar more typically 20 and 500 bar. Also provided is an apparatus for treating a substance which is a food beverage or cosmetic to inhibit microbial or cellular growth in the food beverage or cosmetic comprising : (i) a substance inlet (ii) a pressurisation zone the pressurisation zone comprising a pressurising gas inlet and low frequency ultrasonic generator and (iii) a depressurisation zone.
