The use of ultrasound or acoustics applied at a level below that which causes cavitation to control the energy balance between particles and the liquid phase in a metastable liquid. In a disclosed example 15% (w/v) solution of eicosane (99% pure) was made up in a Heptane/Toluene mixture (80/20 v/v), (both 99% pure) and sonicated. Also claimed is a process comprising de-tempering of chocolate malt during re-work by the application of acoustic power which melts the crystal nuclei produced in the tempering operation without heating the liquid oil suspending phase. Also claimed is the provision of a source of ultrasound in the tank, in the tank take-off chamber, or on the fuel delivery line close to the location of the feed of the fuel to a diesel engine or a heating boiler. Advantageously the use of ultrasound of a certain power and frequency can control the metastable state and can inhibit or promote nucleation and thereby control the width of the temperature band defining the metastable state for crystallisation from liquids.
