Milk pasteurization, 19th century artwork. This is an industrial scale bain marie (water bath) used to heat milk in order to prevent microbial growth. Developed by the French chemist Louis Pasteur, this food preservation process is known as pasteurization. The food or liquid is heated to the required temperature (below boiling for milk) and then cooled rapidly. This reduces the number of microbes, but does not destroy them all. Engraving from 'Grands Hommes et Grands Faits de l'Industrie' (Great Men and Great Facts of Industry), published in France circa 1880.