A modern bain-marie
A balneum Mariae, also known by its modern name bain-marie, is a double-boiler (cooker) originally used in alchemy. Alchemists used the device to gently heat materials for prolonged periods of time. This was supposed to simulate the conditions thought to exist deep underground where precious metals were formed.
Invention of the balneum Marie is attributed to Mary the Jewess, an ancient alchemist living in the third century A.D.The original term balneum Mariae was derived from the Latin words balineum (bath) and Mariae (Mary).
The balneum Mariae usually consists of two vessels. One is filled with liquid (usually water), the other contains the substance which needs to be heated and is positioned just above the liquid in the lower vessel. The maximum temperature can be changed by using different liquids.
In modern times the bain-marie is used in a variety of culinary tasks, including melting chocolates, making custards, milk sweets and cheesecakes. It provides a healthy and hygienic way of boiling and heating with a very even, stable temperature.
Interestingly, the bain-marie also survives in modern chemistry, finding uses in such areas as the pharmaceutical industry.
1. Chemical History Tour, Picturing Chemistry from Alchemy to Modern Molecular Science Adele Droblas Greenberg Wiley-Interscience 2000 ISBN 0-471-35408-2. Some sources equate Mary the Jewess with Miriam (sister of Moses) or to Mary Magdalene.