At the Domaine d’Esthine, Brigitte Pieau uses cold saponification, which guarantees a natural surgras soap. The mixture of donkey’s milk, vegetable oils, essential oils, and caustic soda is first heated to around 104°F (40°C). It is then mixed for a few minutes and the resulting paste is poured into moulds (photo). Saponification continues until the soap hardens. This technique allows all the properties of the oils and butter used to be preserved, but also provides great moisturising power with the glycerine that is naturally created during the process.