Until recently, the shepherds of Sardinia carried out various archaic practices as part of their everyday rural lives. The practice of boiling milk in cork vessels was still widespread; these were warmed using smooth round stones heated on the fire and then immersed in the milk, replacing them as they cooled with other hot stones. This was the technique used to heat the milk to then curdle it to make cheese. The method dates back to the earliest prehistoric times of the pre-ceramic age, when humans had not yet recognized the potential of terracotta as a means of storage and to create crockery. The cork was freshly extracted from the tree and placed by the fire so that the bark softened. It was then spread out like a wooden board, removing the rough outer part by raking it with a stone. Having polished the bark, the cork would be moved back towards the fire and bent into a cylindrical shape so that the part which would have been attached to the trunk faced outwards, in order to prevent the tannic part of the cork from coming into contract with the smoothed part on the inside. Wooden pegs would then be used to connect the two sides and the base, which was also made of cork. As well as boiling milk, the cork vessels were also used when milking the sheep.