When bones are boiled up in water gelatine is produced. It is a soluble protein which is then purified and is available in sheet or powdered form. It acts as a gelling agent and is used in making aspics and in setting jellies and mousses, both savoury and sweet. The powdered or granular form should be sprinkled onto a little water and left until it is spongy and then fully dissolved by applying a gentle heat. This can then be added to the mixture which is to be set. Leaf gelatine must first be soaked in a little water to soften it and then added to warm liquid and dissolved. A rough guide is tat one sachet of granules (11.7 g) should set around 500 ml (17 fl oz) water. One leaf of gelatine should set about 150 ml (5 fl oz or ¼ pt) of liquid. Pineapple and papaya contain enzymes which break down the activity of gelatine, so don't use them together.