Fresh pineapple, it turns out, cannot be used to make gelatine. Gelatine powder is rich in proteins and cellulose, and when mixed with hot water, it forms protein particles that aid the gelling process, resulting in a gelatine dessert. However, fresh pineapple contains an enzyme called bromelain, which breaks down the structure of proteins. As a result, gelatine cannot set when fresh pineapple is added to it.