Nibs contain ca. 55% cocoa butter, which exists in solid form within the cells. Grinding ruptures the cell walls releasing the cocoa butter, while at the same time frictional and/or applied heat raises the temperature above 34 C, the melting point of cocoa butter. The particle size of the non-fat portion is progressively reduced and a fluid mass the cocoa liquor is produced. This consists of solid particles in suspension in a continuous fatty phase. Grinding may be carried out by several different types of equip-ment. Until fairly recently, all were evolutionary developments of the original stone mills, which used sets of horizontal disks Nib or partly ground liquor was fed to the centre of the stones and ground during movement towards the periphery. Efficient grinding necessitated the cutting of grooves in the surface of the stone disks, which required frequent refacing. The process also gener ated a considerable amount of heat, which resulted in strong flavours in the cocoa liquor. Stone disks were gradually replaced by grooved metal disks. Early liquor mills of this type had vertically mounted grinding discs, but more modern designs have readopted a horizontal configuration. The most common type employs three sets of grinding discs, the nibs being ground in three stages. Mills are constructed to provide very accurate setting and a very fine liquor can be produced. The mills are cooled to prevent liquor overheating