Fishmeal is made by cooking, pressing, drying, and grinding of fish or fish waste to which no other matter has been added. It is a solid product from which most of the water is removed and some or all of the oil is removed. Four or five tonnes of fish are needed to manufacture one tonne of dry fishmeal. Of the several ways of making fishmeal from raw fish, the simplest is to let the fish dry out in the sun. This method is still used in some parts of the world where processing plants are not available, but the end product is poor quality in comparison with ones made by modern methods. Now, all industrial fish meal is made by the following processes: Cooking: A commercial cooker is a long, steam-jacketed cylinder through which the fish are moved by a screw conveyor. This is a critical stage in preparing the fishmeal, as incomplete cooking means the liquid from the fish cannot be pressed out satisfactorily and overcooking makes the material too soft for pressing. No drying occurs in the cooking stage. Pressing: A perforated tube with increasing pressure is used for this process. This stage involves removing some of the oil and water from the material and the solid is known as press cake. The water content in pressing is reduced from 70% to about 50% and oil is reduced to 4%. Drying: If the meal is under-dried, moulds or bacteria may grow. If it is over-dried, scorching may occur and this reduces the nutritional value of the meal. The two main types of dryers are: Direct: Very hot air at a temperature of 500 °C (932 °F) is passed over the material as it is tumbled rapidly in a cylindrical drum. This is the quicker method, but heat damage is much more likely if the process is not carefully controlled. Indirect: A cylinder containing steam-heated discs is used, which also tumbles the meal. Grinding: This last step in processing involves the breakdown of any lumps or particles of bone.