Fig. 39. teat chopping machine vdth "crude oil motor" drive 

 in the feed-house of a large trout fishery. Left, a small 

 chopping machine for hand power. 



The cooking or stecuning of large sea fishes and bony meat of warm blooded animals 

 is often done only to ease the screv/ tuminc through the chopper. The bones are soften- 

 ed by steaming, and coarser bones can easily be removed. In cases where there is no good 

 reason for heating, cooking and steaming is only justified v/hen the food is no longer 

 fresh enough or Tihen the flesh of side animals is being fed. Slaughter house waste today 

 is largely ob tainable only in the cooked condition and after veterinary inspection and 

 through the mediation of "Utilization Associations for Slaughterhouse V.'aste", Unfortun- 

 ately a tv/o to three hour cooking is required for softening bones. The shorter the time, 

 the better it is. Unnecessary heating, cooking or steaming of f- odstuf f s is most certain- 

 ly to be avoided, because heating will not unlock the food substances or increase the 

 digestibility. On the contrary, the utilization value of crude protein is lowered in 

 heated meat. At the same time vitamins are destroj-ed, nutritive substances are leached 

 out, and by the decreasing of food volume the nutritive substances are concentrated. The 

 concentration acts very unfavorably on the digestive organs of trout. On the contrary, 

 the object must be to suppress too large a concentration of foodstuffs by the addition of 

 ballast substances. Finally, according to Schaeperclaus (1931), there is no danger v^iat- 

 soever, that the feeding of uncooked sea fish will cause the entry of the gyrodactilus 

 infection. Also the entry of other diseases by means of fresh sea fish is not to be 

 feared. If the food must be cooked, it is recommended to change off -Rlth fresh food. 



If heating of the fopd is to be done for any of the reasons given, that is, to 

 destroy putrefactive bacteria and their toxins, or to ease the preparation, then steam- 

 ing is to be preferred to cooking. Although steaming occurs in soae circumstances v/ith 

 somewhat higher temperatures, j'et the necessary heating time is shorter. The food can be 

 "dry cooked", and will not therefore be leached out. The fat, which is undesirable in 

 trout feeding, is separated off by steam and may be saved and sold to soap factories. 

 The salt in salty foods should be extensively removed by the steaming. 



For steamers a large variety of apparatus nay be used, especially hinged steamers 

 which are used in agriculture. Even better are special fish food steamers (Fig. ^0) 

 manufactured by Gotthardt and Kuhne, Lommatzach, Saxony. They consist of tv;o separated 

 parts: - a steam generator, which can also be used for heating and i.ot water appliance, 

 and the actual steam hoods. The steam is piped into the hoods. The hoods, built 

 similarly to a gas oven, contains removable sieves. The capacity varies according to 

 size of the apparatus, from 15 to AO pounds of fish food. 



135 



