UNIT 4 RENDERING AND POULTRY BY-PRODUCTS Structure 4.0 Objectives 4.1 Introduction 4.2 Rendering 4.2.1 Preparation of Carcass Meal 4.2.2 Continuous Low Temperature Dry Rendering 4.2.3 Rendering of Animal Fat 4.3 By-products Available in Poultry Industry 4.3.1 Feather Processing 4.3.2 Processing of Hatchery Waste, Inedible Eggs and Egg Shells 4.4 Let Us Sum Up 4.5 Key Words 4.6 Some Usehl Books 4.7 Answers to Check Your Progress 4.0 OBJECTIVES After reading this unit, you will be able to: explain what is rendering; state different types of rendering employed for converting animal by-products into value added meals; justifL the importance of animal fat; narrate the steps for preparation of technical fat; describe different poultry by-products; and state the procedure of feather meal production. 4.1 INTRODUCTION The process of converting dead animals or condemned meat into value added products like carcass meal is referred as rendering. Actually rendering in earlier days was referred to the process of recovery of fat from dead animals, but now- a-days, the definition also covers the production of carcass meal, meat meal and technical fat. You will be studying about the preparation of bone meal and blood meal in the next unit. By-products of poultry industry include everything from poultry fmor processing plant that may not be directly used as human food. Some of these are hatchery waste, feathers, blood, egg shell, offal, fat and manure. This unit will also deal with these poultry by-products. Originally rendering means the recovery of fat fiom animal materid by heating but with the advancement in the by-product industry, it embraces all the process leading to the conversion of slaughterhouse by-products into animal feeds, fats and fertilizers. 4.2.1 Preparation of Carcass Meal For the preparation of meat cum bone meal or carcass meal, the process used is the thermal treatment i.e., rendering or sterilization. There are two types of technologies for utilization of carcass; they are dry rendering and wet rendering. Continuous low temperature dry rendering is used for producing better quality fats. In case of large animals like cattle, buffaloes, there is a significant value of dead animals for their hide, hooves and horns and subsequent products such as meat meal, bone meal and tallow. After separation of hide, horns and hooves, the remaining parts of thi: carcass should be conveniently discarded and sometimes could be further processed. The carcass rendering plant handles feedstock devoid of hide. horn, hoof and rurnen contents. The material contains protein, fat and water in different proportions and rendering is a process to recover proteins and fat while eliminating water. If rendering is not done, the material gets putrefied. The yield of the final product meat meal, bone meal and tallow depends largely on the weight and level of nutrition of the animal. A) Wet rendering The wet rendering method involves the use of pressure batch cookers in which the pre-cut raw material is injected with live steam to a temperature of 140°C under pressure for 3-4 hours. After this time, the pressure is slowly reduced and the fat run out into a receiver and further purified by gravity or centrifugation to settle out the water and fines. The proteinaceous solids or greaves are emptied from the cooker, and the fat removed by pressure and solvent extraction. They are ;hen gro~dand dried. Bone meal preparation primarily involves the wet rendering process. B) Dry rendering The dry rendering process uses heat in the form of steam and water over a period of 1-2 hour at atmospheric pressure to drive out water indirectly fiom the fat in the cooker without loss of nutrients. Here no steam or hot water is allowed to pass into the cooking vessel, but the steam is allowed into the outer jacket only. Dry rendering yields 20 per cent more than the wet rendering process. Pre rendering operations: Raw materials originating on the killing floor should be processed with emphasis on speed and thorough cleaning, so that the end product of maximum value inay be obtained. The raw materials should be prepared properly before placing it into the cooker. Head, feet, condemned carcasses from the killing floor and bones from the boning department are reduced or crushed to small pieces by shredders. Bones also can be reduced in size in machines called "pre breakers". Intestines and other soft tissue coming fiom the killing floor are dirty with full of feed or manure and therefore must be opened and cleaned as well as reduced in size before charging into the cookers in inedible rendering. Table 4.1: Comparisons between Dry Rendering and Wet Rendering Rendering and Poultry - -- By-products Wet Rendering Dry Rendering I In wet rendering the material In dry rendering the material is is cooked in added water. cooked in its own water. Temperature applied is about 110 OC Temperature applied is about 130°C and pressure of 40 psi, for 60 minutes and pressure of 60 - 80 psi, for followed by drying for about 3-4 hours 3 - 4 hours. Better sterilization of ---lmaterial at higher Temperature. The cooker is of vertical type. The cooker is of horizontal type. The recovery of fat is better than dry The recovery of fat is not better than rendering. To produce good grade wet rendering. Tallow is dark tallow, viscera must be cut and coloured. More tallow is lost in dry washed. rendered meat. I Yield of carcass meal is less than dry Yield of carcass meal is more than rendering as 25 per cent of meat is wet rendering. lost in the gravy. Flow chart for dry rendering Carcass received -1 Removal of hide, horn and hoof, evisceration and removal of stomach and intestinal contents -1 Carcass divided into pieces (manually) -1 Reduce the size of the pieces to about 60 rnrn (mechanically) -1 Loading such pieces into dry renderer -1 Cooking at 60- 80 psi for 3 - 4 hours -1 Cooked material emptied into percolating tank -1 -1 Centrifuged Fat removed -1 -1 Fat settling tank Wet material pressed and moisture reduced and -1 then dry material is pulverized (powdered) -1 Technical fat Meat cum bone meal By-products Processing Table 4.2: Composition of Meat cum Bone Meal Plant Constituents Percentage (per cent) Crude Protein Min. 55 Crude Fat Max. 7 Calcium Min. 10 Phosphorous Min.5.O Clostridium spores, salmonella and E. coli Nil Moisture Max. 7 Pepsin digestibility 85 Some basic information on stock feed: Knowledge of composition of raw material is required to calculate the yield of meals to be expected from different offals. Meats may vary greatly in their composition depending upon the animals and also hmdifferent parts of the anjmals from which they are derived. Irrespective of the type of raw material used, the aim is to obtain a final product with an approximate composition of 85 per cent protein and minerals, 7 per cent fat and 7 per cent moisture. Any excess of moisture or fat leads to reduction in keeping quality and is undesirable. As stock feed is not made from one type of raw material, the proportion of each ingredient will influence the final yield. If only lungs, tripe, intestines containing very high percentake of water are used, a much smaller yield will be obtained. A commercial meal can only be prepared without removing fat when original fat level in the raw material do not exceed three and half per cent though we usually get higher percentages (more than 7 per cent) of fat in raw materials. Hence, to maintain the desired fat percentage, expulsion of fat is required. Besides, the inherent characters of the raw materials, the yield of the final product depends upon the following factors. They are as follows: a Type of rendering method used i.e., wet rendering (soluble and suspended materials is lost) or dry rendering (all the components are fully salvaged). Speed of processing. a Type of equipments used. Experience and skill of the operators, which contribute to the gain or loss in the final yield. In general, the conversion ratio of raw materials to dry meal is: a 3 : 1 in dry rendering process 4 : 1 in wet rendering process a 5 : 1 in blood meal preparation 20 ! I Commercial terms used for various products Rendering and Poultry By-products i Commercial markets accept a definite terminology for animal by-products. They include: I I i) Raw bone meal: Raw bone meal is a misleading term and is defined as the meal prepared from bones which have been cooked in open kettle without steam pressure and are therefore, sterilized and safe for use. The protein content is usually high, not less than 23 per cent (only a small quantity of ossein is removed). Average composition: Protein - 26 per cent Calcium - 23 per cent I Phosphorus - 11 per cent Fat - Acceptable level of fat. ii) Steamed bone meal: Bone meal prepared by applying steam pressure either by dry rendering process or wet rendering process. Steam removes much of the proteins and fat. Average composition: Protein 7 per cent Calcium - 32.5 per cent Phosphorus - 15 per cent iii) Bone ash: Bone ash is the ash obtained by burning the bones in open air with free access to air and contains 15.3 to 16.6 per cent phosphorus. iv) Meat meaVDigester tankagemeat scrape/Dry rendered tankage: It is the product obtained by wet or dry rendering of animal tissue and should contain not more than 10 per cent phosphoric acid i.e., 4.4 per cent phosphorus and not less than 55 per cent protein.