Rendering vessel Decanter
Raw material 1
Rendering vessel Decanter
Meal to mill
Meal to mill
Tallow tries) include hydrolysis using proteolytic enzymes or ensiling (12).
Animal fats are composed of triglycerides—three fatty acids esterified to glycerol. Fat quality is measured by titer; free fatty acid (FFA); FAC color (standard set by the Fat Analysis Committee of the American Oil Chemists Society); bleach color; and moisture, insoluble impurities, and unsaponifiable matter (MIU). Other tests that can be specified include saponification number, iodine value, peroxide value, and smoke point.
The fatty acid chain length and degree of saturation of the carbon bonds affect the fat's hardness or melting point (titer); the longer the chain length and the more saturated the fatty acid, the higher the titer. Fats of different species of animals and from different sites in the body have different titers. Type of feed can affect the titer, but rendering method does not.
When fat molecules break down, free fatty acids are released, so FFA content, which is usually expressed as percentage of free oleic acid, indicates the degree of spoilage that has occurred. To minimize FFA values, poor-quality raw material should be segregated from good-quality material, and material should be processed promptly. If material cannot be processed promptly, the raw material should be kept whole (unbroken) as long as practicable, to minimize microbial and enzymic activity, and preserved by cooling, or by adding acid. Processing equipment and storage tanks should be kept clean.
The factors affecting the color of fats include: animal breed, feed, age, and condition; source of the raw material; and presence of contaminants (feces, gut contents, etc).
Fats can be almost white, yellow, or green (from contact with chlorophyll in digested plant material), or red or brown (from overheating or from contact with blood). Processing parameters during rendering (temperature, time) influence fat color. Some color components can be removed by bleaching with activated clay, and the color of the bleached sample read in a Lovibond tintometer. Fat bleachability indicates the temperature and handling conditions that the tallow has been subjected to; the cleaner the raw material and the lower the temperatures used, the lighter the bleach color.
The MIU value indicates fat purity. Moisture content should be as low as possible, because microbial and enzymic activity can hydrolyze fat at fat-water interfaces. Insoluble impurities such as protein fines, ground bone, manure, and so on that were not completely removed during processing may form colloidal fines that are not removed by settling or centrifuging. Trace amounts of copper, tin, and zinc can cause fat oxidation, and any polyethylene that has melted during rendering can adversely affect industrial processes that utilize fats. Unsaponifiable matter is fatty components such as cholesterol and gums that cannot be converted into soap by the use of alkali. Such matter reduces soap yields and affects catalyst efficiency. Unsaponifiable matter can also impart objectionable odors.
The saponification number indicates the average length of fatty acid chains, and the iodine number indicates the degree of unsaturation. These values can be used to identify types of fats and oils. The peroxide value indicates the degree of rancidity. Tallow that is not rancid and with good oxidative stability will have a low peroxide value. The smoke point is directly related to FFA and is the temperature to which the fat can be heated before it begins to smoke.
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