Tallow quality is graded into four categories based on color and the amount of free fatty acids in the finished product. Free fatty acids develop in the fat before rendering and are, therefore, used as an indicator of freshness. Tallow quality grades are categorized as edible, prime, inedible and stock feed. Edible and prime tallow can be consumed by humans, inedible is used in soap and stock feed is added to pig and chicken feed.
Wet rendering produces the purest tallow. Fat is heated in water to a temperature between 130 and 140 degrees Fahrenheit. During the wet rendering process, gravity separates the impurities from the fat, which settle into the water. Higher temperatures can be used but cause undesirable colors.
Dry rendering is done by heating fat directly and removing the solids with a centrifuge. Temperatures used in dry rendering can exceed 212 degrees Fahrenheit and cause permanent discoloration.
Tallow intended for human consumption or soap is bleached to remove undesirable tints of color. As wet rendering can decrease the stability of tallow, antioxidants are commonly added to make it firmer.
The purest level of tallow is sanctioned for human consumption. It is commonly used as frying oil, a shortening for baked goods and in margarine. Edible tallow must contain no more than 1% solid matter, such as muscles and bones, and no more than 2% water, which causes rancidity in higher percentiles. Sheep or bovines slaughtered for edible tallow must be in good health at the time of butchering.
When mixed with lye, tallow becomes soap. As white soap is desirable, the purity of soap tallow is measured primarily by color. Hues of tallow are influenced by the animal used (bovine or sheep) and how clean the fat was before heated. Blood will turn tallow brown, excessive heat during the rendering process makes it red and chlorophyll adds a green tint.
Tallow candles are made by repeatedly dipping a wick into melted tallow but letting the tallow dry between each dip. The finer the tallow, the cleaner the candle will burn and, therefore, the grade of tallow should not be lower than inedible. Beeswax is added if the tallow is soft or unstable.