Soybean meal is the most important protein source used to feed farm animals. It represents two-thirds of the total world output of protein feedstuffs, including all other major oil meals and fish meal. Its feeding value is unsurpassed by any other plant protein source and it is the standard to which other protein sources are compared.
Soybean meal is the by-product of the extraction of soybean oil. Several processes exist, resulting in different products. In the solvent extraction process, the soybeans are cracked, heated, flaked and the oil is extracted by solvent (usually hexane). The extracted flakes are then dried to eliminate the solvent, toasted and ground. The soybeans may have been dehulled prior to extraction, and the hulls may be added back at the end of the process. In the mechanical process, the soybeans are cracked, dried, heated and fed to a mechanical press, and the resulting flakes are dried and ground. There are many variations of these processes, notably treatments that improve the rumen by-pass protein value of the meal for ruminants, including combinations of heating, mechanical treatments and chemical treatments. The extracted flakes may be further refined into soybean flour and isolates that have specific feed and food applications.
Soybean meal is usually classified for marketing by its crude protein content or by the sum of protein + oil. There is two main categories, the “high-protein” soybean meal with 49-50% of protein + oil and 3% crude fiber, obtained from dehulled seeds, and the “low protein” meal, with 44-46% protein + oil and 6-7% crude fiber, that contain the hulls. In solvent-extracted soybean meals, oil content is typically lower than 2% while it exceeds 3% in mechanically-extracted meals.