The soybean, Glycine max, is a legume and a foundational crop in global agriculture, serving as a versatile source of protein and oil. Originating in East Asia, the plant’s seeds have become a staple ingredient worldwide due to their unique nutritional profile and adaptability. Understanding the different classifications is necessary given the variety of ways soybeans are cultivated, processed, and consumed.
Primary Classification by Color and Maturity
Soybeans are primarily categorized by the color of their mature seed coat and their harvest timing. The standard commodity type is the yellow soybean, which accounts for the vast majority of global production. These mature, dried beans are high in protein and oil, making them the primary source for industrial crushing and the base for many common soy-derived products.
The black soybean is a less common variety, featuring a dark seed coat. Black soybeans are traditionally favored in some East Asian cuisines and are used in certain fermented products, sometimes providing a distinct aesthetic in finished foods.
The third major type is the green soybean, known commercially as edamame, which is distinguished by its maturity. Edamame is harvested while the pods are still green and the beans are immature, soft, and sweet, intended for direct consumption as a vegetable. This early harvest prevents the full development of starches and oils, resulting in a different texture and flavor profile compared to their mature counterparts.
Culinary Forms and Derived Products
Most soybeans, primarily the mature yellow bean, undergo significant transformation into derived products that consumers encounter daily. Soy milk and tofu are common transformations, created by first soaking dried beans and grinding them with water to produce a slurry. This mixture is heated to deactivate anti-nutritional factors and filtered, separating the liquid soy milk from the fibrous pulp, known as okara.
Tofu production involves adding a coagulant, such as calcium sulfate or magnesium chloride, to the hot soy milk, causing the proteins to aggregate. This coagulation forms curds, similar to cheesemaking, which are then pressed to remove excess liquid and set into solid blocks of varying firmness. The addition of these salts during this stage often contributes to the final product’s mineral content.
The primary industrial use for soybeans is crushing, which separates the bean into its two main components: oil and meal. Soybeans typically contain between 18% and 20% oil, which is extracted by cracking and flaking the beans, often using a solvent like hexane for high-efficiency extraction. The crude oil is then refined, bleached, and deodorized for use in cooking oils, margarine, and various industrial applications.
The remaining material after oil extraction is soybean meal, a highly concentrated protein source accounting for about 80% of the crushed bean’s weight. This meal, containing roughly 45% to 50% protein, is primarily used as a protein supplement in livestock and poultry feed globally. A small fraction of the meal is further processed into soy flour, concentrates, and isolates for human food products.
A different category of products involves fermentation, which uses specific microorganisms to transform the bean’s structure and flavor. Miso, a savory paste, is created by fermenting cooked soybeans, often mixed with rice or barley, using a mold called Aspergillus oryzae (koji). Similarly, tempeh is made by inoculating cooked, dehulled soybeans with the fungus Rhizopus oligosporus, which binds the beans into a firm, white cake. Natto is produced by fermenting whole, cooked soybeans with the bacterium Bacillus subtilis natto, resulting in a product characterized by a sticky, stringy texture and a strong aroma.
Distinctions in Agricultural Cultivation
Soybeans are also distinguished by the methods used to grow them, which affect their market use and labeling. The majority of soybeans grown globally are genetically modified (GM), engineered primarily for herbicide tolerance. This trait allows farmers to apply broad-spectrum herbicides, such as glyphosate or dicamba, to control weeds without damaging the soybean crop itself.
In contrast, a smaller segment of the market focuses on non-GM and Identity Preserved (IP) soybeans, which are cultivated and handled with strict segregation measures. Identity Preservation is a system that ensures a specific trait, such as high protein content or non-GM status, is maintained from the farm through to the final processor. These IP soybeans often command a price premium and are used for specialty human foods like high-quality tofu and soy milk, particularly for export markets with strict non-GM import requirements.
The organic classification requires the use of non-GM seed and prohibits synthetic fertilizers and pesticides for at least three years before harvest. Organic cultivation relies on methods like crop rotation and mechanical cultivation for weed control. Organic soybeans are nearly always non-GM and are highly valued for the premium food-grade market, appealing to consumers who prioritize production methods and specific labeling.