The soybean, Glycine max, is an annual legume native to East Asia, valued globally for its protein- and oil-rich seeds. The plant transforms from a bushy field crop to the small, often yellow, seed used in countless food products. Understanding this visual progression clarifies what the term “soybean” describes.
The Overall Soybean Plant Structure
The soybean plant is an erect, bushy annual that typically reaches 1.5 to 3 feet in height. The entire structure, including the stem and developing pods, is often covered in fine, brownish or grayish hairs, giving it a fuzzy texture. The species is characterized by trifoliolate leaves, where each leaf is composed of three leaflets.
The plant’s growth habit is stocky and branching, creating a dense canopy. Soybeans produce small, inconspicuous, self-pollinating flowers that are either white or pale purple-pink. These flowers develop into seed-bearing pods, signaling the reproductive stage. As the plant matures, the leaves drop off, and the stem and pods dry out, changing color from green to shades of brown or tan.
Description of the Pods and Seeds
The fruit of the soybean plant is a small, slightly curved pod that grows in clusters, typically containing two to four seeds. The exterior of the developing pod is covered in fine hairs, similar to the stem. Pods start green and plump but gradually dry and harden, changing color to a mature brown or tan as the seeds inside ripen.
The fully mature soybean seed is generally oval or kidney-shaped, comparable in size to a small pea, and features a hard, water-resistant outer hull. While commercial varieties are predominantly yellow or tan, soybeans can naturally be black, brown, or green, or feature bicolored coats. A small scar, the hilum, is visible on the seed coat, marking where the bean was attached to the pod. Hilum color varies by variety, appearing black, brown, buff, gray, or yellow.
Common Commercial Forms
Soybeans reach the consumer market in two primary visual forms: the mature dried seed and the immature fresh bean. The mature, dried soybean is the hard, typically pale yellow or tan seed used for processing into products like soy oil, tofu, and soy milk. Dried for storage, the seeds are hard, dense, and ready for industrial use.
The other common form is edamame, the young, immature soybean harvested before the pods have dried and hardened. Edamame pods are bright green, plump, and softer than mature pods. The beans inside are a vibrant green color, tender, and are often served still in the pod. This difference reflects the stage of maturity: the pale, hard, dry bean is the mature form, and the bright green, soft bean is the vegetable form.