Bitter melon is a tropical and subtropical vine of the family Cucurbitaceae, widely grown in Asia, Africa, and the Caribbean for its edible fruit. Its many varieties differ substantially in the shape and bitterness of the fruit.
Bitter melon originated from the South Indian state of Kerala and was introduced into China in the 14th century. It is widely used in the cuisines of East Asia, South Asia, and Southeast Asia.
This herbaceous, tendril-bearing vine grows up to 5 m (16 ft) in length. Each plant bears separate yellow male and female flowers. In the Northern Hemisphere, flowering occurs during June to July and fruiting during September to November.
The fruit has a distinct warty exterior and an oblong shape. It is hollow in cross-section, with a relatively thin layer of flesh surrounding a central seed cavity filled with large, flat seeds and pith. The fruit is most often eaten green, or as it is beginning to turn yellow. At this stage, the fruit’s flesh is crunchy and watery in texture, similar to cucumber, chayote or green bell pepper, but bitter. The skin is tender and edible. Seeds and pith appear white in unripe fruits; they are not intensely bitter and can be removed before cooking.
Some sources claim the flesh (rind) becomes somewhat tougher and more bitter with age, but other sources claim that at least for the common Chinese variety the skin does not change and bitterness decreases with age.
When the fruit is fully ripe, it turns orange and soft, and splits into segments which curl back to expose seeds covered in bright red pulp.
Bitter melon comes in a variety of shapes and sizes. The cultivar common in China is 20–30 cm (7.9–11.8 in) long, oblong with bluntly tapering ends and pale green in color, with a gently undulating, warty surface. The bitter melon more typical of India has a narrower shape with pointed ends, and a surface covered with jagged, triangular “teeth” and ridges. It is green to white in color. Some bear miniature fruit of only 6–10 cm (2.4–3.9 in) in length. These miniature fruit are popular in Bangladesh, India (common name ‘Karela’), Pakistan, Nepal and other countries in South Asia.