Mung bean glass noodles

Mung bean glass noodles (fensi) are thin, clear noodles made from starch, including mung bean starch, rather than from cereal flour. The threads are translucent, hence the name 'glass'. Starch is the main substance: Longkou Fen Si contains over 75 % of it.

The best-documented example is Chinese Longkou Fen Si, which has protected geographical status (PGI). Its specification calls it a dry thread-like product made from green beans and peas. The beans are soaked 36–60 hours in cold water or 10–40 hours at 20–40 °C, crushed, the skins removed, and the starch is precipitated with a fermented acid steeping liquor. Starch and water are gelatinized with steam into a translucent paste, pressed through a filter into threads, cooled, folded and left 8–10 hours, then dried in the sun or with hot air. The finished thread is under 0.7 mm across, the product has over 75 % starch and under 15 % water, and after 45 minutes of boiling fewer than 10 % of the threads break.

The name Longkou Fen Si is tied to trade. According to the specification, in 1860 the Hongtai shop opened in Hong Kong to buy vermicelli from Zhaoyuan, shipped from the port of Longkou, with 'Longkou Fen Si' printed on the packs. Longkou port was opened to foreign trade in January 1914.

Similar Korean dangmyeon is made from sweet potato starch. So glass noodles are not always made from beans, and what sets them apart is the raw material, not the look.

Why it matters to you. 'Glass' does not mean 'from beans': Longkou Fen Si is made from beans and peas, dangmyeon from sweet potato. Read the ingredients. Starch noodles contain no cereal flour, so do not confuse them with rice vermicelli, which is made from rice.