Overview

Natto is a traditional Japanese food made from whole soybeans fermented with Bacillus subtilis var. natto. It has a powerful ammonia-like smell, a strong savory flavor, and a distinctive sticky, stringy texture. Natto is rich in protein and probiotics and is most commonly eaten as a breakfast food in Japan.

Origin and history

The earliest written record of natto appears in a 1068 Japanese document, but the practice of fermenting soybeans with straw-borne Bacillus subtilis likely predates written history [1]. The traditional method involved wrapping steamed soybeans in rice straw, which naturally contains the natto bacteria, and leaving them to ferment in a warm place. By the Edo period (1603–1868), natto was a common food in eastern Japan, particularly in the Kanto region, while western Japan around Kyoto and Osaka showed less enthusiasm for it [1]. In feudal Japan, natto and miso provided vital protein and nutrition for a population with limited access to meat. Commercial production using pure starter cultures began in the early 20th century, and today the city of Mito in Ibaraki Prefecture is considered the natto capital of Japan [2].

Varieties and aliases

  • Itohiki natto (糸引き納豆): The standard stringy natto, made with whole soybeans. This is the most common type.
  • Hikiwari natto (挽き割り納豆): Made from crushed or split soybeans, which ferment faster and produce a milder flavor.
  • Mame natto (豆納豆): A less common whole-bean variety with a firmer texture.
  • Karakuchi natto (辛口納豆): A regional variety from Ibaraki with a stronger, more pungent flavor.
  • Shiokara natto (塩辛納豆): A salt-fermented natto from the Tohoku region, distinct from the standard type.

Culinary uses

Natto is most commonly eaten as a breakfast dish: it is stirred vigorously with chopsticks until stringy, then seasoned with soy sauce, karashi (Japanese mustard), and sometimes green onion, and served over hot rice. It can also be used in natto maki (sushi rolls), added to miso soup, or mixed with raw egg for a protein-rich meal. In the Kansai region, natto is sometimes fried as natto tempura. The fermentation process produces the enzyme nattokinase, which is studied for its fibrinolytic (blood-clot-dissolving) properties, though this is not a culinary consideration.

Cross-cuisine context

Natto has a direct analogue in Korean cuisine: cheonggukjang (청국장), a fast-fermented whole-soybean paste with a similarly sticky texture and pungent aroma. Cheonggukjang is fermented for only two to three days, traditionally on warm ondol floors, and is used as the base for cheonggukjang-jjigae, a hearty stew. The fermentation agent in both cases is Bacillus subtilis, though the specific strains and preparation methods differ. In Japan, natto is eaten as a whole-bean condiment; in Korea, cheonggukjang is typically mashed into a paste and cooked into a stew.

No direct analogue exists in Mexican cuisine. While Mexico has fermented soybean products such as tempeh (introduced via Asian diaspora), the short-duration, high-ammonia Bacillus fermentation of whole beans is not represented in the Mexican culinary tradition. The closest textural analogue might be the sticky, mucilaginous quality of cooked nopales (cactus paddles), but the flavor profile is entirely different.

Notes for cooks

  • Natto is sold in small polystyrene or paper cups with a packet of soy sauce and karashi. The quality is indicated by the length and elasticity of the strings when stirred; longer strings indicate better fermentation.
  • Store natto in the refrigerator and consume by the expiration date. Freezing is possible but will alter the texture.
  • For those who find the smell or texture challenging, mixing natto with chopped green onion, raw egg, or a small amount of sesame oil can mellow the flavor.