Natto (and why it's polarizing)

What it is

Whole soybeans fermented into a sticky, stringy, pungent mass — one of the most divisive foods on earth, beloved in eastern Japan and bewildering to many outsiders.

How it's made

Cooked soybeans are inoculated with ***Bacillus subtilis var. natto*** and fermented warm for about a day, during which the bacteria produce the slime and aroma.

Flavor profile & the science of why it's polarizing — Natto's challenge is threefold: (1) the stickiness/stringiness comes from polyglutamic acid (a glutamate polymer) plus fructan, producing those famous mucilaginous threads; (2) the pungent, ammoniacal, savory aroma comes from fermentation byproducts as proteins break down; (3) the soft, sticky texture is unlike anything in Western food. To fans it's deeply umami and nutty; to others the slime and smell are the barrier. The glutamate that makes it stringy is the same compound that makes it taste savory.

Culinary uses

Eaten over hot rice, stirred vigorously with karashi mustard, soy sauce, and scallion; in maki, with egg, in miso soup. A breakfast staple in the Kantō/Mito region.

Regional variations

Bean size varies (small-bean, large-bean, hikiwari crushed natto); Mito in Ibaraki is the legendary natto capital.

Cultural & historical context

A traditional health food celebrated for nattokinase and probiotics; its strong east-Japan regional identity (less loved in the west) makes it a cultural fault line within Japan itself.

Reference notes

Tags: `soy`, `fermented`, `bacillus`, `polarizing`, `japanese`. Related: tempeh, miso, sufu. Cuisine: Japanese (Kantō). Links → Bacillus subtilis, Umami, Karashi.