By Yoshi | Japan Unveiled
I want to begin with honesty: natto is difficult.
Not difficult to make (though the specific production requires specific conditions). Not difficult to find in Japan (it is available in every supermarket, every convenience store, and in most areas it is sold by specific street vendors). Difficult, specifically, for people who have not grown up eating it — difficult in the way that the most polarising foods of any culture are difficult for the specific reason that they require adjustment on the part of the eater rather than accommodation on the part of the food.
Natto does not meet you halfway. It does not tone down its specific smell for your convenience, it does not smooth out its specific texture for your comfort, and it does not apologise for the specific threads that it produces when stirred and that will end up, inevitably, somewhere you did not intend them to end up. Natto is what it is, and you either find a way to appreciate it or you do not.
I have written briefly about natto in the fermentation article, in the context of Japan’s broader fermented food tradition. In this article, I want to go deeper — into what natto actually is, how it is produced, what it does to your body, what it tastes like to people who love it, and how to approach it if you are one of the people who have not managed to love it yet but are willing to try.
What Natto Is: The Specific Fermentation
Nattō (納豆) — fermented soybeans — is produced by the specific action of the bacterium Bacillus subtilis var. natto on cooked soybeans. This specific bacterial strain — which exists naturally in rice straw, which is the specific traditional substrate used to ferment natto before the development of the modern industrial production methods — produces a specific complex of enzymes and compounds that transform plain cooked soybeans into natto’s specific character.
The specific transformation: Bacillus subtilis natto produces specific proteases that break down the soybeans’ proteins into specific amino acids and shorter peptides, developing the specific umami depth and the specific sharp flavour notes of natto. It produces specific poly-gamma-glutamic acid — the specific biopolymer that is responsible for natto’s most immediately obvious characteristic, the specific sticky threads that form when natto is stirred or stretched. And it produces specific vitamin K2 (menaquinone-7) in unusually high concentrations — a nutritional characteristic whose specific health implications I will address later.
The production process: steamed soybeans are inoculated with a pure culture of Bacillus subtilis natto and packed into specific containers (historically rice straw bundles, now typically small polystyrene containers) for fermentation at approximately 40 degrees Celsius for approximately twenty-four hours. The specific fermentation temperature and the specific fermentation time are the primary control variables — too cool and the fermentation is insufficient; too warm and the specific unpleasant off-flavours of over-fermented natto develop.
The specific packaging: the specific small polystyrene container of natto — approximately 45 to 50 grams, sealed with a specific film lid, packed with specific natto-specific condiments (a small packet of soy sauce and a small packet of karashi mustard) in the specific refrigerator section of every Japanese food retail point — is one of the most specifically Japanese of all food packaging formats and one of the most widely recognised objects in the Japanese domestic food landscape.
The Specific Flavour: What Natto Actually Tastes Like
Describing natto’s flavour to someone who has not eaten it is one of the more challenging descriptive tasks in food writing, because natto’s specific flavour is unlike anything in most international food cultures and because the specific combination of smell, texture, and taste that defines the natto eating experience is not accurately captured by any single description.
The specific smell: the most immediately challenging dimension for the uninitiated. Natto’s specific aroma — produced by the fermentation’s specific volatile organic compounds, including ammonia, various esters, and various other fermentation products — is powerful, complex, and distinctly earthy in the specific way that highly fermented protein-rich foods can be earthy. The comparison that most people make: slightly similar to a strong blue cheese, but specifically different in ways that make the comparison only approximately accurate.
The specific texture: natto stirred in its container with chopsticks produces the specific threads — hikimono (引き物 — threads) or neba-neba (ねばねば — the Japanese descriptor for sticky or slimy) — that are one of natto’s most distinctive physical characteristics and the specific aspect that many first-time eaters find most challenging. The threads are harmless — they are the specific poly-gamma-glutamic acid polymer that the fermentation produces — but their specific visual character (long, white, cobweb-like threads extending from the stirred natto) requires a specific adjustment of expectation.
The specific taste: underneath the specific smell and the specific texture, natto has a specific flavour that people who love it describe as deep, savoury, nutty, and specifically fermented — the fermented quality that has the specific depth of a long-matured cheese, the specific bean quality of the soybeans’ rich protein content, and the specific slightly sharp note of the fermentation byproducts. With the specific soy sauce and the specific karashi mustard that the package provides, natto achieves a specific flavour combination that its enthusiasts find deeply satisfying and that its detractors find insufficient compensation for the other challenges.
The Regional Division: East vs. West
The most specifically Japan-internal fact about natto is the specific geographic division in its consumption: natto is essentially a food of eastern Japan (the Kanto region and the Tohoku region) and is significantly less consumed in western Japan (the Kansai region of Osaka, Kyoto, and Kobe).
The specific cultural geography: surveys consistently show that natto consumption in the Kanto region is approximately three to four times higher per capita than in the Kansai region. Kansai — particularly the specific food culture of Osaka and Kyoto — has historically been resistant to natto in ways that go beyond mere personal preference into a specific cultural identity statement. The Osaka food person who says they do not eat natto is partly making a specific statement about the difference between Osaka and Tokyo food culture.
The specific historical reasons: natto’s origin as a specifically eastern Japanese fermented food product — developed in the specific cold-climate conditions of the Kanto and Tohoku regions where the specific Bacillus subtilis fermentation could be reliably controlled — meant that its initial development and distribution were concentrated in eastern Japan. By the time refrigerated distribution made natto available throughout the country, the eastern Japanese eating habit had been established for centuries and the western Japanese non-eating habit was equally established.
The contemporary situation: refrigerated logistics mean that natto is now available throughout Japan, and national consumption has increased somewhat in recent decades. But the specific cultural identification of natto with eastern Japan and the specific cultural resistance to it in western Japan remain features of the Japanese food landscape.
The Nutrition: What the Science Actually Shows
Natto is one of the most nutritionally studied foods in Japan, and the specific scientific literature on its health implications is both substantial and genuinely interesting.
Vitamin K2 (MK-7). Natto contains approximately 870-1000 micrograms of vitamin K2 (specifically the MK-7 form) per 100 grams — the highest concentration of this specific vitamin form in any single food. The specific health relevance of MK-7: it has a specific long half-life in the body (approximately three days, compared to approximately two hours for the more common K1 form), enabling it to activate the specific proteins involved in calcium metabolism and bone formation more effectively.
The specific Japanese epidemiological findings: the geographic distribution of natto consumption in Japan partially correlates with geographic differences in hip fracture incidence — a finding that is consistent with the specific role of vitamin K2 in bone health, though it does not establish causation (multiple confounding factors make causation difficult to establish from geographic correlation alone).
Nattokinase. Natto contains a specific enzyme — nattokinase (produced by Bacillus subtilis natto and found only in natto, not in other fermented soybean products) — that demonstrates specific fibrinolytic activity in laboratory studies: it dissolves fibrin, a protein involved in blood clot formation. The specific clinical relevance of nattokinase is contested — the studies demonstrating fibrinolytic activity are primarily in vitro and in animal models, and the human clinical evidence is limited — but the specific enzyme’s uniqueness and the specific Japanese interest in its cardiovascular health implications have made it one of the most researched components of the natto complex.
Probiotic bacteria. The specific Bacillus subtilis natto bacteria present in natto survive the digestive process in meaningful numbers and have specific interactions with the intestinal microbiome that are the subject of ongoing research. The specific probiotic properties of natto are part of the broader Japanese fermented food health interest.
How to Eat Natto: A Practical Guide
For the international visitor who wants to approach natto without either the cultural familiarity that makes it automatic for eastern Japanese people or the specific cultural resistance that makes it off-limits for some western Japanese people, a specific practical approach is useful.
Start with the morning context. Natto is overwhelmingly a breakfast food in Japan — served over rice, with the specific soy sauce and mustard packets, alongside miso soup and grilled fish as part of the washoku breakfast. Eating natto in its natural context — as part of a specific breakfast sequence where it is one component among several — is significantly more accessible than eating it alone.
Stir it thoroughly. The specific instruction on most natto packages: stir at least fifty times before eating. The specific effect of thorough stirring: the poly-gamma-glutamic acid threads that cause anxiety when they appear as individual long threads become shorter, more numerous, and more thoroughly incorporated into the natto, producing a more uniformly sticky preparation that is easier to handle.
Use the mustard. The specific karashi mustard that comes with natto provides a specific sharp heat that does two things: it cuts through the specific richness of the natto and it provides a specific flavour intensity that focuses the eating experience in a direction other than the specific fermented quality that challenges new eaters.
Eat it with hot rice. The specific temperature of hot rice moderates the specific intensity of the natto’s flavour and smell, and the specific mild sweetness of good Japanese rice provides a specific balance to the natto’s savouriness. Cold natto eaten alone is significantly more challenging than hot-rice-and-natto eaten together.
Natto is an acquired taste. But it is specifically worth acquiring, not merely as a cultural experience but as a genuinely distinctive flavour that exists nowhere else in the food world. The specific combination of the fermented depth, the soybean richness, the specific soy-and-mustard seasoning, and the specific hot rice that softens and integrates everything is, for the people who love it, one of the most satisfying morning flavours available.
— Yoshi 🫘 Central Japan, 2026
Enjoyed this? You might also like: “Fermented Japan: Miso, Natto, and the Foods That Foreigners Fear” and “Japanese Breakfast vs. Western Breakfast: How One Country Has Two Completely Different Morning Meals” — both available on Japan Unveiled.
