Miso is a salted paste made from fermented soybeans — and it is, without exaggeration, one of the most important ingredients in Japanese cooking. It forms the base of the soup served at virtually every traditional Japanese meal, seasons everything from marinades to dressings, and has been a cornerstone of the Japanese diet for well over a thousand years.
In this article, we're going to take a deep look at miso: what it is, how the different types compare, how it's traditionally made (including the extraordinary three-year process still used by heritage producers), what the research says about its health properties, and how you can start using it in your own kitchen.
What Is Miso?
Miso is a traditional Japanese fermented paste made from soybeans, salt, and a fermentation culture called kōji (麹). The type of kōji used — and the grain it's grown on — determines what kind of miso you get. There are three main types produced in Japan, plus a fourth category for blends. Rice-malt miso dominates at 82% of the market.
| Type (Japanese) | English Name | Key Ingredients | Market Share |
|---|---|---|---|
| 米味噌 (Kome-miso) | Rice-malt miso | Soybeans, rice-malt, salt | 82% |
| 麦味噌 (Mugi-miso) | Barley-malt miso | Soybeans, barley-malt, salt | 4% |
| 豆味噌 (Mame-miso) | Soybean-malt miso | Soybeans, soybean-malt, salt | 4% |
| 調合味噌 (Chōgō-miso) | Blended miso | Mixture of different types | 10% |
Rice-malt miso dominates the market at 82%, making it by far the most common variety you'll encounter both in Japan and in the UK. It's the type most people picture when they think of miso.
Source: Ishii Miso Co. Ltd informational display, Nagano Prefecture
How Is Miso Made?
Miso is made by combining cooked soybeans with salt and kōji (a mould culture grown on rice), then fermenting the mixture in wooden barrels. Mass production accounts for over 80% of output and takes weeks. Traditional methods ferment for up to three years, producing miso with noticeably deeper flavour and complexity.
One of the finest examples of traditional production comes from Ishii Miso Co. Ltd, established in 1868 in Nagano Prefecture (historically known as the Shinshū region). Their speciality is Shinshu San-nen Miso (信州三年味噌) — a miso fermented for a full three years.
The Three-Year Process
The traditional process involves four key stages, each recorded on tags attached to the fermentation barrels.
Stage 1 — Shikomi (仕込): Initial Preparation
The soybeans are cooked, combined with rice-malt kōji and salt, and packed into large traditional wooden barrels called kioke (木桶). These barrels are bound with braided bamboo hoops and covered with cloth lids weighted with stones. The fermentation begins.
Stage 2 — Tenchi-gaeshi (天地返し): The Turning
Several months into the process, the miso is turned — literally "heaven-earth return" — flipping the contents of the barrel to redistribute the fermenting paste. This ensures even fermentation throughout the batch.
Stage 3 — Ikae 1 (移替①): First Transfer
The miso is transferred to a new barrel. This serves three purposes: to mix the miso and ensure even fermentation, to encourage changes in the balance of microflora and stimulate microbial activity, and to discharge methane gas that builds up during fermentation.
Stage 4 — Ikae 2 (移替②): Second Transfer
The transfer is repeated a second time during the three-year cycle, for the same reasons.
To give a sense of the timescales involved: Batch No. 623 at Ishii Miso, made with Nagano Prefecture soybeans, was started on 23 February 2024. Its tenchi-gaeshi was performed on 5 September 2024, and the first transfer took place on 8 January 2025. Its second transfer isn't scheduled until 23 December 2025 — just under two years after the initial preparation.
Meanwhile, Batch No. 642 was started just weeks ago — 21 February 2026 — with all subsequent stages still pending. One batch nearing completion, the next just begun. That's the rhythm of traditional miso production.
Source: Barrel production tags, Batch No. 623 and Batch No. 642, Ishii Miso Co. Ltd
The Fermentation Vessels
Traditional miso fermentation uses large wooden barrels (kioke) bound with braided bamboo hoops. They're covered with cloth lids and weighted with stones — a method that has remained essentially unchanged for generations. The kioke are a defining feature of traditional production — and their continued use at producers like Ishii Miso is part of what distinguishes the craft method from industrial processes.
What Are the Key Ingredients in Miso?
Miso is made from three core ingredients: soybeans, which provide protein; kōji (麹), a mould culture grown on rice that produces the enzymes driving fermentation; and salt, which makes up around 12% of the finished paste. The interplay between these components over months or years creates miso's distinctive umami flavour.
Soybeans (大豆)
Soybeans provide the protein backbone of miso. In Japan, soybeans have a particular historical significance: for much of Japanese history, a carnivore ban (肉食禁止令) meant that soybean-based products and fish were the primary sources of protein in the Japanese diet. This is the cultural context in which miso, tofu, soy sauce, and nattō all became essential rather than optional.
Rice-Malt Kōji (麹)
Kōji is the engine of fermentation. It's a mould culture grown on rice (for rice-malt miso), and it produces the enzymes that break down the soybeans during the long fermentation period.
| Enzyme | Function |
|---|---|
| Protease | Breaks down protein |
| Amylase | Breaks down starch |
| Lipase | Breaks down fat |
These enzymes work alongside yeast and lactic acid bacteria, which develop during fermentation and contribute to miso's complex flavour profile. The interplay between these microorganisms over months or years is what gives traditionally fermented miso its depth — something that rapid mass production cannot fully replicate.
Source: Ishii Miso Co. Ltd manufacturing information panels
Salt
Salt content in miso sits at around 12%. It serves a dual purpose: seasoning and preservation. A common concern is that miso must therefore be very high in sodium, but context matters. A traditional Japanese meal of rice and miso soup contains approximately 2.0g of salt total (rice contributing 0.8g, miso soup 1.2g), compared with 1.2g for a bread-and-side-dishes meal. The difference is smaller than many people assume.
Source: Salt intake comparison display, Ishii Miso Co. Ltd
Popular Products
[Insert SushiSushi miso products here — white miso, red miso, awase miso, etc. with product images and VIEW PRODUCT links following the same format as the Shio Koji post]
Health Properties of Miso
Research suggests miso may offer several health benefits, including associations with reduced rates of certain cancers and lower blood pressure. However, findings should be read as indicative rather than conclusive.
Research into the health properties of miso is ongoing, and the body of evidence is substantial and growing. That said, no single food should be treated as a medical intervention.
Functional Properties
Japanese research has investigated miso across a broad range of potential health applications. A poster published by the Miso Health Committee (みそ健康づくり委員会) lists the following functional properties attributed to miso: cancer prevention, anti-ageing effects, cholesterol control, gastric ulcer prevention, removal of radioactive substances, digestive promotion, and skin health benefits.
Research Highlights
Gastric cancer: A 1982 study by Hirayama (published in Nutrition and Cancer, 3, 223–233) examined mortality rates from gastric cancer against frequency of miso soup consumption. The data suggested an inverse correlation — higher miso soup consumption was associated with lower gastric cancer mortality rates.
Breast cancer: Separate research found that frequent miso soup consumption was associated with a reduced relative risk of breast cancer. This finding was part of the JPHC (Japan Public Health Centre-based Prospective) Study, a large multi-purpose cohort study conducted across multiple centres in Japan.
Blood pressure: Research displayed at the Ishii Miso factory compared blood pressure readings with miso extracts at two concentrations (1.5g/cup and 0.75g/cup) against a control group. The data suggested miso extract may help reduce blood pressure in those with high blood pressure.
It's worth noting that these are primarily Japanese studies, often displayed as part of industry-supported educational materials. The research is legitimate and published, but as with all nutritional science, individual results will vary.
Sources: Hirayama, T. (1982) Nutr. Cancer, 3, 223–233; JPHC Cohort Study; Miso Health Committee (みそ健康づくり委員会) poster; research display panels, Ishii Miso Co. Ltd
A Brief History of Miso
Miso has been part of the Japanese diet for over 1,300 years, first documented in the 7th century as a provision for military rations. Its high protein content and long shelf life made it essential in a culture where a carnivore ban restricted meat consumption for much of history.
7th century — Miso is first documented as a provision for military rations. Its high protein content, long shelf life, and portability made it ideal for armies on the move.
12th century — Miso soup enters the samurai diet, becoming a regular part of the warrior class's daily meals.
15th–16th century — During the warring states period, miso becomes widely consumed across all levels of Japanese society. Its importance as a source of protein is reinforced by the ongoing carnivore ban, which continued to restrict meat consumption.
From those military origins to its position as a daily staple, miso has been quietly essential to Japanese life — and producers like Ishii Miso, now in their second century of operation, maintain the traditional methods that have defined the craft since long before industrial production existed.
Source: Historical display, Ishii Miso Co. Ltd, Nagano Prefecture
How to Use Miso
Miso is most commonly used to make miso soup (misoshiru), but it works equally well as a marinade for fish and meat, stirred into dressings and sauces, or dissolved into stews and braises for umami depth. Add miso towards the end of cooking to preserve its living cultures.
Beyond soup, miso works brilliantly as a marinade for fish and meat, stirred into dressings and sauces, spread on grilled aubergine (the classic nasu dengaku), or dissolved into stews and braises for depth of flavour. A general rule: add miso at the end of cooking rather than the beginning. Prolonged boiling can damage the living cultures produced during fermentation.
White (shiro) miso is milder and sweeter — good for dressings, light soups, and delicate fish. Red (aka) miso is stronger and more savoury — better for heartier dishes, marinades, and robust soups. If in doubt, start with a blended (awase) miso, which balances the two.
Frequently Asked Questions
What does miso taste like?
Miso has a deep, savoury umami flavour — salty with complex undertones that develop during fermentation. White (shiro) miso is milder and slightly sweet, while red (aka) miso is stronger and more intensely savoury. The longer miso ferments, the deeper and more complex its flavour becomes. A three-year aged miso will taste markedly different from one made in weeks.
Is miso vegan?
Traditional miso paste is vegan. The three core ingredients are soybeans, kōji (a fermentation culture grown on grain), and salt — no animal products. However, always check the label on commercial products, as some may contain additional ingredients beyond the traditional three.
How should I store miso?
Store miso in the fridge once opened. It keeps well for months — the high salt content acts as a natural preservative. You may notice the colour darkens slightly over time; this is normal and doesn't affect quality. Keep the lid tightly sealed to prevent it from drying out.
What is the difference between white miso and red miso?
White miso (shiro miso) ferments for a shorter period, resulting in a milder, sweeter paste suited to dressings, light soups, and delicate dishes. Red miso (aka miso) ferments longer, producing a stronger, more savoury flavour better suited to hearty soups, marinades, and robust dishes. Blended (awase) miso combines both.
Is miso high in salt?
Miso contains around 12% salt, but context matters. A serving of miso soup contains approximately 1.2g of salt — roughly the same as the side dishes in a bread-based meal. A full traditional Japanese meal of rice and miso soup totals about 2.0g of salt. Used in normal quantities, miso's sodium contribution is moderate.
Where to Buy Miso in the UK
If you're looking for high-quality miso paste to buy in the UK, our online store stocks a range of authentic Japanese miso — from white and red to specialist long-fermented varieties — all available with fast delivery across the UK.
Technical data sourced from Ishii Miso Co. Ltd, Nagano Prefecture, Japan. Established 1868. All factual claims in this article are drawn from factory display panels, production records, and published research cited at the Ishii Miso facility.
