Miso

A fermented Japanese paste of soya beans, salt and koji, often with rice or barley. 1 tsp adds lots of umami. Very salty; barley miso (mugi) contains gluten.

What is miso? Centuries of umami

In the West, most of us know miso as the cloudy soup served before sushi at the restaurant round the corner. In Japan, though, miso is a respected, complex seasoning paste and the backbone of traditional Japanese cooking. To make authentic miso, steamed soya beans (sometimes also rice or barley) are inoculated with the noble mould Aspergillus oryzae (known as koji), salted generously and then fermented under heavy weights in cedarwood barrels in cool cellars – sometimes for up to three or four years. The longer the fermentation, the darker, stronger and saltier the paste becomes.

Light vs dark miso

There are countless regional types of miso, which fall into three main groups:

• Shiro miso (white miso): Fermented briefly (often just a few weeks), mild and slightly sweet – great for light dressings and pale soups. A large share of white rice forms the base.
• Aka miso (red/dark miso): Fermented for a long time (1-3 years), salty, intensely earthy and full of umami. Ideal for rich stews and robust Asian sauces. Here soya beans dominate.
• Awase miso: A balanced, everyday blend of the two, and the one most Japanese households use.

What’s in it: why the soya debate is different here

Fermentation and the radiation story

There’s plenty of debate about how well people in Western countries tolerate unfermented soya. Traditional miso is a different product: over the long fermentation, the koji enzymes break much of the soya protein down into small peptides and free amino acids. Miso is also at the centre of a Japanese myth about radiation. After the atomic bombings and later radiological research in Japan, it was claimed that a substance in long-aged miso called zybicolin binds certain radioactive elements (such as strontium) in the body so they leave via the gut. That story has never been confirmed in reliable studies in people.

Lactic acid bacteria and melanoidins

Like almost all fermented foods, long-aged, unpasteurised miso contains plenty of live lactic acid bacteria and yeasts. The long, Maillard-like fermentation also produces melanoidins – large molecules that give miso its reddish-brown colour. In lab tests, melanoidins act as antioxidants: they capture free radicals.

Salt without the blood pressure effect?

Miso is clearly salty. Interestingly, though, large long-term observational studies in Japan have repeatedly found that eating miso soup every day was not linked to higher systolic or diastolic blood pressure – unlike the same amount of plain table salt. Researchers suspect that certain bioactive peptides in the paste play a role, because they inhibit enzymes that raise blood pressure.

Important: never boil miso

Boiling kills the live lactic acid bacteria in unpasteurised miso and flattens its aroma. So stir the paste in right at the end of cooking. Take your wakame soup, ramen or veg curry off the heat completely (it should drop below 60-70 °C), put a ladle of the liquid in a cup, stir in your teaspoon of thick miso paste until smooth, then gently stir the mixture back into the pan. That way you keep the enzymes intact as well as the volatile, floral aroma.