The Reason Why Miso is so Salty

Miso is one of my favorite foods, but I used to think it was too salty when I was younger. Now, all grown up, understanding the reason Miso is so salty and how to use it properly, I decided to write this blog post since more people might have this same question.

So, why is miso so salty? The short answer is: Salt is used to preserve the miso and make sure no bad bacteria grow in the miso paste. There is a direct relation between the amount of salt and the time it spends fermenting (months, sometimes years). The more salt, the more time fermenting.

For each kind of miso, there is a different amount of saltiness, but also a whole range of different flavors: earthy, fruity, sweet, umami. There are also misos with a reduced quantity of sodium!

But, Why Salt?

Salt is capable of preserving a variety of foods for months, even years. It has been used for ages, from ancient Japan to Greece, Egypt, and even the Vikings! This preservation method was essential in the old times for the survival of people since food would not be available all year round and there was no such thing as a freezer or cans.

Besides the extraordinary preservation power, which will be explained further during this post, this method also gives food a unique and rich flavor that has captivated enthusiasts until today (me being one of them!). There are new and effective methods to preserve food, but nothing can give that funkiness and umami, unparalleled delicious taste that a proper homemade fermentation can.

There are two ways to use salt to preserve food: salting (with dry salt) and using a brine (a solution with salt and water). Both are effective and sometimes used together, acting on different areas of food preservation.

Salting: Salt dehydrates the food, removing the water from it. Without water, most bacteria can not grow, including the bacteria that cause spoilage and food poisoning.

Salt is effective as a preservative because it reduces the water activity of foods. The water activity of a food is the amount of unbound water available for microbial growth and chemical reactions. Salt’s ability to decrease water activity is thought to be due to the ability of sodium and chloride ions to associate with water molecules (Fennema, 1996Potter and Hotchkiss, 1995).

Institute of Medicine (US) Committee on Strategies to Reduce Sodium Intake; Henney JE, Taylor CL, Boon CS, editors. Washington (DC): National Academies Press (US); 2010.

Brine: The food is immersed in a solution made of salt and water. For each kind of food, there is a different ratio of the mix. It is mostly used for the fermentation of vegetables or the first step of meat dehydration.

Salt favors the growth of these more salt-tolerant, beneficial organisms while inhibiting the growth of undesirable spoilage bacteria and fungi naturally present in these foods (Doyle et al., 2001). Salt also helps to draw water and sugars out of plant tissues during fermentation of vegetables.

Institute of Medicine (US) Committee on Strategies to Reduce Sodium Intake; Henney JE, Taylor CL, Boon CS, editors. Washington (DC): National Academies Press (US); 2010.

What about the salt in miso? Miso is made of three main ingredients:

  • Beans: Traditionally are used soya beans, but can be made with almost any kind of bean, including chickpea.
  • Koji Rice: Koji (aka Aspergillus oryzae) is a kind of mold responsible for ferment the miso, producing its unique flavor, and helping the preservation process. This good kind of mold is mixed with rice and dehydrated, being activated just before the moment to prepare the miso mix for fermenting.
  • Salt: Creates the perfect environment for the koji to grow and for the bad bacteria and germs to die.

Miso preparation

For the process of miso preparation, the beans are cooked and then mashed and mixed with salt and koji rice, so it is created an environment with all the properties described above, perfect for preservation and fermentation.

And How Much Salt is Used in Miso?

Each kind of miso has a different ratio between those three elements that influence the taste and the amount of salt (or how salty is the miso).

White Miso (aka Shiromiso) has a higher percentage of koji rice than beans and salt. Of the three main kinds, is the least salty one. Also, it ferments for less time, leading to a light and slightly sweet taste.

Red Miso (aka Akamiso) undergoes a longer fermentation process, has a higher amount of salt, with a similar quantity of beans and koji rice. It has a mature and umami flavor.

Yellow Miso (aka Awasemiso) is the more versatile one because is a mix between the red and the white miso. In terms of saltiness, it falls right in the middle.

Inside each category of miso, there are variations in flavor. Below is a table with the ratios suggested per Kirsten Shockey, author of the book Miso, Tempeh, Natto & Other Tasty Ferments, from the sweetest (the white on top) to the saltiest (the red on the bottom).

Dried BeansKoji SaltTime Fermenting
White1x3x4.5% weight of bean + koji3 weeks
White1x3x6% weight of bean + koji2 months
Yellow1x2x10% weight of bean + koji6 months
Red1x1x12% weight of bean + koji12 months
Red1x0.5x16% weight of bean + koji24 months
Ratio of salt and ingredients as per Kirsten Shockey book (2019).

These ratios are for the preparation of miso, so the final product will have some variations. If you want to know the amount of salt in the miso you are consuming, always check the label, which is the best place to find information on a determined product.

What About Reduced-Sodium Miso?

Reduced-sodium misos are not necessarily low in sodium, but they will have had their sodium amount reduced artificially after preparation or been prepared with a lower salt percentage and some kind of preservative.

You don`t need to buy reduced-sodium miso to be able to enjoy this marvelous food, there are ways to properly use regular miso and not leave the food too salty.

You just have to combine the right ingredients, use less salt when cooking with it, and experiment! There are many recipes out there. Test it, change it, taste it and start again. Soon you will be mastering the amount of miso to put in each recipe and even incorporating some miso into old recipes for that punch of delicious umaminess!

Are There Any Drawbacks?

Knowing miso has a high amount of salt might worry some people and that is completely understandable, we see everywhere that we should take care of our sodium intake. But the sodium present in miso is not the same as the sodium present in highly processed foods and should not be treated the same.

In general, it is safe to consume normal amounts of miso without any risk of high blood pressure or any condition like this (But, of course, always talk to your doctor if you have concerns). Miso also has an enormous variety of benefits and nutrients and is one of the healthiest foods.

I am not qualified to explain why Miso is healthy and not a big concern for blood pressure issues, but there is a lot of scientific research on the topic. If you are worried about the amount of sodium intake and the health impacts it could have on your health, I encourage you to watch this video by Dr. Michael Greger on He is more than qualified to answer this question and has videos and articles on the subject.

Here is a small sample of what the says and I think it summarizes well this question

“Indeed, miso paste, a whole soy food, can be used as a “green light” source of saltiness when cooking”

Michael Greger M.D. FACLM