Why is Miso so Salty?

Written by Michael Grant in Miso

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Miso takes a long time to ferment and age to reach its best flavor profile.  During this time the soybean mash mixture goes through several stages of maturation.  This gives unwanted micro-organisms time to grow on the miso and spoil it.  Salt is used For two reasons:

  • To prevent any of these micro-organisms from gaining a foothold in the ferment while the lactic acid bacteria acidify the mash. 
  • To stop the growth of Aspergillus oryzae mold which produces the koji

The salt in the miso acts as a food preservative by reducing the available water  in the miso by binding to the water molecules.  This makes it harder for spoilage microbes to begin to grow in the miso.

Miso is made with a multi-step process which includes a pre-inoculation step where the mold Aspergillus oryzae is grown on a rice or barley substrate to make koji.  The active koji is then added to the warm soybean and rice/barley mash and thoroughly mixed.  Salt is then added into the mash before it is packed into ageing containers and sealed. It is then aged for at least a month to up to several years.

Once the salt is added the Aspergillus oryzae mold growth is arrested but the enzymes which convert the starches in the soybeans into sugars are still present.  These enzymes convert the starches from the soybean mash into sugars.   These sugars are then used for fuel which the salt tolerant lactic acid bacteria and the yeast Zygosaccharomyces rouxii use as energy for growth.  With enough available sugars and a salty environment they quickly dominate the fermentation preventing the spoilage of the miso.

Depending on the type of miso being made more or less salt is added.  White miso which is aged the shortest amount of time usually contains the least amount of salt.  Red miso which can be aged for up to two years or more needs more salt to prevent spoilage.

Salt levels of each type of miso

Not all types and brands of miso contain the same amount of salt.  The ingredient variations, amount of time it is aged, the brand and the aging conditions all affect the amount of salt in the miso.

The following chart shows some of the popular brands and their salt content in milligrams.

Miso brand salt content
tbsn tsp 100 g
Shiro Miso 860 287 5059
Dashi miso soybean paste 830 277 4882
Awase 860 287 5059
Hikari
Hikari Organic Miso Paste 719 240 4229
Organic Miso White 719 240 4229
Organic Miso Red 733 244 4312
Organic Mild Sodium 600 200 3529
Organic Saikyo Sweet 470 157 2765
Enjuku Koji Miso Reduced Sodium 578 193 3400
Hikari Kome Koshi Miso 782 261 4600
Hikari Inaka Miso 748 249 4400
Hikari Dashi Iri Miso 884 295 5200
Cold Mountain Miso
Light Yellow Miso (Shinshu Shiro Miso) 1020 340 6000
Red Miso (Aka Miso) 1020 340 6000
Mellow White Miso 660 220 3882
Mellow Red Miso 660 220 3882
Kyoto White Miso 420 140 2471
Kyoto Red Miso 1020 340 6000
Organic Ville
Organic Brown Rice Miso 720 240 4235
Orgainc Red Miso 747 249 4394
Organic Saikyo Sweet Miso 413 138 2429
Amano
Aka Miso 510 230 3000
Genmai Miso 660 220 3882
Mugi Miso 660 220 3882
Shiro Miso 510 170 3000
Shirakiku
Dashi-iri Awase Miso 830 277 4882
Average 717 241 4216

Overall the amount of sodium in miso is fairly consistent.  Some brands like Cold Mountain Miso have a higher sodium content in some types of miso but also offer lower sodium miso.  With an average of 717mg per tablespoon of all the types in the table.  This indicates that you shouldn’t choose your miso by the amount of salt but rather by its taste and versatility.

Miso has a wide flavor spectrum.  Different types are better for some recipes so don’t be limited by only using one type of miso, instead have a variety on hand for different uses.  The light sweet Miso is great for sweet sauces and desserts whereas mature red miso is better for soups and marinades.

Does the amount of sodium in Miso limit the amount I should eat?

The concern with eating a lot of miso is the sodium content.  Miso requires a high percentage of salt to be added to inhibit the growth of unwanted micro-organisms during its long fermentation and aging time.  During the fermentation and maturation of the miso various vitamins and other compounds are produced which are vital for our health, as a result, miso has been labeled a super-food with high health building effects.  For an in depth chart on the nutritional value of miso can be found in the post Natto vs Miso.

It is well known that a diet high in salt can have detrimental effects on cardiovascular health, but are all high sodium content foods bad for the heart?

There have recently been several studies on the effect of miso and cardiovascular health which indicate that not only does the salt content in the miso not affect the blood pressure but that miso helps to lower the heart rate.  The study showed that individuals which ate a higher amount of miso soup had lower heart rates.  Another study showed a lower blood pressure from eating miso over the same amount of raw salt while reducing the chances of a variety of cancers.

These studies show that simply reducing the amount of salt added to the diet is not the way to cardiovascular health.   That is a knee jerk reaction which may or may not lead to a healthy lifestyle.

Salt content of Miso soup compared with other popular soups

Miso has a reputation for having a high salt content but what about other popular soups like Chicken Noodle or French onion.  Here is a list of popular soups along with their sodium content.

  Popular Soup Sodium Content
Soup name Store Bought Home Made
Pho 384 384
Borscht 940 591
Split Pea 680 420
Chicken Noodle 890 523
Mulligatawny 640 617
Gazpacho 739 650
Minestrone 746 400
Hot and Sour 876 1250
Miso 998 515
Manhattan Clam Chowder 1000 925
French Onion 1028 703.6
Vegetable Beef 890 240

As you can see Miso Soup does not contain the most amount of sodium of all the soups on the list and if you make it yourself you can control the amount of sodium by adding more or less miso, include or exclude other high sodium content ingredients such as seaweed or soy sauce both of which are also high in sodium.

Michael Grant

Mike has been an enthusiast of fermentation for over ten years. With humble beginnings of making kombucha for himself to the intricacies of making miso, vinegar and kefir. He makes a wide variety of fermented foods and drinks for his own consumption and family and friends. Being a serial learner he began experimenting with a wide variety of fermented products and learning widely from books, online from content and scientific studies about fermentation, its health benefits, how to use fermented food products in everyday life and the various techniques used to produce them both traditionally and commercially. With a focus on producing his own fermented products in an urban environment with little access to garden space he began Urban Fermentation to help others who want to get the benefits of fermentation in their lives. He provides a wide variety of content covering fermented drinks like kombucha and water kefir, milk kefir and yogurt, vinegar production and lacto-fermentation such as pickles, sauerkraut for those who have to rely on others for food production. With an insatiable hunger to know more about fermentation from all nations and cultures he also has learned to make natto, miso and soy sauce, with more to come as the body of knowledge about fermentation is constantly expanding and becoming more popular as time passes.

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