Thanks Bethy! Regarding your question, miso will not lose all nutrition if you boil it. The main reason for not boiling miso is because it will cause it to separate (if you've ever seen a bowl of miso soup that's separated into a clear layer and miso layer at the bottom, the soup was likely boiled.) Another reason why it's not boiled is because boiling it will kill any live probiotics it may contain. That being said, adding it to hot soup in general (regardless of whether it is boiling or not) will probably kill the probiotics anyway, and most miso sold in the US is likely to to have been pasteurized (i.e. had all the probiotics killed), as miso with live cultures have a very short shelflife.

I love your site and your recipes, Marc!
Question: Is it true that one should never boil miso due to it losing all nutrition?

Hi Barbara, just reduce the amount of miso you add to the soup. There are a couple of other things to consider 1) Are you using powdered Dashi stock? If so, these tend to include a lot of salt, so this could be contributing to the problem. The solution here is to make your own dashi from scratch (recipe linked above). 2) White miso has significantly less salt than other types of miso so this is another option (though you should read my headnotes above as a lot of miso brands mislabel their miso as "white miso" in the US when in fact they are yellow miso.