Soaking mushrooms?

Don’t throw the water away!

Have you been soaking dried mushrooms, shiitake maybe? Don’t throw the soaking water away – it’s golden!

In recipes, I have always advocated keeping the soaking water after reconstituting dried mushrooms. Over a few hours of soaking, the water develops a rich, earthy aroma and a deep amber colour. I’d always assumed this was an indication that some of the goodness from the mushrooms had leached into the water – creating a nutrient-rich leachate – and it turns out that assumption was correct.

The science of soaking water

Scientists have shown that something important happens when dried shiitake mushrooms are soaked in water (preferably a long cool soak, but warm if you’re in a hurry). Studies suggest that roughly half of these minerals move into the soaking liquid during rehydration. Research measuring rehydrated shiitake found that the soaking water can carry away part of their minerals and nutrients – for example potassium – as well as amino acids that give mushrooms their famous umami taste, guanylic acid (one of the key flavour compounds in shiitake), and even small amounts of B vitamins and natural antioxidants.

This means that the soaking water is far too valuable to throw away.

Simmering and boiling

And that is before any cooking takes place.

Water-soluble vitamins and minerals have already leached partially into the water during soaking. Even more of the remaining soluble nutrients from the mushrooms themselves will leach out during cooking, directly into the broth. Heat breaks down the cell walls and structural polysaccharides, releasing additional compounds that cold soaking alone cannot extract, including bound amino acids, larger phenolic antioxidants and more minerals such as potassium and selenium.

Cooking, especially with prolonged simmering, leads to further leaching of bioactive compounds such as B vitamins, eritadenine and amino acids like glutamate. Glutamate is interesting as it is responsible for the savoury, umami taste associated with shiitake.

Nutrient losses

Losses at a glance:

• B vitamins (thiamine, niacin): major transfer – 80–95% loss
• Minerals (potassium, selenium): substantial leaching into liquid
• Free amino acids (glutamate): leach into liquid, add umami flavour
• Polyphenols, flavonoids, eritadenine: partial loss, more retained if cooking gently
• Polysaccharides (β-glucans): mostly remain in mushroom tissue

Adding the soaking water straight into broths or toppings ensures that the minerals, flavour compounds and other nutrients are saved and kept in the final dish, along with the mushrooms themselves. Even if you’re not cooking the mushrooms in a broth or topping but in water, those rehydrated mushrooms will also free different amino acids, small proteins, antioxidant phenolics and other small molecules into the liquid. So that shouldn’t be discarded.

By retaining and cooking with the soaking water, we can capture not just the goodness of the mushroom itself but also all the nutrients that would otherwise be lost.

This simple step preserves minerals, flavours and nutrients, making the most of every part of the dried shiitake – perfect for a no-waste cooking hack that’s both tasty and responsible.

Don’t throw that water away!

 

 

 

Important Considerations:

  • Always consult your veterinarian before making any significant dietary changes, particularly where there are pre-existing health conditions or dietary restrictions.
  • If you are feeding commercial food, check the label for ingredients before giving more. Excessive intake of any foods can have adverse effects.
  • Ensure (where possible) that you use high-quality, organic products specifically formulated for pets (or better still, human grade ingredients) to avoid any potential adverse effects.
  • Introduce new foods gradually to avoid adverse effects such as gastrointestinal upset or diarrhoea.
  • I provide nutritional information purely as a helpful guide. Nutritional information on ingredients is obtained from the US Department of Agriculture’s FoodData Central site (https://fdc.nal.usda.gov/index.html) and any nutritional information provided in recipes is based on an online calculator: calories and other information will vary based on brands, ingredients and other factors.
  • Check nutrient levels and recommendations for your dog’s weight, age and activity. For example this nutritional guideline produced by FEDIAF.
  • I am not a professional canine nutritionist but supporting research is cited.
  • The recipes shared were created by me and tested in my kitchen – and tasted and approved by our doggy friends!