Different varieties of mushrooms are sold dried. But the ones we use at home most often are black fungus / wood ears and shiitake so I’m using them as illustrations. They are used in so many Chinese and Japanese dishes that we find it practical to keep them in stock in dried form.
Why bother with dried mushrooms if fresh is available?
Two reasons. First, because dried mushrooms can be stored longer while fresh ones must be cooked within a day or two. And it’s just too time consuming to keep driving back and forth to the grocery.
Second, for the soaking water. It is so flavorful. You can use it to make soup and sauces. And you certainly won’t get soaking water when you use fresh mushrooms.
Tip for storing dried mushrooms
Dried mushrooms are often sold in vacuum-sealed packs. Vacuum-sealing means no air touches them so they stay good for a long time. But once opened, the dried mushrooms become subject to everything that fresh food is subjected to. We’re talking air, moisture and insects so small we might not even see them without looking very closely. In short, once the pack is opened, dried mushrooms will spoil faster.
How do we keep them good longer? First transfer them into containers with tight lids. Glass jars with screw-type caps are good. But air and moisture can still reach the mushrooms. So, you need silica gel. Just drop a few packets into the jar and your dried mushrooms will last longer.
How hot should the water be when rehydrating dried mushrooms?
Some cooks say the water should be hot, some say lukewarm while others say room temperature water is best. In my experience, they all work. The difference is the length of soaking time. The colder the water, the longer it takes to rehydrate dried mushrooms.
Because I don’t like wasting time, I like my mushrooms to be ready for cooking at the shortest time possible. That means using hot water. How hot? I boil water and leave it to cool for a minute then pour it over the dried mushrooms.
How long should dried mushrooms be soaked?
Again, that depends on the temperature of the water. And that also depends on what mushroom you’re rehydrating. Thin ones like wood ears and black fungus soaked in hot water will rehydrate fully in ten minutes. Larger and more dense mushrooms will take longer.
Dried shiitake, for instance, will rehydrate in twenty to thirty minutes in hot water. To help them soften faster, it is a good idea to flip them over once or twice during soaking.
How can you tell if dried mushroom has sufficiently rehydrated?
Dried mushrooms are smaller than fresh because the water content has been removed by means of dehydration. When rehydrated, they gradually swell to their original size as they absorb water. Once they reach thir original size, they will stop absorbing water and stop swelling. They means they are fully rehydrated and they don’t need to be soaked longer.
A final tip for rehydrating dried mushrooms
Use bowls large and deep enough so that the mushrooms have room to swell. You don’t want to overcrowd them so that each piece gets totally covered in water. With shiitake, you want them in a single layer for even rehydration.