In most cases, we do recommend rehydrating your mushrooms (especially if replacing fresh in a recipe), but there are many instances in which you can use them without reconstituting them. If they are being added to soup or stew and the recipe doesn't call for sautéing first (and they are in the cook pot for around 30 minutes or more), they will perk up in the pot. Another way to use dried mushrooms without rehydrating is to grind them and use them in a seasoning blend like we have done with this morel encrusted leg of lamb recipe and this umami seasoning salt.