The special flavor of dried shiitake mushrooms comes from two ingredients: mushroom essence and guanylic acid. In particular, guanylic acid has a umami intensity dozens of times greater than that of ordinary MSG. When rehydrating dried shiitake mushrooms, it is best to use lukewarm water at around 20°C—35°C. This not only allows the mushrooms to absorb water and soften more easily but also helps the guanylic acid to fully break down, releasing its umami flavor. Additionally, do not soak for too long. Once the mushroom caps are completely soft, lift them out and drain immediately.
If you add a little sugar to the soaking water, you can further reduce the loss of mushroom essence and guanylic acid during the water-changing process, resulting in a better-tasting mushroom in your cooking. Dried Black Fungus
Unlike shiitake mushrooms, dried black fungus should be rehydrated in cold water. If soaked in hot water, it will not rehydrate fully and will have a soft, sticky texture. Many of its nutrients will also dissolve and be lost. Although rehydrating black fungus in cold water takes longer, the result is a fresh, tender, and crisp texture. If you can't finish it all at once, as long as you rinse it with cold water once a day, it will not spoil for 3—5 days. Dried Squid
It must be rehydrated in an alkaline solution because alkali helps the squid return to its original fresh, tender, and soft state. When soaking, note that you should use lukewarm water in winter and cold water in summer. After soaking, rinse it in clean water to remove the alkaline solution. Dried Sea Cucumber
This is a more troublesome and time-consuming process. First, soak the sea cucumber in cold water for about 6 hours. Once it softens, cut open its abdomen and remove the internal grit. Then, rinse it in cold water for about 2 hours. Finally, place it in boiling weakly alkaline water and soak for about 2 hours, repeating this process twice. After removing it, rinse it thoroughly with clean water, and then "chill" it with ice cubes to better preserve its freshness. When rehydrating sea cucumber, avoid using salt, as it will prevent it from fully rehydrating and can easily lead to spoilage.