HOT-AND-SOUR SOUP

At the outset, we knew we could expect three challenges when trying to make this soup in an American kitchen. First, we would need to find substitutes for a few hard-to-find ingredients. Second, we had to arrive at the correct balance of flavors. Hot-and-sour soup should be complex, with hot, spicy, and sour flavors most prominent. Third, we had to perfect the texture, which should be silky and thick.

We focused first on the hard-to-find ingredients, in particular wood ear fungus (a kind of mushroom) and lily buds (which come from tiger lilies), both of which have a chewy texture and earthy flavor. We found that dried shiitake mushrooms were the best substitute.

While dried shiitakes are a good visual replacement for wood ear fungus, the soup looked odd without the thinshredded bits of lily bud. As suggested in some sources, we tested both shredded leeks and bamboo shoots. Bamboo shoots seemed more authentic and were easier to prepare.

Almost every recipe we researched included chicken stock, soy sauce, vinegar, sesame oil, pepper, tofu, and egg. The type of vinegar and pepper used varied.

We tested distilled white, rice, white wine, and apple cider vinegars and found that mild rice vinegar provided the necessary sour notes without adding any distracting flavors. Chinese black vinegar (an ingredient available mostly in Asian markets) is also often added for flavor and color. Some sources we consulted suggested using Worcestershire sauce as a substitute, and it worked beautifully, adding the dark color and complex, pungent flavor the soup needed.

We tested cayenne, white, and black pepper, alone and in combination. Cayenne was the testers' least favorite. It created a reddish color and an overpoweringly hot flavor. Black and white pepper were equally enjoyed. Since black pepper is a more common item, we chose it for our recipe.

The final issue that remained to be tested was thickening the soup. At this point, we knew that a liberal amount of cornstarch would be needed to create a thick broth. When we used just two or three tablespoons, the heavy ingredients in the soup (tofu, pork, and vegetables) fell to the bottom of the pot. In the end, we found that one-third cup of cornstarch is needed to thicken eight cups of broth.

The point at which the cornstarch is added is also important. When added after the acid (the rice vinegar), the cornstarch often failed to thicken the soup. Several food scientists we spoke to explained that because acid can prevent starch granules from bonding, it is preferable to add the acid after the cornstarch has dissolved and its granules bonded together to form the dense network that thickens the broth. Once the acid is added, the soup must not cook too long, or you again run the risk of causing the soup to thin out.