Mushrooms

We’re not sure what show you saw, but this question was also raised by readers who saw an episode of “How It’s Made,” in which mushrooms were grown in mushroom mycelium put atop wheat berries. Here’s a basic explanation of how white mushrooms are grown, from the Mushroom Council: Mushrooms grow from microscopic spores, not seeds. Spores are used to inoculate grains or seeds to produce a product called spawn (the mushroom farmer’s equivalent of seed). Spawn is made by sterilizing a mixture of rye, wheat, millet or other grain plus water and chalk. Mushrooms must get all their nutrients from organic matter in their growing medium, which is called compost and is scientifically formulated of materials such as straw, corn cobs, cotton seed and cocoa seed hulls, gypsum and nitrogen supplements. The compost is pasteurized and spawn is worked into the compost. In two to three weeks, the compost becomes filled with the root structure of the mushroom, a network of lacy white filaments called mycelium. At that point, a layer of pasteurized peat moss is spread over the compost. Eventually, tiny white protrusions form on the mycelium and push up through the peat moss. Eventually they become mushroom caps, which are actually the fruit of the plant, just as a tomato is the fruit of a tomato plant. In addition to the Mushroom Council, we talked to experts at a spawn company, the Mushroom Research Center at Pennsylvania State University, and a Penn State food scientist who specializes in mushrooms. All agreed that it is highly unlikely that mushroom growing practices would result in mushrooms being cross-contaminated. Although cross-contamination of mushrooms by glutencontaining grains in spawn has not been studied, researchers have looked into allergen contamination of mushrooms by peanuts and soy. One study concluded that supplements/fertilizers made from peanut and soy proteins introduced to the mushroom crop at the same time as the spawn did not cross-contaminate the mushrooms.