You don’t have to be a chef to notice that some foods are more forgiving of kitchen mistakes than others. When you’re cooking vegetables (zucchini, let’s say), if you step out to take a call you might end up with too-soft glop. When you’re cooking meat, if you get distracted you could end up with a hockey puck. But mushrooms are much more forgiving. Even if an unexpected visitor calls you away from a pan of sautéing porcini for an hour, when you come back the mushrooms are likely to still be glossy and tender.
A few years ago, Dan Souza at Cook’s Science, run by America’s Test Kitchen, set out to confirm this phenomenon with an experiment. Souza spent 40 minutes steaming half-inch-thick planks of portobello mushroom, zucchini, and beef tenderloin. Every five minutes, he tested each sample with a fancy machine called a “CT3 Texture Analyzer,” which measured how much force would be required to “bite” three millimeters into each one. He also gave them to human tasters to try. Then he recorded the results.
After five minutes of steaming, the zucchini, beef, and mushroom were all equally tender, requiring about the same force for a “bite.” The mushrooms stayed the same for almost the whole 40 minutes, getting only 57% tougher in total—and still seemed tender to the tasters. In deep contrast, the beef was a whopping 293% more leathery after the same period of cooking. Meanwhile, the zucchini decreased 83% in firmness, turning into vegetable mush. So, what gives?
The answer, it turns out, is chitin, a fibrous polysaccharide—or cluster of chains of carbohydrate molecules—similar to keratin. It’s found in lobster and shrimp shells, insect wings, and the cells of fungi. It mostly serves to protect soft tissue in the natural world. (It’s also a great source of dietary fiber.)
And chitin is remarkably resistant to heat. In 2015, three Japanese researchers published a study exploring the material’s limits, which found that fungal cells with chitinous walls could withstand temperatures up to 380 C (716 F). In contrast, cellulose samples began to warp and eventually dissolved around 300 C. The authors attributed this remarkable strength to chitin’s structure. In mushrooms, chitin takes the form of fine bundles, each of which is made up of sheets that are layered in parallel but run in opposite directions. In α-chitin, the form most common in crustaceans, insects, and mushrooms, those sheets are held together by strong hydrogen bonds, making them even more durable.
All that is quite different from the molecular makeup of meat and vegetables. When the strands of the protein in meat are raw, they’re soft and flexible. But as they heat up, they contract together, pushing out moisture. The empty space causes the proteins to contract even further, eventually drying the meat out and turning it hard and tough. In vegetables, on the other hand, the hemicellulose and pectin (another polysaccharide) that hold plant cell walls together begin to break down after exposure to heat, releasing the bond between those cells. And, as the Japanese researchers found, they do so at much lower temperatures than chitin does.