Need to keep your picnic cool? Try mushrooms instead of dry ice! Researchers document a remarkable cooling ability in yeast, mold, and mushrooms, thanks to evaporation
“Cool as a cucumber” might be better phrased as “cool as a mushroom.” A research team has found that mushrooms and other fungi, including yeast and molds, stay cooler than their surroundings—and has also explained how they stay so chill. The contain a lot of water—just think how mushrooms shrink when cooked—and gradually release it in a fungal form of sweating that lowers their temperature, the microbiologists report this week in the Proceedings of the National Academy of Sciences.
“It’s kind of a neat finding,” says Christopher Still, an ecophysiologist at Oregon State University who was not involved with the work. Mostly for fun, the team even built a picnic cooler powered by mushrooms.
Walking in the woods during the COVID-19 pandemic, Johns Hopkins University microbiologist Radamés Cordero was trying out his lab’s new thermal camera, which records infrared—heat—as images. He and his colleague Arturo Casadevall planned to use the camera to see how the dark pigments of some fungi influence their surface temperature. During his hikes, Cordero imaged about 20 kinds of wild mushrooms, and all—regardless of color—were cooler than their surroundings.
Following up in the lab, the researchers found that some species, such as the brown American star-footed amanita, were just 1°C or 2°C cooler than their surroundings, but the oyster mushroom Pleurotus ostreatus was almost 6°C cooler. Moreover, 19 kinds of molds and yeast, including Brewer’s yeast, the mold that makes penicillin, and a few human pathogens, were also cool, particularly near the center of their colonies. Even at air temperatures close to freezing, the colonies were about 1°C colder.
The temperatures of the single-cell fungi were a surprise, because compared with mushrooms they have much less surface area per volume, even when grouped into colonies, for losing heat. But the work suggests “this phenomenon is a widespread feature of the fungal kingdom,” Cordero says. (Only after his team’s initial research did he discover that another team showed more than 20 years ago that at least one kind of cultivated mushroom keeps its cool.)
By dehydrating mushrooms or measuring their cooling ability at different air humidities, the researchers determined that the chilling effect stems from water evaporating from the fungi—the equivalent of sweating on a hot day. The complex gill architectures on the undersides of mushroom caps increase the surface area for such cooling. Plant leaves similarly cool themselves, by releasing water through pores, but their method is usually not as effective.
How the fungi benefit from staying so cool is unclear. It might aid in the development or release of spores from the mushroom caps, or “it may just be that this kingdom prefers a lower temperature,” Casadevall says. “That would be a neat thing to explore,” Still says.
In the meantime, the cool mushrooms can be put to work. Cordero and Casadevall put two air holes in a small Styrofoam packing box containing less than a half-kilogram of button mushrooms, installed a computer exhaust fan in one hole to draw air through it, and put the box into a larger Styrofoam container. With the fan on, the larger container’s temperature dropped 10°C within 40 minutes and stayed there for half an hour. “You are not going to freeze water,” through mushroom cooling, Casadevall says. But the prototype could easily keep a six-pack and lunch chilled for a quick picnic, he says, “and you can eat the [mushrooms] afterwards.”