Corn smut is a fungal infection of maize, or corn, by Ustilago maydis. Among most United States corn farmers, it is considered a nuisance. In Latin American cuisine, however, it is eaten.
In Mexico, corn smut is called huitlacoche, a word derived from Nahuatl, possibly meaning "sleeping excrement," "raven's excrement," or "corn excrement." It replaces the kernels of corn with mushroom-like tumors or galls consisting of blueish black spores, fungal threads, and enlarged corn cells. It also decreases the yield of normal corn. In addition to its use in cuisine, corn smut can also be used to make silage, a feed for cattle and sheep.
Consumption of corn smut dates from the precolonial period, when corn plants were sometimes deliberately infected with the fungus by cutting the plant near the soil line. Native Americans of the southwest also used corn smut for its medicinal properties, notably to induce labor. Huitlacoche must be harvested when young, or there are too many spores, causing the galls to dry out. Corn smut grows best in periods of drought, at temperatures from 78°F to 93°F (25°C–34°C).
Ustilago maydis is required to infect corn at a specific stage in its life cycle. It cannot be maintained in laboratory conditions. Mature spores are released from the tumors in the corn kernels and spread by rain and wind.
Corn plants infected by corn smut typically develop symptoms of disease. One of the most common is chlorosis, or the insufficient production of chlorophyll, leading to pale yellow or white leaves. Reduced growth may also affect the plant, as well as red, blue, or purple pigmentation caused by anthocyanin. The corn also develops a scorched appearance.
In Mexico, huitlacoche is considered a delicacy and is more expensive than corn. It is usually sold fresh, but is also sometimes canned. It is served in a variety of foods, such as quesadillas and other tortilla-based dishes. Huitlacoche has an earthy, woody, savory yet sweet flavor similar to that of mushrooms.
In 1989, the James Beard Foundation, which promotes the culinary arts, attempted to popularize corn smut as a delicacy by holding a high-profile dinner and renaming huitlacoche the "Mexican truffle." The food gained a brief popularity, with Pennsylvania and Florida farms gaining permission from the United States Department of Agriculture (USDA) to intentionally infect their corn crops with Ustilago maydis. The initiative is still underway, and huitlacoche is increasingly available at farmer's markets.