Let’s say you’re growing a field of sweet corn. One day you go out to see how the developing ears are coming along, and you notice that rather than neat rows of yellow or white kernels, these ears are instead producing huge, strangely-shaped, gray mushy things! At this point you can either despair and plow your entire crop under, or you can get on the phone with your nearest high-end Mexican restaurant and make a ton of money.
You’ve got Corn Smut[i], otherwise known as Huitlacoche[ii].
Corn smut is generally considered a fungal disease of corn (Zea mays) and related wild grasses. It has an interesting two-stage life cycle; the fungus initially grows in soil or on corn stubble and produces spores, which are dispersed by air or by splashing water. Those that land on corn plants germinate and mate with each other, and then stimulate the corn plants to grow blisters or galls that eventually fill up with spores and burst—these spores overwinter in the soil or in corn stubble and then germinate to start the cycle over again (the on-soil generation does not need to mate). The galls and blisters reduce yield and can kill young plants. The galls can appear on any part of the plant, but when the fungus attacks the kernels themselves, it either converts the kernels to galls or turns them dark and oozy. It’s not unusual for an ear to have both infected and uninfected kernels. Either way, infected kernels are unsalable as corn.
Corn smut is not very common, as diseases go, and it’s considered only a minor problem—which is good, as there’s not much to be done about it. There’s no cure. There are varieties of corn bred specifically to resist smut, though, and avoiding damage by deer and other such problems can also increase corn resistance.
But the thing is that the gall-kernels are not only perfectly safe to eat, they are also, reportedly, delicious. They have long been considered a delicacy in Mexico and certain Indigenous cultures in the United States, and they are starting to become popular elsewhere, too. Corn-smut kernel galls are known as Huitlacoche, Cuitlacoche, Mexican Truffle, or by any of several other names. And if you can find someone who knows its worth, Huitlacoche can sell for considerably more than uninfected corn.
Identification & Description
Body: The kernels that become galls are larger, sometimes substantially larger, than uninfected kernels, and are often strangely shaped. They are pale gray when young but blacken with age. The interior flesh is soft (galls can be pulled apart by hand) and may be pale, marbled with black, or black, depending on age.
Spore Color: Black.
Smell: Nothing useful for identification.
Taste: Earthy and complex, variable.
Edibility: Choice.
Habitat: Grows exclusively in corn and related wild grasses.
Range: Anywhere corn grows.
Huitlacoche is a creature of contradiction. It is an edible fungus, but it is not a mushroom, and the galls are, in part, tissue produced by the corn plant at the insistence of the fungus. And while it grows on a cultivated crop, Huitlacoche is itself wild. Efforts are being made to develop cultivation methods (basically you buy spores and then inoculate your corn plants), for the most part it’s still just a matter of luck; the fungus appears where it wants to. Some varieties are more susceptible to infection than others, and since physical damage makes infection more likely, corn plants near the edge of a field, where deer often feed, or in flood-prone areas, are more likely to be infected than those near the center.
Very young galls can be bitter. Old galls start to blacken and ooze. Most Anglo-Americans who eat huitlacoche only like it in the narrow window between bitterness and blackening, but Mexicans traditionally cook with blackened galls, too.
Although Huitlacoche can be frozen, dried, pickled, or canned, it is best fresh. It does not keep in a fresh state for very long and doesn’t transport very well, so this “truffle” can be very hard to find.
Look-Alikes
Although huitlacoche does not look much like anything else, there are other smuts that attack corn and cause the growth of galls[iii]. They could confuse someone who has heard of huitlacoche but isn’t familiar with it, and the fact that they could all be called “corn smut” could also cause confusion.
The fungus that causes the growth of huitlacoche is Ustilago maydis and is often called Common Smut, Blister Smut, or Boil Smut. The fungus, Sphacelotheca reiliana, causes Head Smut, and infected ears become pear-shaped, black, and stringy. Ustilaginoidea virens causes false smut and is more common on rice but can attack corn as well[iv].
There are also fungi that attack other grain crops, and while they could not be confused with huitlacoche (which only grows on corn), someone could assume that because huitlacoche is good to eat, other fungal diseases of grain must be, too. That would be an incorrect assumption. Most of the others are not edible, and at least one (ergot, on rye) is dangerously toxic.
Benefits
The most obvious benefit of huitlacoche is that it tastes good[v]. It’s true that some find it an acquired taste, and when cooked it does turn black; many people do not find black food appetizing. However, it is a widely-enjoyed food with a rich and variable taste. The basic flavor is “mushroomy,” and it can replace many mushrooms in recipes, but there are other notes, often including a corn-like sweetness.
One of the most popular traditional ways to prepare huitlacoche is in quesadillas, but it is used as a filling in many different dishes otherwise made with meat or beans. In fact, huitlacoche not only replaces beans or meat in terms of taste but also in terms of nutrition[vi]. It has more total protein than corn, and it also contains the amino acid, lysine, a protein building-block that corn does not have. Eating huitlacoche and corn together thus delivers more protein than the total you’d get from eating the two separately, just as is the case with beans and corn.
Toxicity, Safety, and Side Effects
There are unconfirmed reports of illness as a result of eating huitlacoche, and it does contain chemical substances that may have a weakly medicinal or toxic effect[vii]. However, the fungus is widely consumed without ill effect.
It is worth noting that collecting huitlacoche from conventionally-grown corn fields—that is, not organic or pesticide-free—could be a bad idea. It’s possible the galls could absorb pesticides. For a similar reason, it’s probably also best not to gather from near roads.
References:
[i] Taylor, K., Volesky, N., Nischwitz, C., Murray, M. (2021). Corn Smut (Ustilago maydis). Utah State University Extension
[ii] Neimark, J. (2015). Scourge No More: Chefs Invite Corn Fungus to the Plate. NPR
[iii] Mohan, S.K., Hamm, P.B., Clough, G.H., duToit, L.J. (2013). Corn Smuts. PNW 647: July.
[iv] Abbas, H.K., Sciumbato, G., Keeling, B. (2002). First Report of False Smut of Corn (Zea mays) in the Mississippi Delta. Plant Disease 86(10): 1179.
[v] Bergo, A. (2023). Huitlacoche. Forager-Chef
[vi] Neimark, J. (2015). Scourge No More: Chefs Invite Corn Fungus to the Plate. NPR
[vii] Deane (n.d.) Corn Smut, Mexican Truffles. Eat the Weeds
