The last meals of men and women buried centuries ago in the ancient city of Casas Grandes were dominated by corn, new research has found — from ground maize, to corn smut, to what archaeologists say is the first conclusive evidence of corn beer in the Greater Southwest.

And these clues were found in a long-overlooked source: the fossilized plaque on the teeth of the dead.

Archaeologists say these and other findings are providing important insights into the diet and lifeways of one of the most influential prehistoric cities in the region.

“The results of this study offer some of the first hard evidence for the production of corn beer, consumption of corn smut, and food processing methods,” said Daniel King, a graduate student in anthropology at Brigham Young University, who led the research.

“It is a step forward in understanding Casas Grandes human-plant interactions, especially diet.”

Casas Grandes, also known as Paquime, was a large settlement on the fringes of the Mogollon culture to the north and Mesoamerica to the south.

At its peak in the 14th century, the city was home to as many as 3,000 people, likely serving as a trade center, trafficking goods and channelling cultural influences between what’s now central Mexico and the southwestern U.S.

Situated in Chihuahua some 130 kilometers, or 80 miles, from the New Mexico border, Casas Grandes was excavated in the 1950s and ‘60s, revealing hundreds of human remains — some buried, some dismembered and placed in urns, others apparently left out in the open.

Now, a new project undertaken by Dr. Anne Katzenberg of the University of Calgary is revisiting those remains, in an effort to learn more about the people who lived and worked in the prehistoric city.

And King and his colleagues sought to do their part, by analyzing the teeth of the dead.

Specifically, they studied the tooth calculus of more than a hundred sets of human remains.

“Calculus is fossilized tooth tartar,” King said.

“If teeth aren’t cleaned regularly, then the tartar, which can trap pretty much anything in it, such as algae, plants, fungus, or fibers, will slowly mineralize with everything stuck in it and turn into calculus, while the microremains turn into microfossils.”

To get at this microscopic evidence, the team recovered tartar from the remains of 110 people found within the ancient city and from other sites in the Casas Grandes River valley, all buried between 700 and 1450 CE.

Of those 110 samples, 63 yielded some sort of microscopic remains.

The most common traces the researchers found were starch granules, mostly bits of corn, which accounted for 36 percent of the samples.

Also common were phytoliths — tiny mineral fragments — that came from grasses and squash.

And more than 10 percent of the samples revealed the presence of corn smut — an edible, nutritious fungus that grows on corn and is still considered a delicacy, known today by its Aztec name, huitlacoche. [Learn more about what ancient teeth can tell us: “Severed Heads, Skull Bowls Found in California Graves Were Tributes, Not War Trophies, Study Finds“]

But while corn appears often in the dental record of Casas Grandes’ dead, that’s not necessarily a reflection of the population’s diet as a whole, King noted.

“Given the nature of calculus, any microremains recovered are going to be from the last days or weeks of the person’s life, maybe a month or two, but not longer,” he explained.

“So reconstructing diet, in the long term sense, doesn’t work with calculus.

“However,” he added, “identifying specific foodstuffs — like corn beer, fish, chile, et cetera — is useful, as many of them can’t be seen in the results of other studies.”

And in this regard, King said, the “most interesting results” of his team’s research was the discovery of corn alcohol.

Three of the samples revealed granules of maize that bore the unmistakable signs of fermentation, he said — including swelling and fragmentation caused by being heated at three distinct temperatures, and striations created by the fermenting process.

These bloated, broken grains seem to be the result of making chicha — a corn beer whose use has been recorded in Central and South America for as much as 5,000 years, King said.

In those cultures, brewing and consuming chicha is thought to have held ceremonial value, but it may have held other functions as well, he noted.

“We don’t have enough information to determine [chicha’s] use,” King said.

“Based on ethnographic accounts, we default to ‘ritual’, although I always think that’s a cop-out answer.

“We know modern groups used corn beer or similar drinks in religious ceremonies, so that’s all we can go off of.” [See what else ancient Americans drank: “Cocoa, Caffeinated ‘Black Drink’ Were Widespread in Pre-Contact Southwest, Study Finds“]

In addition, King noted, the burial contexts of the samples haven’t yet been analyzed, so archaeologists can’t yet draw conclusions about whether beer consumption was limited, for example, to a certain social class.

Moreover, he added, this is the first “substantial evidence” of corn beer in the Greater Southwest, so it’s possible that chicha may have served a different function in Casas Grandes than it did in Mesoamerica.

When it comes to beer in the southwestern archaeological record, he said, “almost nothing exists for northern Mexico or the American Southwest. The results we posted may be the first of their kind for this region.”

Some ceramic fragments found near Casas Grandes, for example, have displayed microscopic “pitting” that could have been caused by fermentation, he noted.

And a study in 2007 found traces consistent with fermentation in potsherds from Ancestral Puebloan settlements in New Mexico; but researchers cautioned that the fermentation may have been accidental, and the findings were described as “provocative but inconclusive.”

King’s new findings, then, raise the question of how the custom of brewing corn beer arrived at Casas Grandes, as well as when, and by whom.

“The best archaeological evidence we have for corn beer and other alcoholic drinks comes from Peru or Mesoamerica,” King said.

“So, if anything, the idea for corn fermentation came up from the south, but that is still conjecture at this point.”

As for when beer came to town, his findings do provide some insights.

His team studied teeth dating back as far as the year 700, but the fermented granules were only detected on remains dated to the so-called Medio Period of Casas Grandes — a cultural heyday that spanned from about 1200 CE to 1450 CE — suggesting that chicha might have been a relatively recent phenomenon.

“Our results show that maize was used throughout various time periods, but evidence for maize fermentation only comes from the Medio period,” he said.

“This is not to say such use did not exist in the [earlier] period, only that our results don’t currently support that idea.”

But whether it was brewed, chewed, or cooked, the corn of Casas Grandes may, in time, teach us volumes, not just about diet, but also about the social interactions that shaped one of the most important cultural crossroads in ancient North America. [Discover another recent find made nearby: “Ancient Grave of Teenage Girl May Reveal Secrets of Southwest’s Earliest Farmers“]

“The continuity of maize use throughout the two time periods is important,” King said.

“It may suggest a continuity of people, thereby supporting an in situ development.

“Turning maize into beer during the Medio period, however, could suggest an influx of new ideas — or perhaps even people — during that time, which might indicate outside influence — either foreigners coming to Casas Grandes, or locals traveling and coming back with new ideas.”