Seven percent of all American adults believe that chocolate milk comes from brown cows, according to a nationally representative online survey commissioned by the Innovation Center of U.S. Dairy.

If you do the math, that works out to 16.4 million misinformed, milk-drinking people. The equivalent of the population of Pennsylvania (and then some!) does not know that chocolate milk is milk, cocoa and sugar.

But while the survey has attracted snorts and jeers from some corners -- "um, guys, (milk) comes from cows -- and not just the brown kind," snarked Food & Wine -- the most surprising thing about this figure may actually be that it isn't higher.

For decades, observers in agriculture, nutrition and education have griped that many Americans are basically agriculturally illiterate. They don't know where food is grown, how it gets to stores -- or even, in the case of chocolate milk, what's in it.

One Department of Agriculture study, commissioned in the early '90s, found that nearly 1 in 5 adults did not know that hamburgers are made from beef. Many more lacked familiarity with basic farming facts, like how big U.S. farms typically are and what food animals eat.

Experts in ag education aren't convinced that much has changed in the intervening decades.

"At the end of the day, it's an exposure issue," said Cecily Upton, co-founder of the nonprofit FoodCorps, which brings agricultural and nutrition education into elementary schools. "Right now, we're conditioned to think that if you need food, you go to the store. Nothing in our educational framework teaches kids where food comes from before that point."

Upton and other educators are quick to caution that these conclusions don't apply across the board. Studies have shown that people who live in agricultural communities tend to know a bit more about where their food comes from, as do people with higher education levels and household incomes.

But in some populations, confusion about basic food facts can skew pretty high. When one team of researchers interviewed fourth-, fifth- and sixth-graders at an urban California high school, they found that more than half of them didn't know pickles were cucumbers, or that onions and lettuce were plants. Four in 10 didn't know that hamburgers came from cows. And 3 in 10 didn't know that cheese is made from milk.

"All informants recalled the names of common foods in raw form and most knew foods were grown on farms or in gardens," the researchers concluded. "They did not, however, possess schema necessary to articulate an understanding of post-production activities nor the agricultural crop origin of common foods."

In some ways, this ignorance is perfectly logical. The writer and historian Ann Vileisis has argued that it developed in lockstep with the industrial food system.

As more Americans moved into cities in the mid-1800s, she writes in the book "Kitchen Literacy," fewer were involved in food production or processing. That trend was exacerbated by innovations in transportation and manufacturing that made it possible to ship foods in different forms, and over great distances.

By the time uniformity, hygiene and brand loyalty became modern ideals - the latter frequently encouraged by emerging food companies in well-funded ad campaigns - many Americans couldn't imagine the origins of the boxed cereals or shrink-wrapped hot dogs in their kitchens.

Today, many Americans only experience food as an industrial product that doesn't look much like the original animal or plant: The USDA says orange juice is the most popular "fruit" in America, and processed potatoes - in the form of french fries and chips - rank among the top vegetables.

"Indifference about the origins and production of foods became a norm of urban culture, laying the groundwork for a modern food sensibility that would spread all across America in the decades that followed," Vileisis wrote, of the 20th century. "Within a relatively brief period, the average distance from farm to kitchen had grown from a short walk down the garden path to a convoluted, 1,500-mile energy-guzzling journey by rail and truck."

The past 20 years have seen the birth of a movement to reverse this gap, with agriculture and nutrition groups working to get ag education back into classrooms.

Aside from FoodCorps, which worked with slightly more than 100,000 students this year, groups like the National Agriculture in the Classroom Organization and the American Farm Bureau Foundation are actively working with K-12 teachers across the country to add nutrition, farm technology and agricultural economics to lessons in social studies, science and health. The USDA Farm to School program, which awarded $5 million in grants for the 2017-2018 school year on Monday, also funds projects on agriculture education.

For National Dairy Month, which is June, NACO has been featuring a kindergarten-level lesson on dairy. Among its main takeaways: milk -- plain, unflavored, boring white milk -- comes from cows, not the grocery case.

Nutritionists and food-system reformers say these basic lessons are critical to raising kids who know how to eat healthfully - an important aid to tackling heart disease and obesity.

Meanwhile, farm groups argue the lack of basic food knowledge can lead to poor policy decisions.

A 2012 white paper from the National Institute for Animal Agriculture blamed consumers for what it considers bad farm regulations: "One factor driving today's regulatory environment ... is pressure applied by consumers, the authors wrote. "Unfortunately, a majority of today's consumers are at least three generations removed from agriculture, are not literate about where food comes from and how it is produced."

Upton, of FoodCorps, said everyone could benefit from a better understanding of agriculture.

"We still get kids who are surprised that a french fry comes from a potato, or that a pickle is a cucumber," she said. "... Knowledge is power. Without it, we can't make informed decisions."

-- By Caitlin Dewey