What exactly is milk? Depends on whom you ask.

Milk is usually white, brown with chocolate syrup, and occasionally pink. In 2020, that’s where the similarities end.

The dizzying array of milks on local supermarket shelves today comes from very different sources. Pennsylvania dairy cows are in the mix, of course, but so are California almond bushes, Upper Midwest soybeans, and Canadian oats processed in a South Jersey plant by a Swedish-based company founded by a food scientist.

Oatly, a world leader in oat milk production, opened that $15 million plant in Millville, Cumberland County, in 2018 and processes its base product there — oats and water — before adding secret ingredients.

The company is also building a plant in Ogden, Utah, and is in the process of developing U.S.-grown oats.

“Before I started this path to Oatly, I’d never heard of oat milk. I never put those two words together before,” said Mike Messersmith, president of Oatly North America.

Dairy farmers do not think plant-based beverages should be considered milk and have fought, unsuccessfully, to get a hard definition enforced by the U.S. Food and Drug Administration and have those products moved elsewhere in the supermarket.

“There have been a number of federal and state bills where the dairy farmers are saying the legal definition of milk is an excretion of a lactating mammal,” said David Smith, executive director of the Pennsylvania Dairymen’s Association. “For people to be looking for a natural product and go to oat and almond, it just defies logic because they are all built with fortifications and additives. Milk is just natural.”

Oat milk, according to various news reports, is thicker than other plant-based milks and slightly sweeter than dairy, with, of course, a bit of an oat taste. The website Epicurious.com said oat milk is the best alternative to dairy for baking.

The dairy industry was hurting long before the COVID-19 pandemic, with Pennsylvania seeing hundreds of farms close each year or switch to other crops. The state still has 5,730 dairy farms, the second most in the nation, but it has lost more than 1,000 over the last five years. The steepest decline came last year, when 470 dairy farms disappeared.

With schools and restaurants closed during the lockdown, many farmers were left with a glut of supply and were forced to dump milk.

“You work hard to get those cows to produce good quality milk, and then to just spread it on fields," one dairy farmer told The Inquirer in April.

Milk prices rebounded sharply in the summer, up to $20 per hundred pounds from a low of $11 in the spring.

» READ MORE: Can mozzarella help Pennsylvania’s struggling dairy farms? Caputo Bros. Creamery bets on water buffalo.

Messersmith said Oatly was founded in the mid-1990s as an alternative for the lactose intolerant and a more climate-friendly product than dairy. The company entered the U.S. market several years ago by focusing on specialty coffee shops, where soy and almond milk were the dominant alternatives to dairy. A six-pack of 32-ounce “barista edition” Oatly milk retails for $32 on its website.

“We really got great traction early on and while it generated business for us, it also gave people a really positive first experience with oat milk through their local coffee shop and their local barista,” Messersmith said.

Hallie Zimmerman, an assistant manager at Old City Coffee on Church Street in Philadelphia, said oat milk is a standard order today.

“I guess we first started seeing it about a year ago,” Zimmerman said. “It used to be predominantly almond milk, and now it’s oat milk.”

On Wegmans' website, a 64-ounce container is $4.99.

In July 2018, the Food and Drug Administration proposed a rule that would prohibit any manufacturer from labeling a product as milk unless it was “lacteal secretion … obtained by the complete milking of one or more healthy cows.”

“An almond doesn’t lactate,” then-FDA Commissioner Scott Gottlieb said at the time.

The Pennsylvania Farm Bureau also supports enforcement of the strict definition, contending that the current situation creates confusion, “such as believing that ‘almond milk’ is real milk with almond flavoring,” a spokesman said.

Critics of the proposal argue that history has shown a muddled definition of the word “milk” for centuries, and that no single industry can lay claim to it. According to Smithsonian Magazine, almond milk was referenced in medieval Europe.

The FDA sought feedback from the public on the labeling of plant-based products and received 13,000 comments. A spokesman said the agency was considering its next steps. Meanwhile, dairy still shares shelves with plant-based products.

Along with competing against those alternatives, a segment of the dairy industry has also been trying to promote whole milk above milks with lesser fat content, such as skim or 1%. On some rural Pennsylvania roads, “Drink whole milk” or “Drink 97% fat free milk” slogans are affixed to trees or spray-painted on hay bales. The “97 Milk” movement was started by Lebanon County farmer Nelson Troutman in 2019 as a pushback against Michelle Obama’s Healthy, Hunger-Free Kids Act of 2010 that revamped school lunches and cut whole milk from most menus.

Lolly Lesher, a Berks County dairy farmer and board member of 97 Milk LLC, said the former first lady’s program simply resulted in kids drinking much less milk and, in turn, decreasing overall milk sales.

“We’ve lost a whole generation of milk drinkers,” she said.

Way-Har Farm Market, Lesher’s storefront in Bernville, does sell reduced-fat milk, along with chocolate and strawberry. She doesn’t sell plant-based alternatives, though, and believes those products don’t belong on the same shelves as dairy.

“It needs to be on the shelf with juices,” she said.

Oat milk and other plant-based alternatives aren’t going anywhere, a welcome boom for vegans, vegetarians, and people with lactose intolerance. Messersmith said supermarkets are simply responding to consumer demand.

“Cow’s milk, ice cream, and dairy-based yogurts are still far and away the largest owners of that shelf space,” he said. “There’s shifting consumer preference for more plant-based options. People are more cognizant of their choices, how it affects the climate, and it’s shifting how the grocery store works.”