SAN FRANCISCO — No one can even agree on milk anymore.

What is it? Where does it come from? Must it be lactated?

This seemingly existential debate is now pitting the dairy industry against the makers of what are known as “alternative milks” and neighborhood baristas. It was set off most recently by the commissioner of the Food and Drug Administration, Dr. Scott Gottlieb, when he made a surprising remark in July at a panel discussion in Washington.

“An almond,” he said casually at the end of the event, “doesn’t lactate.”

With his comment, Gottlieb plunged into the tensions over alternative milks — the plant-based beverages made from macadamias, almonds, quinoa, peas, rice, coconut, oats, soy, walnuts or cashews. A growing number of Americans are embracing these milks, made through maceration and sometimes fermentation, at their neighborhood coffee shops and at home.

New milks come on the scene fast, a Cambrian explosion of varietals, and alt-milk trends tear through communities: New Yorkers recently experienced an oat milk shortage.

Consumption of these plant-based beverages has risen rapidly, jumping 9 percent to $1.6 billion in the 12 months through June. In the same period, sales of cow’s milk fell 6 percent, according to data from Nielsen and the Plant Based Foods Association. Milk drinking, meanwhile, is on the decline. In the 1970s, a typical American drank about 30 gallons a year, but now it’s about 18 gallons, according to the Department of Agriculture.

All of this worries the dairy industry.

“You don’t got milk if it comes from a nut or a seed or a grain or a weed,” said Chris Galen, a vice president at the National Milk Producers Federation, which was established in 1916 to advance the well-being of dairy producers. He was repeating one of the dairy industry’s new phrases: “You don’t got milk if.”

His group is pushing for the Dairy Pride Act, introduced in Congress in January 2017, which he said would compel the Food and Drug Administration to enforce its rules around labeling things honestly. The dairy industry argues that the word “milk” confuses consumers because it implies that the white liquid they have bought has a nutritional value similar to cow’s milk.

Michele Simon, executive director of the Plant Based Foods Association, acknowledged that an almond may not lactate, but “it doesn’t mean you can’t call it milk.” She said people knew perfectly well when they bought soy milk that it was not the same as animal milk. Alt-milks often do not have the same fat, protein and vitamin content as dairy milk.

A study the association commissioned last year found that 2 in 3 consumers agreed that the best name was the plant ingredient followed by “milk,” Simon said.

“No one owns the English language, and we’re not backing down,” she said, adding that she hoped this could all be resolved “in a peaceful manner.” She said she had recently ordered a shirt with the phrase “an almond doesn’t lactate” on the front, which she plans to wear to the local farmers market.

Nut juice or almond beverage?

With the dairy industry and the plant-based foods group at such odds, Gottlieb’s comment about almonds and lactating immediately caused a panic. It was the strongest indication yet that his agency would begin more fiercely enforcing rules for milk labels.

“These products can vary widely in their nutritional content — for instance in relation to inherent protein or in added vitamin content — when compared to traditional milk,” Gottlieb wrote in a statement about a week later. He added that he would be “modernizing our standards of identity” for dairy products.

The Food and Drug Administration declined a request for comment.

For fans of alt-milks, Gottlieb’s remarks have prompted questions. If the plant-based concoctions are not milks, would people drink something called nut juice? Or almond beverage?

In Brooklyn’s Williamsburg neighborhood, the owner of Cafe Beit, Jon Reagan, who sells homemade almond milk, said he was prepared for jail time over the issue.

“I mean, what would happen if we did call it milk still?” asked Reagan, 31, shifting to a fake newscaster voice: “The owner of Cafe Beit was sentenced to 10 years.” He said that he thought it was “stupid to have a law” and that it was “just because the milk industry’s afraid.”

Greg Steltenpohl, a co-founder and the chief executive of Califia Farms, which makes almond milk, argued that the latest debate was overblown. He pointed out that the Department of Agriculture found last year that 90 percent of households that bought alt-milks also purchased dairy milk.

“The real world is less polarized than the politics make it out to be,” he said.