How do you like your milk: cooked or raw? It may sound an odd question, but it’s being asked more often at kitchen tables, grocery stores and farmers’ markets across the US.

The vast majority of milk we drink is pasteurized – heat-treated to kill off harmful pathogens. Raw milk, on the other hand, goes straight from udder to bottle. Fans call it milk as nature intended: nutrient-rich and full of probiotics, the good kind of bacteria. Some fans go further, calling it a superfood that aids digestion, boosts the immune system and treats asthma, eczema and allergies.

For blogger and cookbook writer Jennifer McGruther, trying raw milk several years ago was a natural extension of her interest in traditional diets and locally made food. But in Colorado, where she lived at the time, you couldn’t just go to the store and buy it. In fact, due to concerns about safety, retail sales of raw milk are prohibited in about 20 states. So she joined something called a “herd-share” scheme, which lets people buy an “interest” in a group of dairy cows. “As a part-owner, you’re entitled to what that cow produces,” she explains. “It’s difficult for the state to say you can’t drink the milk from cows you own.”

McGruther loved the taste and so did her family. Before long, she says, her four-year-old son would burst into tears if she gave him regular milk. “There is this richness to it, and it tastes different based on the seasons,” she says. “There is a uniformity that comes with pasteurization, but food is not uniform.”

Inside the milking barn at Organic Pastures raw dairy farm in Fresno, California. Photograph: Charlotte Simmonds/The Guardian

An increasing number of people agree. For health-conscious, organic-loving shoppers, raw milk is a growing food fad. Who wouldn’t feel saddened by the thought of heat-blasted, barren milk sitting under supermarket strip-lighting when the alternative is painted as a living food, fresh and full of character? Goop recently caused a stir by featuring a naturopathic doctor who recommends an eight-day raw goat’s milk cleanse to rid your body of parasites; some swear by it, others swear it will just make you fart. But when Gwyneth Paltrow jumps on the bandwagon, you know a food is having a moment.

McGruther agrees that raw milk is a much bigger deal than it was 10 years ago. She says many of her 500,000-plus readers come to her blog, The Nourished Kitchen, specifically to find out more about it. The US government estimates that 3.2% of people now drink it, though advocates I spoke with suggest the figure is more like 5%.

But despite the enthusiasm, it’s a trend with an unsavory side. Pasteurization is the norm for a reason – it’s highly effective at killing things such as E coli, salmonella, campylobacter and listeria that can hang around in the gut and feces of even healthy cows. Raw milk, on the other hand, relies heavily on the skill of the farmer and the cleanliness of the operation to avoid contamination.

A US food safety official once compared drinking raw milk to “playing Russian roulette”, and a study published by the Centers for Disease Control and Prevention (CDC) says raw milk illnesses have spiked as more people drink it. Between 2009 and 2014, raw milk and raw milk cheese caused the vast majority (96%) of all illnesses linked to contaminated dairy products. Considering far fewer people consume it, that makes unpasteurized dairy 840 times more risky than pasteurized, the study says. The recent deaths of two people who ate raw milk cheese made in New York underscored the sometimes deadly consequences.

Eight years ago, Michele Jay-Russell, a microbiologist at the University of California at Davis, helped start a website called Real Raw Milk Facts to counter what she describes as a “very sophisticated misinformation campaign” lauding the benefits and downplaying the dangers.

Organic Pastures raw dairy farm in Fresno, California. Photograph: Charlotte Simmonds/The Guardian

She says several European studies and observations of Amish farm children do suggest those who drink raw milk have less asthma and fewer allergies. But the science is not clear-cut, she adds, and questions remain about whether other factors of farm life – proximity to animals, diet, spending time outdoors – could have swayed results.

And for young children, whose underdeveloped immune systems make them more vulnerable, the dangers of raw milk make it hard to recommend. “For an adult it’s not really worse than eating raw oysters or sprouts,” she explains. “But I would say it’s one of the most risky foods you could give a child under five.”

•••

Mark McAfee, founder of Organic Pastures, the nation’s largest raw milk dairy farm, would disagree. He’s been producing and bottling raw milk in Fresno, California, for 17 years. “Yes, raw milk can be risky,” he says. “But I can make a very good argument that it’s safer than pasteurized milk if produced expressly for human consumption.”

McAfee’s passion puts him at the forefront of the pro-raw movement. He’s a gregarious dairyman – a fast talker who rattles off the benefits while steering his truck one-handed as we ride toward the milking barn. He is eager to demonstrate how sanitary the operation is. Milk is pumped straight from the cow into super-chilled cisterns. There it’s held for 24 hours while samples are sent to be tested for E coli and other harmful bacteria.

Business is booming, he says, with annual sales at $12m and growing and some 80,000 people drinking his milk in California, including celebrity fan Martin Sheen.

Actor Martin Sheen and supporters attend a press conference for the Fresh Raw Milk Act at Whole Foods in Venice, California, in 2008. Photograph: Chris Wolf/FilmMagic

At the farm I get chatting with Maggie and Dana Troutman, raw milk drinkers from San Diego. Maggie says she was raised on the stuff and claims her family has no history of disease as a result. “When I’m traveling and I can’t get my raw milk, I notice a difference in two days,” she says. “I don’t feel strong. It’s like my cells are starving.”

But Organic Pastures has had its growing pains. Their milk has been linked to multiple outbreaks, including an E coli outbreak in 2006 that left several children hospitalized. One of those children was seven-year-old Chris Martin, who developed acute kidney failure that almost killed him.

Chris’s mother, Mary McGonigle-Martin, told me she “didn’t grow up eating healthy” but was drawn to raw milk because she had heard it was more nutritious. “I thought it was supposed to be good for you. I was lulled into a false sense of security.”

McGonigle-Martin’s story highlights just how personal, and at times contentious, the debate has become. The raw milk movement is, after all, fighting against a significant advancement in food safety that’s credited with saving millions of lives. In the early 20th century – before pasteurization became widespread in the US – one in four foodborne illnesses were caused by milk. Today it’s less than 1%.

But for those who love it, drinking raw milk isn’t just about the taste or supposed health-giving effects – it’s about a return to a pre-industrialized past, a rejection of mass production, a middle finger to the government for restricting food choices. (It’s legal to buy plenty of other things that kill you, after all, from cigarettes to soda.)

“When I speak to my students now, they are far more concerned about things like antibiotics, GMOs, pesticides and hormones in their food,” says Jay-Russell, the microbiologist. “They think they’re avoiding the horrors of industrialized, processed food.

“But,” she adds, “people have forgotten that sometimes there was a reason for those processes in the first place.”