Your “grass-fed” milk may actually not be. But a new technology could change that

To understand why this technique could prove to be transformative, it’s important to first address a simple question: Don’t all cows eat grass? You could be forgiven for thinking so. Anyone who takes a stroll down the dairy aisle at the local supermarket will be confronted by a range of jugs and cartons labeled “grass-fed,” or that feature illustrations of bovines grazing contentedly near the shade of old-timey barns. But the reality behind the marketing is not so simple. Though smaller herds often spend the warmer months outdoors, foraging the grass that makes up most of their diets, the vast majority of American milk comes from cows confined inside large, concrete-floored dairy barns. These cows are fed grass in the form of cut hay, as well as grain silage and crude protein (which can range widely, from soybean meal and day-old bread to red Skittles and chicken feathers). They don’t forage on pasture.

It’s in organic milk where things get tricky—where the matter of what cows eat, once an easy quiz for kindergarteners, becomes a question worthy of the hardest-nosed investigative journalists.

By law, cows that produce organic milk are required to have outdoor access. And not just token access. According to the National Organic Program’s “Access to Pasture” rule, organic dairy cows must spend at least 120 days each year outside; fresh, foraged grass must be a minimum of 30 percent of their diets. But there’s reason to believe that isn’t always happening.

Last May, The Washington Post’s Peter Whoriskey published an exposé alleging serious fraud at an organic dairy north of Greeley, Colorado. The Aurora Dairy’s 15,000-cow herd—huge, considering that the vast majority of organic dairies milk fewer than 100 cows—produces certified organic milk that ends up on shelves at Costco, Safeway, and Walmart, according to the article. But when the Post dropped in on eight different occasions over the course of 2016, something seemed off: Each time, Whoriskey wrote, the fields were empty. Satellite imagery seemed to confirm this account.

For its part, Aurora dismissed the Post’s visits as “drive-bys,” and suggested the cows just happened to be inside when the visits took place. But Whoriskey didn’t rely just on anecdotal evidence: the Post brought receipts. By testing the fats in Aurora’s product, the paper found a nutritional profile that was much closer to conventional milk. That was an important finding because, in general, grass-fed milk tends to be higher in beneficial fats like conjugated lineolic acid and omega-3 fatty acids. Conventional milk is higher in omega-6 fats, which are more abundant in feed grains.

There’s still debate over whether grass-fed milk is healthier, though multiple studies have found that pasture grazing increases good fats in milk (see here and here). But if chemical differences in the milk produced by grass-fed and conventional dairy cattle are so apparent, why can’t the industry apply empirical standards to claims like “certified organic?”

One issue is that gas chromatography—the method of nutritional analysis the Post used to fact-check Aurora’s claims—is too cumbersome and time-consuming to be feasible at scale. It’s also expensive. According to Logan Peterman, an agricultural research manager at Organic Valley, the country’s largest organic dairy cooperative, it can cost as much as $100 per sample, a cost he says is financially prohibitive for most organic dairy farmers and processors.

Which is where the Iowa State study comes in.

Rather than analyze milk’s fat content, the Iowa State scientists used fluorescence spectroscopy—a method that can be thought of as a kind of molecular fingerprinting, one that involves beaming light at the product and measuring for luminescent signals in response. Unlike nutritional testing, which usually requires samples to be sent away to a lab, the results are instantly visible. (Spectroscoptic techniques are already being considered elsewhere in the food industry, including new methods for rapid E. coli detection and spotting fake oregano.)

“Spectroscopy is easy,” says Jacob Petrich, an ISU biochemist who co-authored the study. “There’s really no sample preparation involved. You just need to shine light on the sample, and there are signatures in the milk that you can see. There’s very little preparation to be done, and you get the answer almost immediately.”

Not all foods carry the kind of fluorescent markers spectroscopy can easily measure. But milk happens to contain a strong and readily detectable signal: lingering traces of chlorophyll that have been metabolized by the cow. Think back to freshman year biology—chlorophyll is the green pigment responsible for converting the sun’s light into energy, abundant in grass. When exposed to a certain frequency of light in cow’s milk, it returns a bright, easily detectable cue. This method takes the guesswork out of the grass question, according to the study—the scientists found they could instantly spot the differences between various types of milk.

When the researchers compared milk from a true grass-based dairy to samples from the grocery store, the chlorophyll content varied dramatically. Control samples were taken from Radiance Dairy, a small, pasture-based operation in Fairfield, Iowa, where cows forage 85 percent of their diets from fresh pasture during the grazing season—far more than the 30 percent required by law for organic producers. (Individual brands were anonymized in the study, and the co-authors wouldn’t tell me which specific ones they bought.)

Francis Thicke—Radiance’s owner, who was the Democratic Party’s candidate for Secretary of Agriculture in Iowa in 2010 and just finished serving a term on the National Organic Standards Board—tells me by phone that his cows don’t eat only grass. Given the state of modern cow genetics, he says, the animals do a little bit better with some grain, and that corn is a good way to lure them back into the barn at the end of the day. But his animals do spend the vast majority of their time outdoors, grazing.

And it shows in their milk. The concentration of chlorophyll metabolites in Radiance Dairy milk ranged from 0.13 to 0.11 micromolar, compared to only 0.09 to 0.07 micromolar in a range of organic milk the scientists bought from the supermarket—about 50 percent higher, on average. But the differences were even starker in store-bought conventional milks, which the study found ranged from .04 to a mere .01 micromolar, four to 10 times lower than Radiance Dairy’s milk.

It’s not that these findings have human health implications, in and of themselves. The presence of chlorophyll in milk doesn’t have any specific nutritional benefits that we know about. (Interestingly, the study does point out these higher chlorophyll levels cause grass-fed milk to degrade more quickly in light, an issue easily solved by an everyday cardboard carton.) But the results do seem to establish that spectroscopy can reliably detect how much fresh grass a dairy herd is getting, which may herald the dawn of a new era of transparency in the industry. We as shoppers might not be able to tell how our milk was produced without a Washington Post exposé, but dairy brands could use this method to put more teeth into their process claims.

Mark Rasmussen, a co-author of the paper and the Leopold Center’s executive director, tells me that integrating the method into existing supply chains would likely not be difficult. Commercial milk trucks already conduct quality testing when they pick up product from dairies, he says, and it would be simple enough to fold this process into the existing regimen. The question is whether the industry will be interested in such testing.

One major player already is. When the Leopold Center, one of the nation’s oldest and best-known centers for agro-ecological research, was crippled by targeted funding cuts by the Iowa State legislature last year, much of its in-progress research was put on hold or quashed outright. But a private-sector partner took an interest in this specific area of research and was able to provide some additional financial support—Organic Valley.

Peterman, who helps develop the cooperative’s on-farm standards, tells me that the company has long been interested in testing, but never felt gas chromatography was workable. Yes, it’s burdensome, but the flaw is even more fundamental: chromatography measures nutritional content, and Organic Valley is more interested in highlighting agricultural practices. Research on the human diet and individual fatty acids will continue to evolve, Peterman says, and the company doesn’t want to base its strategy on any one nutritional component. Ultimately, the cooperative believes that the healthiest, most desirable milk comes from cows who graze on grass—and is keenly interested a standard that can measure grass-based practices empirically. Spectroscopy may make that possible for the first time.

The technology has the potential to provide Organic Valley with two tantalizing benefits. First, it could help ensure its own members—2,000 organic dairy farmers across the country, with an average of 72 cows apiece—are providing the pasture time they claim to be. Organic certifiers determine how much grass a herd eats using what’s called the “subtraction method”: farmers keep a log of how much dry matter they feed their animals, and the certifier subtracts that from the total amount of calories the animals would need to stay healthy. Whatever’s left is considered calories taken from the outdoors. Peterman generally has no complaints about this, but acknowledges that it relies on trust and provides only a very general estimate. He thinks spectroscopy would offer an additional data point that would be a useful check against subtraction estimates.

Second, and much more significantly, Organic Valley hopes spectroscopy can bring potential financial benefits. According to Peterman, the cooperative’s cows on average get about 55 percent of their protein from grass during the grazing season—well above the 30 percent standard required by law. Spectroscopy could help create a new premium market, a better-than-organic standard that’s easily verified by science. Organic Valley has already started to market “grassmilk,” a premium product it says comes from 100-percent grass-fed cows who never eat grain. Spectroscopy—with the reassuring presence of hard, fast data—could make it even easier to convince customers of claims like these, and further differentiate such products from more standard offerings in the market.

That could be a major development in the organic dairy industry, where farmers who work hard to do the more logistically difficult, expensive thing—feed a small herd on grass—have not had a clear, reliable way to telegraph that effort to the consumer. Spectroscopy could change that. And it could provide a way for the companies and producers who market grass-fed milk to charge a premium price.

But could the technique be used to combat industrial-scale fraud? Among those who feel the United States Department of Agriculture (USDA) hasn’t done enough to protect the organic standard’s big-business imitators, the Aurora Dairy case is one particularly troubling example of poor oversight. When the Cornucopia Institute, a non-profit organic standards watchdog, filed a formal complaint with USDA regarding the allegations made in the Washington Post article, the agency did perform a follow-up inspection. And though it said it found no evidence of wrongdoing, the circumstances were murky. The agency wouldn’t tell the Post’s Whoriskey if the visit was announced in advance—which critics say could have given the company time to make everything inspection-worthy. 

At the time, Thicke from Radiance Dairy was on the National Organic Standards Board, and was able to ask Betsy Rakola, the National Organic Program’s director of enforcement and compliance, about what happened with Aurora. He says she told him that the visit was in fact pre-arranged, which he feels is evidence of large-scale farms being held to a different standard. But when I reached out to USDA, the agency was unwilling to confirm or deny Thicke’s allegation on the record.

Pre-arranged audits or not, it seems clear that oversight is a sticking point. “We need much better enforcement on this issue,” says Thicke, pointing out that he feels truly organic practices are not possible on such a large scale.

“I don’t think that you can possibly graze 15,000 cows and milk them twice a day,” he says. “It’s biologically, physically impossible to do that—for the cows to go out far enough to get grass and come back. That just can’t be done, because it’d be too far to walk. Besides, they’re on a desert.”

Could spectroscopy help clear up the mystery of Aurora’s alleged misconduct, level the playing field (or grazing field?), and make it easier to tell that organic milk really is organic? Both Peterman and Thicke are optimistic—though they feel strongly that organic is a process certification, one that can’t be boiled down to a mere number, even if some concrete data would be a helpful supplement. And both acknowledged that a scientific test of this kind could give rise to new forms of fraudulent behavior.

“Human ingenuity is incredible,” Peterman says, with a laugh. “And I would say one of the things human beings are the most gifted at is cheating.” He gives the example of an Organic Valley imitator that cropped up near the company’s headquarters in northwest Wisconsin, called Omega Valley—which achieved high levels of Omega-3s in its milk not by grazing cows on pasture but by stuffing them with huge quantities of flaxseed meal. (I couldn’t independently verify this practice, though the Wisconsin Milk Marketing Board mentions that the company had boosted the animals’ omega-3 levels with proprietary feed.)

Thicke says that fraud has always been a part of the dairy industry, pointing out that in the 19th century farmers sometimes bulked up their product by diluting the milk with water. It could be hard to catch someone in the act, and virtually impossible to prove guilt after the fact, though occasionally there were clues: “Some circumstantial evidence is very strong,” wrote the naturalist Henry David Thoreau, “as when you find a trout in the milk.”

For now, the critics of organic standards enforcement have mostly circumstantial evidence to go on. We’ll see whether spectroscopy leads to more transparency across the industry, or simply provides another way to game the system.

Correction: This article initially misidentified the unit of concentration used in the Iowa State study. It is micromolar, not micrometers.