Oat Milk as the House Pour: Study Shows Default Choice Can Shrink Latte Emissions by a Third

Almost any café will list oat or soy among its milk choices, yet alternative milks often cost extra or must be specifically requested. Dairy milk, by contrast, carries a far heavier carbon burden than plant-based options.

So what changes when a café flips the arrangement and serves oat milk as its standard pour? According to a study published in Global Environmental Psychology, such a switch can cut a latte's carbon footprint by as much as 34%.

The research was carried out at a university café in the U.K., where oat milk became the default and customers wanting dairy had to ask for it. Signs posted in the café explained the change and cited environmental reasons. A second campus café kept dairy as its default and served as a control.

The work centers on the "default nudge"—the notion that most people stick with whichever option is preselected. Researchers used an ABAB design with four stages: baseline, intervention, a return to baseline, and a second intervention. This structure let them assess the effect more reliably, since it produced two separate sets of measurable results over a longer period and with more participants.

In the first baseline stage, with dairy as the default, 16.6% of customers chose oat milk. Once oat milk became the default in the first intervention, that figure rose to 51.9%. Dairy was then restored as the default for the second baseline stage, and oat milk consumption dropped to 23%.

When oat milk again became the default in the second intervention, the share choosing it climbed back to 46%. Although that was still high, the authors propose that the somewhat lower figure points to a need for further research into how the nudge performs over the longer term. The control café showed no change in oat milk use across the same period.

"We found that customers were approximately three times more likely to consume plant-based milk when oat milk was the default milk option instead of dairy milk and that the mean milk-based carbon footprint per drink reduced by 25%–34%," the authors wrote in their conclusion. "These findings suggest that default nudges can help encourage plant-based diets among consumers by reducing dairy consumption and enhancing sustainable plant-based milk consumption."

Milk accounts for a substantial share of a café's carbon footprint—Starbucks describes it as a "key contributor" to the coffee giant's overall impact. A 2025 study found that milk was responsible for more than 75% of a latte's carbon footprint. Some coffee companies, Blue Bottle and Stumptown among them, have already made oat milk their default in cafés as a way to lower emissions.

"We hope by providing more people with the experience of oat milk we might inspire guests to choose it more often both at our cafes and at home, so together we can reduce our greenhouse gas footprint from dairy," Blue Bottle stated in a blog post explaining the move.

Photo by Clay Banks on Unsplash