At one of the world’s most unconventional restaurants, almost nothing surprises diners. At Copenhagen’s acclaimed Alchemist, the menu already includes beeswax-aged pigeon, roasted mealworms and dishes designed to challenge every expectation of fine dining. So when the restaurant’s chefs began experimenting with an old Bulgarian recipe for yogurt that required dropping live ants into warm milk, it barely raised an eyebrow. For microbiologist Leonie Jahn, however, it raised something far more valuable. Questions. “I wanted to know what the ants were actually doing,” said Jahn, a senior researcher at the Technical University of Denmark. “Was it the acidity? The bacteria? Something else entirely?” Those questions sparked an unusual scientific investigation, the results of which were recently published in the journal iScience. The research began far from Denmark, in the mountains of Bulgaria. Anthropologist Sevgi Mutlu Sirakova grew up in the small village of Nova Mahala, where homemade yogurt has long been part of daily life. While documenting local food traditions for her graduate research, she interviewed elderly residents about the methods their families had used for generations. Many recipes involved natural ingredients such as spring rainwater and plant roots. Then her grandmother mentioned something unexpected. “We used ants,” she told her. The comment transformed a cultural memory into a scientific mystery. Curious researchers soon travelled to the village to recreate the forgotten technique with guidance from Sirakova’s family. The process was surprisingly simple. Four red wood ants were placed into warm milk inside a small container. The container was sealed, buried inside an active anthill and left overnight. When researchers uncovered it the following day, the milk had already begun thickening. After removing the ants, they tasted the mixture. According to the research team, the yogurt carried a gentle tang with fresh herbal notes and the rich flavour often associated with grass-fed dairy. Back in the laboratory, the bigger mystery remained. Why had the milk fermented? Chemical analysis revealed that the ants contribute far more than their physical presence. Wood ants naturally produce formic acid as a defence against predators. At the same time, bacteria living inside their digestive systems release lactic acid and acetic acid, two compounds already familiar in traditional dairy fermentation. Together, these acids and naturally occurring enzymes trigger the transformation of milk into yogurt. Even more surprising, once the first batch has fermented, it serves as a starter culture for future batches. No additional ants are needed. Food historian Paul Kindstedt, professor emeritus at the University of Vermont, believes the discovery opens an entirely new area of research. “This sequence of fermentation is unlike anything we’ve seen in dairy science,” he said. “There is still much to understand.” Beyond its scientific curiosity, the discovery carries cultural importance. Sirakova sees the research as a way of preserving knowledge that was quietly disappearing from her community. Traditional fermentation methods often create unique combinations of beneficial bacteria that modern industrial food production no longer provides. Those microbial communities help support digestion, strengthen immune function and contribute to overall gut health. Protecting that diversity, she argues, is as valuable as preserving old recipes themselves. That does not mean ant yogurt will soon appear on supermarket shelves. Researchers stress that wild ants may carry harmful parasites or other microorganisms capable of causing disease. For that reason, scientists strongly advise against attempting the recipe at home. Instead, the study offers something far more lasting than an unusual meal. It reminds us that some of humanity’s oldest culinary traditions still hold scientific secrets waiting to be uncovered. Sometimes, the smallest creatures leave the biggest discoveries behind.