In Finland, people once put live frogs in milk to keep it fresh; the science behind this strange tradition |

It’s hard to imagine a frog in your milk container. But not in Finland! This might sound like a bizarre folk tale, but this unusual practice was reportedly followed by rural communities in Finland and Russia long before refrigerators were introduced. Back in time, people would place a live frog in a vessel of milk and allow it to help delay spoilage. While the practice might seem unhygienic and extremely shocking, scientists have discovered a fascinating connection between this traditional belief and the natural defence mechanisms of amphibians.Curious case of frog and milkBefore refrigerators became a household thing, keeping milk fresh was a challenge for farming communities. Fresh milk could spoil quickly, particularly during warmer weather. So in rural communities, people relied on several traditional methods to extend the usability of perishable foods.One of the most unusual reported practices was placing a live frog in a vessel of milk. The custom was associated with northern Russia and Finland, where the Russian brown frog, scientifically known as Rana temporaria, was linked to the belief that milk could be kept from turning sour for longer.A 2013 research paper published in the Journal of Ethnobiology and Ethnomedicine, examining traditional Sami healing practices documented by Johan Turi, refers to reports of people in northern Russia and Finland putting frogs into milk containers to delay souring.The surprising scienceThe most fascinating part of this story emerged when scientists began investigating the reason behind such a strange tradition.Frogs live in environments where they encounter numerous bacteria, fungi and other microorganisms. Their skin plays an important role in protecting them against some of these potential threats. According to research published in the scientific literature, these compounds can act against particular bacteria and fungi. Their activity varies depending on the frog species, the peptide involved and the microorganism being tested.Why this unusual tradition matters today

Frog in the milk vessel (Canva)

People living in earlier times did not have access to modern laboratories or microbiological testing. Their understanding of the natural world developed through observation, experimentation and knowledge passed between generations.For travellers interested in Finland, it is an addition to an unusual dimension to the country’s rural past and its relationship with nature. Beyond its forests, lakes and northern landscapes, Finland’s traditional way of life offers plenty of opportunities to explore how communities adapted to their surroundings.The next time you come across a story about an extraordinary old-world custom, remember that folklore and science can sometimes intersect in unexpected ways.Sometimes, the most surprising stories from the past reveal how closely human life has always been connected to the natural world.