people often “preserved” milk not by cooling it in a box but
They would put European brown frogs, or Rana temporaria, in a bucket of milk. All they knew was that it would keep their milk from going sour.
It may seem strange to us, but it was an effective practice.
Unlike poisonous or psychedelic amphibians in the wild, Rana temporaria is a treasure trove of powerful antibiotic substances.
Today, scientists are researching the
germicidal properties of Rana temporaria’s skin, uncovering a rich arsenal of bioactive compounds that go beyond milk’s protection.
Later, scientists discovered that the frogs’ skin secretes antimicrobial compounds, which help prevent the growth of bacteria in milk.
It might sound a bit odd today, but in parts of Russia and Finland – before modern refrigerators were around – people often “preserved” milk not by cooling it in a box but by letting it naturally ferment into a more long‐lasting product. In many cases the milk wasn’t stored in a “modern” container at all but was placed in vessels whose very nature helped kickstart fermentation.
For example, in some traditional practices milk was put into containers made from animal stomachs. The inner lining of a cow’s (or reindeer’s) stomach contains natural enzymes (like rennet) that begin to curdle and ferment the milk. In effect, the milk would slowly sour, transforming into products such as a kind of sour milk or proto–kefir. This souring not only changed the flavor but also made the milk less hospitable to spoilage‐causing bacteria, allowing it to be kept safely for longer.
In other cases, people might have used wooden or birch bark–lined containers. Such materials sometimes harbored beneficial bacteria that would encourage fermentation in a controlled way. The end result was a dairy product that was safer to drink and easier to store until fresh milk could be obtained again.
So while we now think of refrigeration as the obvious way to “preserve” milk, these traditional methods relied on fermentation – a technique as old as dairying itself – and clever use of locally available materials to keep milk edible in harsh climates long before electric coolers became common.