Two forgotten bottles in a basement in Frederiksberg containing bacterial cultures from the 1890s have provided researchers at the University of Copenhagen with unique insight into Denmark's butter production history. Using advanced DNA analysis, they have examined the contents of the bottles, which offered several bacterial surprises and a reminder of the challenges of hygiene at the time.
You eat billions of them in your cold soup, yogurt, sausage, and cheese. Lactic acid bacteria have long been used to flavor our food and extend its shelf life by acidifying it and displacing harmful bacteria. In fact, Denmark was among the first to use the magic of lactic acid bacteria industrially, which, together with the introduction of pasteurization, helped to ensure the high quality of dairy products and, not least, keep them free of disease.
This is evidenced by the discovery of two bottles of white powder, which researchers from the University of Copenhagen found by chance in a dusty moving box last year. The bottles had labels indicating that they contained cultures consisting of lactic acid bacteria, but had not seen the light of day since the late 1800s and were well hidden away in a basement under the greenhouses on Rolighedsvej near the old Agricultural College in Frederiksberg.
Now, using advanced DNA sequencing, researchers have examined the powder in the bottles more closely and compared the DNA with various databases of known bacteria. This was something they were not at all sure was possible, because all organic material decays over time.
The powder did indeed contain the remains of the lactic acid bacteria that Danish dairies used to buy and add to cheese, milk, and butter after the products had been pasteurized to kill unwanted bacteria.
"It was like opening a kind of microbiological relic. The fact that we were able to extract genetic information from bacteria used in Danish butter production 130 years ago was far more than we had dared to hope for," says microbiologist Jørgen Leisner from the Department of Veterinary and Animal Sciences.
Hygiene conditions were different
In the bottles, the researchers found DNA from Lactococcus cremoris-a lactic acid bacterium that is still used to acidify milk in modern dairy production. The analysis also revealed that the bacterial culture had genes to produce diacetyl-a flavor compound that gives a characteristic butter aroma.
"This shows that even back then, they had bacteria with precisely the properties that are desirable in the fermented milk products we have today," says Professor Dennis Sandris Nielsen from the Department of Food Science.
On a more serious note, the analyses also showed that the bottles were heavily contaminated with Cutibacterium acnes - a common skin bacterium known to cause acne.
"The acne bacterium has a stronger cell wall than many other bacteria, as it needs to be able to survive a hostile environment on the skin. Therefore, it also breaks down more slowly, which enabled us to find its DNA in large quantities after 130 years in the bottles," explains Jørgen Leisner.
In addition, the bottles also contained DNA traces of potentially pathogenic bacteria, including the staphylococcus bacterium, Staphylococcus aureus, and Vibrio furnissii. The latter is known to cause stomach infections when eating shellfish that has not been cooked properly.
"Overall, the contents of the bottles testify to the standardization of a dairy product that every farming family used to make themselves in a jar of sour milk kept close to the stove. But it also shows that hygiene conditions were still different from those we have today," says anthropologist Nathalia Brichet from the Department of Veterinary and Animal Sciences, who is co-author of the study.
Unique insight into Denmark's butter adventure
At the end of the 19th century, Denmark began exporting butter to England on a large scale. This placed new demands on consistency and hygiene in production. And here, pasteurization became the solution. But because heat treatment also kills natural bacteria, there was a need to add bacterial cultures-also called starter cultures-and thus began Denmark's industrial adventure.
"The starter culture became the key to standardized butter production. It was no longer possible for each dairy to ferment in its own way-it was necessary to ensure that the products tasted the same, regardless of where in the country the butter was made. The starter culture made the taste reproducible," explains Jørgen Leisner.
The discovery also shows how close collaboration between researchers, industry, and agriculture laid the foundation for Danish food exports. Companies such as Blauenfeldt & Tvede and Christian Hansen emerged during this period and laid the foundation for today's food giants.
"It's easy to forget the enormous scientific work it takes-and took-to produce standardized, food-safe, and sought-after dairy products for export. This didn't just happen by itself, but is the result of technological advances and innovation dating back a long time. This research gives us an insight into a time when Danish dairy production became a global commodity," concludes Nathalia Brichet.
The study was conducted in collaboration between the Department of Food Science and the Department of Veterinary and Animal Sciences.
