Scientists found yeast in frozen mother's intestines, and used it to make sourdough bread

Yeast has been growing in the intestines of the so-called frozen mother Oetzi the Iceman thousands of years, scientists have discovered, telling AFP that they used it to make sourdough bread.

More than 5,300 years ago – before the construction of the pyramids of Egypt – Oetzi was hiking in the Alps on the border of Austria and Italy when he was killed by an arrow in the back.

He remained frozen in the snow until two German climbers came across his embalmed remains in 1991 in the northern Italian region of South Tyrol.

Since then, his incredibly well-preserved remains have been kept at the same temperature – below six degrees Celsius – as his frozen tomb.

This has allowed scientists to carefully study Oetzi, providing an incredibly rare window into the life of ancient man.

In a recent study, published in the journal Microbiome on Wednesday, an Italian-based team found evidence that ancient and modern microbes remain active in a frozen body.

“What we didn't expect to find was yeast,” study lead author Mohamed Sarhan of Eurac Research in the Italian city of Bolzano told AFP.

“His body contains organisms with metabolic adaptations that actively respond to their environment,” Sarhan told Reuters news agency. “The yeast associated with the cold grows. Certain bacteria accumulate and persist in all her tissues for decades. The mother, in the true sense, is a living interface of organisms – a meeting place between the ancient and modern world, where bacteria from 5,000 years ago live with animals that arrived ten years ago.”

“Very good dough”

Scientists found four different sub-zero yeasts in Oetzi's intestines, skin and the “brown” water that melts in his body when it is not partially frozen.

These types of yeast only live in very cold conditions like Antarctica, so it is believed that they entered Oetzi's body sometime after his death.

Genetic analysis revealed “levels of DNA damage very comparable to the original bacteria” in the Iceman's gut, suggesting the yeast entered his body shortly after death, Sarhan said.

“This yeast accompanied Oetzi on his long journey through the millennium,” study co-author Frank Maixner said in a statement.

The scientists then produced intestinal yeast in the refrigerator.

If you tell anyone that you have yeast, they immediately ask: Can we use it for bread? Sarhan said.

So they tried to make sourdough bread.

“At first it didn't work,” admitted the biologist.

But after three months of effort “we had a really good sourdough,” Sarhan said with a laugh.

When asked if scientists were considering using yeast to make beer, he replied: “It's on the list.”

The study contained the possible serious use of yeast.

When the mother was found in 1991, she was initially treated as a normal cadaver. A chemical called phenol was used to prevent fungus from growing in the body.

However, a strange yeast has been able to eat phenol, which means that in the future it could help break down the chemical in polluted areas, scientists say.

Inside the ancient microbiome

Yeast wasn't the only surprise found in Oetzi's body.

Analysis of his microbiome revealed a type of gut bacteria that is virtually absent among modern humans.

Although it no longer exists in the stomachs of people in the industrialized world, the bacteria have been found in African and South American tribes, said Sarhan.

It was also found in 3,000-year-old feces stored in a salt mine in Hallstatt, Austria – serving as one of the first insights into the ancient human microbiome.

Oetzi and these Bronze Age salt miners ate more fiber and grains than modern humans, Sarhan explained.

The study, published in the journal Microbiome, said it “reveals that the Iceman is not a 'frozen' time capsule but a complex ecosystem.”

A previous study revealed that Oetzi's last diet included venison and goat meat as well as wheat, Reuters reported. Previous research has shown that he was about 45 years old at the time of his death and in good physical condition, carrying a bronze axe, a longbow, arrows and a quiver and a bow.

“He is a visitor who gives us valuable insights into the past,” Maixner told Reuters.

It's too early to tell if yeast harms the mother, Sarhan said, calling for more research.

Nikolai Oskolkov, a researcher at the Latvian Institute of Organic Synthesis who was not involved in the study, told AFP it was interesting that “the Iceman's microbiome is not 'frozen'”.

However, Oskolkov, who found ancient fungi in the intestines of mothers, warned that yeast samples were taken only in 2010 and 2019.

This provides “little evidence that the yeast has been multiplying for thousands of years,” he said, adding that he believes they were “recent colonists in the mother's body.”

In 2023, scientists discovered that Oetzi was more of a peasant descent from present-day Turkey, and that his head was bald and his skin was darker than originally thought.