Written by, Polina Raskin.

May 7th 2023

Scientists have always been fascinated by the past, and their studies have helped us to better understand how our ancestors lived. One aspect that has always been of particular interest is the food and drink that was consumed in ancient times. It is through the study of ancient food and drink that we can learn more about the diets of our ancestors, as well as the technologies and techniques that they used to prepare their meals.

In recent years, there has been a growing interest in the study of ancient fermented foods. Fermentation is one of the oldest and most important techniques for preserving and enhancing the flavor of food and drink. In ancient times, fermentation was used to make a wide range of products, from bread and beer to cheese and pickles. In the past, the study of ancient fermented foods has been based mainly on the analysis of organic residue. However, in recent years, scientists have developed new techniques for studying ancient microorganisms, including yeast. One such technique is the isolation of microorganisms from ancient pottery vessels used for fermentation, Taking advantage of their discovery of GASP phenomena in these cells described by the research team.

In a recent study, a team of scientists developed a novel approach to studying ancient fermented foods. The team hypothesized that enriched yeast populations in fermented beverages could have become the dominant species in storage vessels and their descendants could be isolated and studied today. To test their hypothesis, the team developed a pipeline of yeast isolation from clay vessels and screened for yeast cells in beverage-related and non-beverage-related ancient vessels and sediments from several archaeological sites. The team found that yeast cells could be successfully isolated specifically from clay containers of fermented beverages. The findings that genotypically the isolated yeasts are similar to those found in traditional African beverages and phenotypically they grow similar to modern beer-producing yeast strongly suggest that they are descendants of the original fermenting yeast. The team of scientists that conducted the study isolated yeast cells from ancient vessels excavated at archaeological sites in Israel. These vessels belong to vessel types that, based on their shape, or, for example, in the case of the vessel from Ramat Rachel, based on organic residue analysis, were considered to have contained a fermented beverage in the style of  mead (honey wine).

The main challenge of this research lies in the question of whether the isolated yeast strains originated from the ancient yeast that fermented ancient beverages in the archaeological vessels and whether the yeast cells that were discovered are in fact descendants of the original yeasts, having survived and continued to grow in microenvironments in pores within the clay matrix of the vessels. Or, perhaps, they are wild yeast from the environment or a recent contamination.

Several lines of evidence strongly suggest that the yeast strains the team isolated are indeed descendants of fermenting yeasts in the ancient vessels. First, the number of isolated yeast strains from putative beverage vessels (6 out of 21 samples), in comparison with the yeast strains isolated from the control samples (2 out of 110 samples), is significantly biased toward the beverage-related vessels. Second, all yeast strains isolated from the putative beverage vessels besides one grew in beer wort medium, similar to the modern domesticated commercial beer yeast, while all the yeast strains isolated from the control samples show different growth parameters under these conditions.

The observed differences in the number and behavior of yeast strains isolated from putative beverage vessels versus control samples strongly support the hypothesis that the yeast strains are descendants of fermenting yeasts in the ancient vessels. The bias towards beverage-related vessels and the similarity of the yeast strains to modern domesticated beer yeast provide compelling evidence. Moreover, the P-value obtained from statistical analysis was found to be near zero, indicating that the observed differences are highly unlikely to have occurred by chance. Overall, these findings provide strong support for the hypothesis that the yeast strains isolated from the putative beverage vessels are indeed descendants of fermenting yeasts in ancient vessels used for beer fermentation.

The study also sheds light on the domestication of yeast, similar to the domestication of plants and animals. Ancient producers would have used selection processes to domesticate yeast and bacteria that produced “good” and tasty fermented food, much like modern traditional beer-brewing techniques still use today. The findings provide evidence that the isolated yeast strains are descendants of the ancient fermenting yeast, which survived and continued to grow in microenvironments within the clay matrices of the ancient beverage vessels.

The researchers also suggest that large amounts of yeast cells that grew during repeated series of fermentations in these vessels, in antiquity, were absorbed into the nanopores of the vessels. These yeast cells altered the composition of the microorganisms’ population and remained as microcolonies, which continued to grow and survive over millennia in the ceramic matrices of the ancient beverage vessels. This assumption is also based on the observation that yeast cells survived in a clay vessel that was buried for 3 weeks and a clay jug that was exposed to the hot and dry weather of Israel for 2 years.

Moreover, the study's findings might open new avenues in archaeological research, since researchers can expand the isolation of microorganisms from ancient remains, not limited to yeast. It would even be easier to isolate bacteria due to their remarkable survival abilities. This approach can most probably be expanded to a broad range of topics, from disease-borne bacteria to food-associated bacteria, such as those used in fermented beverages, cheese, and pickles.

As final thoughts I will leave you with this, the study of ancient fermented foods using modern microorganisms provides a one of a kind insight into our ancestral diets and the techniques used for food preparation. The findings of this study also have significant implications for the food & beverage industry and the hobby market. By exploring the domestication of yeast and other microorganisms used in fermentation, researchers and enthusiasts can gain a better understanding of how to optimize the fermentation process and create new and unique flavors. This can lead to the development of new and innovative products for the food and beverage industry, as well as the creation of new hobbyist communities interested in exploring the world of ancient fermented foods. So, let's continue to explore the world of fermentation, learn from our ancestors, and develop new and exciting ways to enjoy the flavors and benefits of fermented foods.