Ancient DNA reveals make-up of Roman Empire’s favourite sauce

The fermented fish sauce, or Garum, was an incredibly popular condiment throughout the Roman Empire. For the first time, the old DNA – scraped from the tanks used to produce the sauce – revealed exactly what fish species entered the culinary clip.

The Roman fish sauce was appreciated for its savory flavors and Umami – although the philosopher Seneca described a version like “the guts too expensive of rotten fish”. It came in several forms, including a liquid sauce called Garum or liqueur, as well as a solid paste known as Allec. To prepare the condiment, crushed fish rhythm plants and fermented fish, a process that can make visual identification of the species difficult or impossible.

“Beyond the fact that the bones are extremely small and fractured, old age and acid conditions all contribute to the deterioration of DNA,” explains Paula Campos at the University of Porto in Portugal.

Campos and his colleagues carried out DNA sequencing tests on bone samples about the 3rd century AD, extracts from a Roman plant of fish rhythm in the northwest of Spain. They were able to compare multiple DNA sequences that overlap and associate them with a complete fish genome, giving the team “more confidence than we identify the right species”, explains Campos.

The effort has identified the leftovers of fish as European sardines – an observation that aligns with the previous visual identification of sardine remains in other plants of fish rhythm in the Roman era. Other Garum production sites have also contained the leftovers of additional fish species such as herring, merlan, mackerel and anchovies.

This proof that “degraded fish remains” can produce identifiable DNA “could help to identify with more precision certain regional variations in the main ingredients of the old sauces and fish pasta,” explains Analisa Marzano at the University of Bologna in Italy, which did not participate in the study.

The study also compared the DNA of ancient and modern sardines to show that there was less genetic mixture of sardine populations of different oceanic regions in ancient times. This insight could help “assess the effects of human interaction-environment over the centuries”, explains Marzano.

For their next step, Campos and his colleagues plan to analyze other species of fish from Garum production sites in the Roman era. “We expand the sampling locations to see if the results are consistent throughout the Roman Empire,” she says.