Humans have been drinking beer for thousands of years nowJustin Sullivan/Getty Images

The oldest-ever confirmed evidence of beer has been found by archaeologists in cups near what was once the ancient city of Mesopotamia. The cups show that people were regularly brewing and chugging beer over 2,500 years ago.

Archaeologists have long known that there are several factors that pointed to ancient humans brewing and drinking fermented alcohol. It was quite an important part of life in the ancient world, notes a report by the Smithsonian. Researchers have only found actual evidence of beer as residue in 2,500 years old clay cups in a dig site near Northern Iraq. Not only the residue, there was a conclusive evidence of fermentation as well.

The research team has demonstrated that the chemical signature of fermentation in the vessels is also consistent with barley, says Claudia Glatz of the University of Glasgow and co-author of the study. "Putting those together is the interpretation that this is barley beer."

This same technique could likely be used to find beer and alcohol in other dig sites around the world as well, notes the report. "[Beer] is a quintessential Mesopotamian food stuff," says Glatz. "Everyone drank it but it also has a social significance in ritual practices. It really defines Mesopotamian identities in many ways."

While this is the first time that actual physical evidence of beer has been found, there have been several hints that beer was brewed during the Mesopotamian age when a 4,000 years old brewery was found though it was not as conclusive as this dig. The report mentions that there was a "beer stone"—fermented barley compounds.

There was a need for beer in ancient times because fermentation was one way to keep barley safe to consume for long and even made it more nutritional. Also, beer is fun to drink.

Now, Perruchini and Claudia Glatz are trying recreate the recipe using the residue they found. "It smells so terrible," Perruchini told Smithsonian.

The study was first published in the Journal of Archaeological Science.