Beer has been around for centuries—lots of world cultures have developed some variation on fermented grain and water. But the brews our distant forefathers drank were probably a lot different than the ones we drink now.

While the ale that was enjoyed centuries before the birth of Julius Caesar may have been tastier than other beverage choices of the day, it was still incredibly sour, with a flavor closer to vinegar than Hefeweizen. That’s according to a team of University of Chicago archaeologists and brewers from the Great Lakes Brewing Company. Using a 5,000-year-old beer recipe outlined in “Hymn to Ninkasi,” an ode to the Sumerian goddess of beer, they brewed up a batch of era-appropriate beer. To help ensure authenticity, they even used recreations of ancient wooden tools and ceramic fermentation pots based on artifacts found in Iraq in the 1930s, malted the barley on a roof, and hired a baker in Cleveland to prepare the bappir (“beer bread”) they used as the source of their yeast. And they heated the beer during the brewing process the old fashioned way: over a manure-fueled fire.

Much like Mesopotamian brewers, the crew also didn’t use any modern-day cleaning methods to get rid of the naturally occurring bacteria in the pots. After letting their strange brew ferment for two days, they finally tasted it and deemed it too sour for the 21st century. Nate Gibbon, a Great Lakes brewer who spent a few months doing prep work for the project, isn’t tossing in the towel though. He’s vowed to give the 5000-year-old beer recipe another try, hopefully marketing the ancient beer through Great Lakes some day, but next time he’ll sweeten the beer with honey or dates, as his successors may have done back in the day to make their products more drinkable.