For 16 days, locals and tourists gather every year in Munich, Germany for Oktoberfest, a celebration with plenty of beer and local food. A group of scientists analyzed the methane emissions of the celebration and it turned out it’s not a very climate-friendly event.

The researchers from the Technical University in Munich walked and cycled around the perimeter of the festival last year with mobile sensors aloft. The results showed the event emitted nearly 1,500kg of methane, which is 10 times the amount that wafted off Boston, Massachusetts, in the same period.

Most of the emissions can be linked to leaks and incomplete combustion in cooking and heating appliances, the experts said. At the same time, about 10% of the rise in the gas was attributed to the flatulence and burps of attendees.

“The observed methane concentrations cannot solely be explained by biogenic sources,” Jia Chen, who studies greenhouse gases in urban environments, told The Guardian. “We have strong indications that fossil fuel methane emissions by gas grills and heating appliances are major sources.”

Methane is the second most common greenhouse gas emitted by human activity, following carbon dioxide. It accounts for about 20% of global heating due to anthropogenic greenhouse gas emissions since 1750. Atmospheric levels of the gas have surged in recent years.

Chen and the group of researchers had noticed an increase in Munich’s methane levels during Oktoberfest in previous years, so they decided to monitor the event. More than six million people visit Oktoberfest each year and make their way through more than seven million liters of beer, 100,000 liters of wine, half a million chickens and a quarter of a million sausages.

On average, every square meter of Oktoberfest in 2018 released 6.7 micrograms of methane per second. Less than 10% was calculated to come from festivalgoers in the form of flatulence and burps, according to a paper submitted to the journal Atmospheric Chemistry and Physics.

The work done by the researchers could now help festival organizers draw up policies to reduce their methane emissions. The study concludes the releases of methane are high enough for major festivals to be considered greenhouse gas sources in local emissions inventories.

“Large but time-limited festivals, like Oktoberfest, are sources that have not been accounted for in existing emission inventories, even though, as we have seen, the methane emissions are significant,” Chen said. “Inaccurate or incomplete emission inventories are a problem because many decisions are based on this data.”