Why would scientists revive a thousand-year-old medical recipe for a foul-smelling concoction? They suspected it could have a very real benefit, and it turns out they were right. An Anglo-Saxon brew kills methicillin-resistant Staphylococcus aureus, or MRSA, scientists from the U.K. have announced.

When microbiologist Freya Harrison chatted with Christina Lee, an Anglo-Saxon scholar, she was intrigued by a nasty-sounding recipe in Bald’s Leechbook, a thousand-year-old compendium of medical advice and potions. Here’s the recipe, which was recommended to fight infected eyelash follicles (styes):

Take cropleek and garlic, of both equal quantities, pound them well together… take wine and bullocks gall, mix with the leek… let it stand nine days in the brass vessel…

Intrigued by the possibility that the recipe had anti-bacterial properties, Harrison set forth on a quest to recreate it as accurately as possible. She looked for heritage vegetable varieties, used historic wine and immersed brass into the mixture so she could use sterile glass bottles. And she sourced “bullocks gall,” or cow bile, using salts that are usually prescribed for people who have had gall bladder removal surgery.

The brew fermented for days, killing off soil bacteria introduced by the vegetables, reeking of garlic and turning downright nasty. “With the nine-day waiting period, the preparation turned into a kind of loathsome, odorous slime,” reported a colleague. But that loathsome slime had a real benefit—when the team tested the brew on scraps of MRSA-infected mouse skin, it killed 90 percent of the bacteria, results comparable to those achieved by the leading antibiotic given to fight the superbug.

Their medieval experiment joins growing calls to turn to age-old recipes for clues on better medicine. Now Harrison and her team will try to see why the concoction fights the bacteria (and whether their discovery can be put to use in new drugs). And we'll need it—another new study shows that antibiotic-resistant bacteria are even spreading through the air, downwind of cattle yards.