Some folks like milk or sugar (or both) in their coffee. Others prefer a red-hot chunk of charcoal.

For those looking to avoid a bout of acid reflux, vendors in the Indonesian city of Yogyakarta claim they can neutralize coffee’s acidity with a unique trick. They plunk a piece of red-hot charcoal straight into glasses of sweet, black coffee. The resulting unique brew is known as ‘kopi joss’, or charcoal coffee, with ‘kopi’ being coffee, and ‘joss’ referring to the sizzling sound a burning lump of charcoal makes upon hitting the liquid. Some say the bubbling beverage tastes like regular coffee, while others describe a distinct caramel-y, burnt sugar taste.

In the 1960s, a local coffee-stall owner, known only as “Mr. Man”, differentiated his product by using lit charcoal. According to legend, Man added the charcoal to a cup of hot water, coffee grounds, and sugar, then left the drink to gurgle and hiss. Once he removed the cooled nugget, customers drank up. Initially, Man’s fans were young thrill-seekers, but after (medically unsubstantiated) praise for the charcoal coffee’s health benefits spread, ‘kopi joss’ gained wider appeal.

Sellers still tout the drink’s ability to alleviate gastrointestinal discomfort, but most customers are attracted to the sheer novelty of watching hot charcoal force a tall glass of coffee to boil over.

Yogyakarta is located on Java, the Indonesian island that gives coffee its familiar nickname.

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