After winning a gold medal at the Japan Fried Chicken Grand Prix, the owner of Wakatori gave an interview in which he revealed that the secret to the restaurant’s success was a secret ingredient that had been reused since the eatery opened, 66 years ago. Apparently, since the shop’s founding in 1960, the frying oil has never been completely discarded.

Yoshihiro Tsuchiya, the third-generation owner of Wakatori, openly admitted that the oil reused for decades is the key to his family’s delicious fried chicken. The ‘aged oil’ allegedly gives the Wakatori fried chicken a “complex aroma” and “unique flavor” that cannot be replicated with new oil, giving the eatery a leg up over the competition.

As you can probably imagine, Tsuchiya’s revelations caused quite the uproar on social media, with many claiming that Wakatori was putting people’s lives at risk by frying chicken in 66-year-old oil. However, the Japanese award-winning eatery clarified that the quality of the oil is maintained through daily cleaning, filtering, and adding new oil.

Every night, the restaurant staff carefully filters out meat scraps and impurities from the oil, retaining only a small amount of old oil as a flavor base, and adding it to a new batch of frying oil. So they are not using the exact same oil from 66 years ago, but, technically, molecules from that original batch may still be present in Wakatori’s oil blend.

By preserving some of the old frying oil and topping it off with fresh oil, Wakatori is essentially using the same technique some restaurants use for their soup broths. In fact, the oldest oden soup in existence is believed to be used at Otafuku, a famous restaurant in Tokyo, Japan. It has been topping off the same broth for over 70 years. Similarly, a restaurant in Bangkok’s Ekkamai neighborhood has been serving the same batch of soup for over 50 years.

In the case of Wakatori, food experts warn that oil is not the same as broth, because frying it repeatedly produces harmful and carcinogenic substances such as trans fatty acids and acrylamide. Even by diluting it daily with fresh oil, the long-term accumulation of these harmful substances cannot be completely prevented.