The Asia Economy food and beverage team has been observing the day-by-day decay of flagship products from major burger franchise brands for two weeks.

The signature products of six companies?McDonald’s, Mom’s Touch, Lotteria, Burger King, KFC, and Five Guys?have begun to show clear visual changes. While the degree varies by product, an increasing number of burgers have buns and patties covered in mold, and in several cases, the vegetables have become unrecognizable.

On the 22nd, marking the third week and fifteenth day of the experiment,

The product showing the most severe decay to the naked eye was the Five Guys Bacon Cheeseburger. Even after just one week, by the 14th, white mold had appeared on the bun, beef patty, and tomato, and the cheese had melted?making it the first product to show visible changes. After another eight days, two patches of mold had formed on the top of the bun, and they were much larger than the previous week. Yellow and dark blue spots appeared on the white mold, creating a mushroom-like shape. A wide area of blue mold also developed where the patty and bun met, and the container was filled with moisture, likely produced during the decay process.

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KFC’s Zinger Burger and Mom’s Touch’s Thigh Burger, both using chicken patties, began to show visible mold after two weeks. On the Zinger Burger, a single patch of white mold appeared on the edge of the crispy chicken after one week, and by the fifteenth day, patches of mold had formed in several places, including where the bun, vegetables, and patty met. The overall shape remained largely unchanged from the time of purchase, but the visible vegetables had shrunk in size, and moisture from decay was present. The Thigh Burger also developed two small patches of mold along the side of the bun after one week, and by the fifteenth day, dark blue mold had spread to the patty and grown larger. The inside of the experiment container was so filled with moisture that droplets ran down the walls.

Burger King’s Whopper, which showed little change during the first week, developed its first small patch of white mold on the bottom bun on the eighth day, the 15th. After another week, mold had spread to cover the top of the bun. No other visible changes, such as moisture loss or shrinkage of the patty or vegetables, were observed.

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Previously, in 2020, Burger King released a 45-second global advertisement on its official YouTube channel featuring a Whopper covered in mold after 34 days. With the English tagline "The beauty of no artificial preservatives," the ad emphasized the use of eco-friendly ingredients. In the video, after 34 days, the entire burger?including bun, vegetables, and patty?was covered in dark blue mold. The burger also shrank in size as it lost moisture. Although there may be differences in experimental conditions, we plan to observe whether the Whopper in our experiment will reach a similar level of decay over the next 20 days.

Additionally, McDonald’s Big Mac and Lotteria Bulgogi Burger have shown much slower visual changes compared to other groups over the past fifteen days. Aside from a small patch of white mold about the size of a pinky fingernail on the lower patty and bun of the Big Mac on the eighth day, the overall appearance remained almost identical to the start. For the Bulgogi Burger, a small patch of mold appeared on the edge of the patty on the same day as McDonald’s, and it spread slightly to the lower bun, but no further visible changes were observed.

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During the second week of observation, the temperature at the Asia Economy studio in Chodong, Jung-gu, Seoul averaged 24.4 degrees Celsius, with humidity ranging from 43% to 65%. Asia Economy will continue to monitor which burger resists decay the longest under identical temperature and humidity conditions.