Back in 2012, Colin Purrington learned that the snack-food maker Hostess was going out of business. He stocked up on one of the company’s most iconic treats: Twinkies. Purrington, who lives in Pennsylvania, put away a box of the cream-filled, golden cakes in his basement. But then he forgot about them . . . for eight years.

It’s long been rumored that Twinkies can stay fresh for decades. In 2020, Purrington rediscovered his stash of treats and decided to try one. He quickly realized that the rumor was false. The Twinkie tasted horrible! After inspecting the rest of the box, he discovered that some of the treats looked rotten.

Twinkies’ actual shelf life—the length of time a product remains safe to eat—is 45 days. Along with flour, sugar, shortening, and eggs, Twinkies also contain a preservative called sorbic acid. It’s added to prevent spoiling. Eventually, though, bacteria and mold—a type of fungus—will begin to grow on most foods, explains Matt Kasson. He’s a mycologist—a scientist who studies fungi—at West Virginia University.

Kasson and his colleague Brian Lovett tested the eight-year-old baked goods to see what was growing on them. The team found that several had some amount of mold on them. Airborne spores—microscopic cells fungi use to reproduce—likely landed on the Twinkies when they were being manufactured. “In Purrington’s basement, the fungi on the Twinkies had enough time and the proper humidity to grow,” says Kasson.

Purrington’s unappetizing mistake offers a valuable lesson: Make sure to check any food’s expiration date before you take a bite.