There’s a bunch of different iterations of people photographing how their McDonald’s burger left out for a long time doesn’t get moldy, and they’ve gotten lots of internet attention. But they all forgot to do something very simple: make a homemade burger and document it alongside.

The food detectives over at A Hamburger Today, however, did not forget. They took a McDonald’s burger and made one from natural ground beef at home, left it out, and observed the results. Turns out that a homemade burger doesn’t rot either.

It’s not the salt that does it, it’s all about surface area and moisture loss. A regular hamburger, McDonald’s or otherwise, is just too flat and well-cooked to retain enough moisture to let mold grow.

Read the whole in-depth experiment here.

The Burger Lab: Revisiting the Myth of The 12-Year Old McDonald’s Burger That Just Won’t Rot (Testing Results!) [A Hamburger Today]

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What Really Happens To A McDonald’s Burger When You Leave It Out
Why McDonald’s Never Rots
This 1-Year-Old Happy Meal Has Aged Surprisingly Well

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