Ming-dynasty builders boiled sticky rice into a thin soup and mixed it into lime mortar. Nanjing's city wall, built between 1366 and 1393, still stands more than six centuries later.

• ✓Yang, Zhang & Ma, Acc. Chem. Res. 43(6) (2010)
• ✓ACS release via ScienceDaily (2010)
• ✓National Geographic News (2010)

They're not cooking dinner. They're making mortar. Ming-dynasty builders boiled sticky rice into a thin soup and mixed it into lime. It went into walls like this one in Nanjing, six hundred years ago. In 2010, chemists tested this mortar. Inside, they found amylopectin, the starch that makes sticky rice sticky. You'd expect food in a wall to rot. Instead, it changed how the lime hardened. Lime hardens by growing tiny crystals. The starch kept those crystals small and tightly packed, so the mortar set denser and resisted water better. And the recipe is back. Conservators have used it to repair a seven-hundred-year-old bridge in China. Six centuries on, part of the fix for those walls is still a pot of rice soup.