It Sounded Plausible: This Kitchen Tip Doesn’t Hold Water

Introduction: Common Advice Revisited

Picture this: You’re rushing to make pasta for dinner, and someone confidently tells you to start with cold water because it’ll boil more quickly than hot water. It sounds logical enough—maybe cold water absorbs heat more efficiently, giving it a head start in the race to 212°F or 100°C. But like many things that sound reasonable, this piece of wisdom is completely wrong.

The Simple Science

The belief that cold water boils more quickly than hot water may have originated as a well-intentioned kitchen tip. Scientists think it might have emerged from experts’ advice encouraging people to cook with cold water, rather than hot water, since hot water can contain more impurities thanks to our household plumbing systems. There’s also a grain of truth buried in the misconception: Cold water does generally gain heat more rapidly than water that’s already hot. However, gaining heat quickly and reaching the boiling point first are different things.

According to scientists, the notion that cold water will reach boiling temperature more quickly than hot water if you keep all other circumstances the same is just false. The reasoning is straightforward: Hot water has already traveled part of the journey to its boiling point. Starting with water at 80°C means you only need to add enough energy to raise it 20 more degrees, while cold water at 20°C requires four times as much energy input to reach the same destination. Think of it like a race where one runner starts halfway to the finish line: Barring any unusual circumstances, the runner with the head start will win.

The Plot Twist: When Hot Water Freezes More Quickly Than Cold

That said, scientists say that the myth that cold water boils more quickly than hot water might also stem from people conflating boiling with an entirely different phenomenon—one where the opposite actually does occur under specific conditions. Here’s where things get interesting. While cold water doesn’t boil more quickly than hot water, hot water can freeze more quickly than cold water. This counterintuitive phenomenon, known as the Mpemba effect, has puzzled scientists for centuries.

The effect got its modern name from Erasto Mpemba, a Tanzanian teenager who observed it in 1963 while making ice cream at school. In his rush to claim the last available ice tray, Mpemba skipped waiting for his boiled milk-and-sugar mixture to cool and put it directly in the refrigerator. 1.5 hours later, his classmates’ mixtures were still in the form of a thick liquid. But Mpemba’s had already frozen into ice cream. When Mpemba asked his physics teacher about this observation, he was told he must be wrong. But the teenager persisted, eventually partnering with physicist Denis Osborne to conduct the first systematic studies of the phenomenon.

The Science Behind the Paradox

Physicists hypothesize that several factors may contribute to the Mpemba effect. Hot water loses mass through evaporation. So, because hot water has less mass than cold water, it’s possible that less energy is needed to freeze the hot water—a phenomenon described as far back as 350 B.C. by Aristotle. Other explanations include the possibility that heating water disrupts hydrogen bonds between molecules, or that external factors like frost layers in freezers create different cooling conditions for hot versus cold containers.

However, scientists explain that proving the Mpemba effect remains challenging. Modern experiments have shown how sensitive the phenomenon is to measurement techniques. Researchers found that thermometer placement could make the difference between observing the effect or not. The difficulty in consistently replicating the Mpemba effect has led to broader questions about systems that are “out of thermodynamic equilibrium,” something scientists know surprisingly little about. Recent research has identified similar phenomena in other materials, from polymers to granular fluids, suggesting that the effect might be more common than previously thought.

The controversy has pushed scientists to develop new theoretical frameworks for understanding how systems relax toward equilibrium—research that could have applications far beyond determining whether your ice cubes freeze more quickly from hot or cold water. So while cold water definitively does not boil more quickly than hot water, the related phenomenon of hot water sometimes freezing more quickly serves as a reminder that our intuitions about the physical world can be misleading.