It’s a horrible scene. You’re hosting a group of friends, shaking (or stirring) up cocktails for your guests, and as you go to prepare another round, you find yourself coming up short as you reach for your ice tray. There’s none left, and you have several cocktails to make. Going with common sense, you quickly flip your tap to the coldest setting, hoping that in doing so, you’ll speed up the process and have your ice ready a bit faster. But is this really the best way to ensure your water freezes fast? Scientists aren’t so sure.
In fact, there are some who in fact argue the exact opposite: Boiling water will freeze faster than cold water. Known as the Mpemba effect, this phenomenon was reportedly observed by Erasto Bartholomeo Mpemba when he was a child. In a paper published in the journal Physics Education in 1969, Mpemba recalls making ice cream with his classmates in secondary school only six years prior. With limited space in the icebox, Mpemba says he was in a rush to grab the last available ice tray and, without letting it cool, poured his boiling milk and sugar combination into the tray before placing it in the freezer.
“I decided to risk ruin to the refrigerator on that day by putting hot milk into it,” Mpemba explains. However, just 30 minutes later when he went to check on his concoction, he found fully frozen ice cream, while his other classmates, who had waited for their mixtures to cool to room temperature before freezing, were met with “a thick liquid, not yet frozen.” When Mpemba questioned how this happened, his physics teacher explained that he was just confused; that it was impossible for that to have happened.
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Unwilling to relent, when physicist Denis Osborne came to visit Mpemba’s school in Tanzania, the teenager questioned the professional as to why, when you take two beakers with equal volumes of water, “one at 35 degrees Celsius and the other at 100 degrees Celsius, and put them into a refrigerator, the one that started at 100 degrees freezes first.” Stumped yet interested, Osborne promised to test the theory out for himself when he returned home. The two spent the next years experimenting on the phenomenon and in 1969 co-wrote a scientific paper on the phenomenon entitled “Cool?”
So, how and why, exactly, does this happen? There have been a variety of theoretical explanations offered to explain the rationale behind the Mpemba effect. One explanation is that boiling temperatures force water to lose a network of hydrogen bonds, throwing the liquid further out of equilibrium, and in turn lowering the amount of energy necessary to freeze it. Another explanation suggests that cold water contains dissolved gasses that lower the freezing point of water but burn off when the water boils.
While the effect has been observed and theoretical explanations have been developed, Mpemba himself stated in 1969 that “theory differs from practical,” and many other scientists have expressed their skepticism. As it turns out, mimicking the conditions necessary to observe the Mpemba effect is notoriously difficult.
In an experiment testing the Mpemba effect in 2016, physicist Henry Burridge and mathematician Paul Linden observed a variety of results depending on a host of variables. For one, their conclusions depended on what the definition was for “freezing,” as they observed that hot water may form ice crystals faster but takes longer than cold water to freeze thoroughly. The study concluded that hot and cold waters’ freezing times were so similar that any data gathered was insignificant in proving the veracity of the Mpemba effect.
So, while boiling water for ice may speed up freezing time in some carefully controlled instances, it may not be the best solution for last-minute cocktails. Instead, you could perhaps try scaffa, ice-free cocktails that have been served since as early as the 19th century. Undiluted and flavor-forward, scaffas could be the perfect solution for ice emergencies when you’re looking to keep the booze flowing at your next gathering.