Several people who read our recent article, Keeping the Chicken Water from Freezing, brought up the question:  “which type of water freezes faster, warm (or hot) water, or cold?”

The Dilemma

One reader commented,

Hot/warm water freezes twice as fast as cold! I experimented this past weekend. Stick with cold water.

Another said,

Warm water freezes faster than cold water. This is because when water is warmed up, the oxygen it contains is released, and the less oxygen water contains, the faster it freezes. Cold water contains much more oxygen than warm water and, in order for the cold water to freeze, it must lose some of this oxygen. As it slowly does this, it then starts to freeze. Try it, you’ll see that this is actually true. I was a non believer until I experimented myself……isn’t science cool!

Another reader disagreed,

Warm water does not freeze more quickly than cold water. The rate of loss of the warmer water is higher while it is warmer. The rate is not constant, it slows as the water cools. So it makes sense to start with warm water.

And another reader said,

I don’t get this warm water freezing faster than cold water thing. Warm water will not freeze until it loses it’s heat and becomes cold water. So in the end it is cold water freezing, not warm water. So what can be the difference?

I had read about this phenomenon years ago in a Scientific American magazine and did a little more research on it after reading these comments.  It turns out that another reader gave the most accurate comment which also provided a good place to start the research:

Hot water can freeze first – this phenomenon is know as the “Mpemba effect”.

History

Erasto Mpemba was an secondary school student in Tanzania in 1963.  He was making ice cream in a class at school.  He was in a hurry, and even though he had been told to cool his heated milk/sugar mixture before putting it in the freezer, he didn’t.  He just put the hot liquid mixture into the freezer alongside the pre-cooled mixture of his classmate.  Much to Mpemba’s surprise, his mixture froze into ice-cream before that of his classmate.  He asked his teacher, “Why?” and received the explanation, “you are confused, that cannot happen.”

Mpemba initially believed his teacher’s explanation, but later discussed the matter with a friend who made and sold ice cream, and his friend told him that he alway froze hot mixtures to make ice cream. Other ice cream makers in the area did the same.

Several years later, when Mpemba was in high school, he asked a visiting professor, Denis Osborne why hot (212° F) water would freeze faster than warm (95° F) water.  Osborn did not have an immediate explanation but had a technician perform the experiment in his lab.  The technician confirmed that the hotter water did indeed freeze faster than the cooler water.

Mpemba was not the first to have discovered this effect.  Aristotle, Francis Bacon, and René Descartes also made similar observations.

Conclusions

Does the Mpemba effect always occur? No. It depends on gas and dissolved mineral content in the water, container size, composition, and shape, and the environment around the container of water.  The reasons for the Mpemba effect aren’t well understood, nor or the conditions under which it occurs.  Some factors put forth to explain it are evaporation, dissolved gases and minerals, temperature distributions in the water, supercooling, and changes to the surrounding environment.

Will the Mpemba effect occur in my chicken waterer?  It’s hard to say.  If you enjoy experimenting, you can try it out with two chicken waterers of the same size and design, one filled with cold water and the other with hot.  If you don’t enjoy experimenting, then I recommend using whatever water you have available and not being too concerned with its temperature.  If you find out something interesting from your experiments, leave us a reply.

Further Reading about the Mpemba Effect