The Surprisingly Complicated Physics of Condensed Milk

Condensed milk made its inventors a fortune — because it represented a scientific breakthrough. Most food science progress is made through chemistry or biology — but this one owes a lot to physics. Learn why in space, no one can hear you make condensed milk.

Condensed milk is now generally only of interest, today, when you're camping or stocking your shelves for the inevitable nuclear winter to come. We have refrigeration, grocery stores, the FDA, and a good infrastructure, all of which make milk available at ever corner. But back when cities were expanding, farms were growing more distant, and rail and sea travel could take days, buying a carton of milk was like playing bacterial Russian roulette.


Along came Gail Borden. A dairy farmer who'd turned to inventing, he had lost his shirt trying to market "soup bread," a mix of flour and dried meat that not even soldiers would eat.

In 1856, he came up with "condensed milk." Canning had just swept the nation, and allowed people to eat out-of-season fruit and vegetables. Canned vegetables were also useful for long boat voyages. Borden took such a voyage and noticed that, when the waves got bad enough for the cows on board to be sick and stop giving milk, the infants on board starved. He managed to condense and sweeten milk, and so preserve it indefinitely. His new milk product got off to a rocky start, but when the Civil War started, and armies needed to be outfitted with provisions, Borden became rich – and resented. (While some appreciated his inventions, some did not care for the idea of anyone making a fortune from a war.)

But how did he come up with this invention in the first place? People had already tried cooking and condensing milk. What they'd come up with is puddings, scalded milk ice cream, and caramel. Milk is a good bit water. That water can be dispensed with (and along with it, some of the threat that the milk will go off due to bacteria). But boiling the water off requires temperatures that permanently change the proteins and fats in milk. How is this conundrum to be resolved? With physics, of course!


Water only stays in liquid form on Earth because it's under pressure. Atmospheric pressure keeps its boiling point low. As you gain altitude (and lose pressure) water is more disposed to boil, and so the temperature required to boil it goes down. If you went high enough into the atmosphere, you could dabble your hands in boiling water, because the temperature at which water would boil is so low that it wouldn't hurt you. (The low pressure itself might hurt you, though.) In a vacuum, water boils away all on its own, turning to vapor. Using an air-tight container to created near-vacuum conditions, Borden was able to boil away the water in milk at such low temperatures that he didn't need to scald the milk.

[Via Mad Science, Made How.]


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