Clothes generally dry pretty slowly. It’s a peaceful process. Once in a while, a particularly energetic water molecule finds itself at the water surface with enough energy to escape, and off it drifts. But it doesn’t have to be like that. And violent evaporation can be very useful, especially when you’re cooking. It turns out that frying food, generally classed as a “dry” cooking method, owes an awful lot to water.
My favorite fried food is halloumi cheese, something I’ve always thought of as the vegetarian’s answer to bacon. It all starts with oil heating in a heavy pan, while I chop up rubbery strips of cheese. The oil silently takes in enough heat to raise its temperature to about 350°F, and if I couldn’t feel the heat nearby, I’d never know anything was happening. But as soon as I drop in the first strips of cheese, the peace is smashed by loud crackling and sizzling. As the cheese touches the hot oil, its surface layer is heated up to almost the oil temperature in a fraction of a second. The water molecules at the surface of the cheese suddenly have loads of extra energy, far more than they need to escape the liquid and float off as a gas. And so they burst apart from each other, producing a series of mini gas explosions as the molecules in the liquid are liberated. These bubbles of gas are what I can see at the surface of the cheese, and this is where the noise is coming from. But the bubbles have an important role to play. As long as gaseous water is streaming out from the cheese, the oil can’t get in. It can barely touch the surface, only just enough to pass on heat energy. This is why frying food at too low a temperature makes it greasy and soggy; the bubbles don’t form quickly enough to keep the oil at bay. As the cheese cooks, some heat is transferred into the bulk of the cheese, heating it up. The outer edges give away lots of water, because it’s too hot for liquid water to remain there. This is why the outer surface becomes crispy—it’s dried out. The browning comes from chemical reactions that happen as the proteins and sugars in the cheese get heated up. But the sudden transition from liquid water to gas is at the heart of how frying works. And frying food has to involve sizzling—if you’re doing it right, there’s no way to avoid it.
THE TRANSITION FROM gas to liquid and back again is happening all the time around us. But we don’t see the transition from liquid to solid and back nearly as often. For most metals and plastics, melting happens a long way above everyday temperatures. For smaller molecules like oxygen, methane, and alcohol, melting happens at fantastically low temperatures, the sort of temperatures that require very specialized freezers. Water is an unusual molecule, since it both melts and evaporates at temperatures that occur around us fairly regularly. But when we think of frozen water, we think most often of the North and South Poles of the Earth. They’re cold, white, and forever associated with the great expeditions of the twentieth century that took humans into some of the most inhospitable environments on the planet. Freezing water caused them a lot of problems. But sometimes it also offered unusual solutions.
The transition from gas to liquid is all about molecules getting close enough to each other to touch, while still moving freely enough to flow over each other. The transition from liquid to solid is about the moment those molecules get locked into place. The freezing of water is the most common example of this, but water freezes like almost nothing else. There’s nowhere this weirdness is more visible than the frozen north—the Arctic Ocean.
If you travel to the northernmost part of Norway, stand on the coast, and look still farther north, you see the sea. During the ice-free summer months, the 24-hour daylight nourishes vast mobile forests of tiny ocean plants, a seasonal smorgasbord that attracts fish, whales, and seals. Then, toward the end of the summer, the light starts to disappear. The surface water temperature, which only reached 43°F even at the height of the summer, starts to drop. The water molecules, slipping and sliding over each other, slow down. The water is so salty here that it can get down to 29°F and stay liquid; but one clear dark night, the ice starts to form. Perhaps a flake of ice is blown on to the water, and if the slowest water molecules bump into it, they will stick. But they can’t stick just anywhere. Each new molecule rests at a fixed place relative to the others, and the jumble of bustling molecules is replaced by a crystal, in which well-ordered water molecules are marshaled into a hexagonal lattice. And as the temperature drops further, the ice crystal grows.
The utterly weird thing about water crystals is that the rigorously aligned molecules take up more space now than when they were dashing around in the warm. With almost any other substance, parking molecules on a regular grid would make them sit closer together than when they’re allowed to roam free. But water’s not like that. Our growing crystal is less dense than the water around it, and so it floats. Water expands as it freezes. If it didn’t, the newly frozen ice would sink, and the polar oceans would look very different. But as it is, the temperature drops further, the freezing ice expands, and the ocean grows itself a coat of solid white water.
There are lots of things in the frozen Arctic to get excited about: polar bears and ice and the Northern Lights. But there’s one particular piece of Arctic history that I absolutely love, a story that’s all about the peculiarities of ice freezing, and of working with nature rather than against it. It’s about a bulbous, stout little ship that survived one of the most extraordinary voyages in the history of polar exploration. She’s called the Fram.