Going With the Flow

The average person, stuck on a long plane ride from London to San Francisco, might turn to any number of distractions: a book, a Spotify playlist, a nap. Not Mark Miodownik. A professor of materials and society at University College London, Miodownik uses his 11-hour journey to frame a book-length exploration of the liquids that flow, often unnoticed, through our daily lives.

From the security line, with its ban on liquids over 3.4 ounces, to the jet fuel that propels the aircraft, Miodownik’s tour is at once prosaic and wide-ranging. A discussion of hand soap takes us from ancient Mesopotamia through medieval Europe. The clouds outside the plane window inspire tangents about Chernobyl and Dr. Strangelove. Miodownik’s enthusiasm for his subject turns even the most insipid of liquids—in this case, airplane tea—into an opportunity for wonder and delight. It’s a refreshing way of looking at the world, and one that will revive even the most weary and jetlagged of travelers.

Here’s the thing about tea: because it’s so complex and many variables can affect its flavor profile (the kind of tea, the water, the brew time, and the temperature of the water), it’s quite easy to lose focus. The result: you get a cup of tea that tastes completely unlike the cup you were hoping for. That’s exactly what had happened to the cup of tea I was currently drinking. The flight attendants had done their best, compensating for the lower boiling point of the water on the plane with a longer brew time, and by making the tea in a warmed tall stainless-steel pot, which kept the temperature of the tea high throughout the brewing process. But it had taken them a while to get to me with their trolley, probably fifteen minutes or so since they brewed the tea, and all that time it had just been sitting there, getting cooler and less flavorful by the second. When they finally poured it into my little plastic cup, it had lost most of its fruity and leafy flavors; it had plenty of savory quality, but it was cold, bitter, and acidic, and the plastic cup itself had a distinct sharp flavor. All of this meant that I didn’t get that refreshing, thirst-quenching experience I’d been hoping for—quite the reverse. It was borderline disgusting. I should never have ordered it.

But then I made another mistake. I thought I might be able to rescue the disappointing, boring brown liquid, transform it into something palatable, by using the contents of the little plastic bag the flight attendant had given me. I opened the cylindrical tub of milk and poured it into the cup, using the polystyrene stick to stir the mixture. The color of the tea turned from dark brown to milky ocher—a very pleasing color. I like milky tea. Cows’ milk is sweet and contains a good amount of salt and fat. The fat in milk is shaped in small droplets, each about a thousandth of a millimeter in size, and they give a lot of flavor and a rich mouthfeel to the milk. When milk is poured into tea, those droplets of fat disperse, dominating the color and taste of the drink. They give it a malty, almost caramel flavor, and add a creaminess to the mouthfeel, which opposes tea’s natural astringency. They also absorb a lot of the flavor molecules in the tea, reducing the fruitiness and bitterness, but making it creamier.

When to add the milk to your cup is a BIG bone of contention in Britain. There are those who advise adding it before the tea, on the grounds that the droplets of milk will be gently heated as more and more hot tea is added. This keeps the milk proteins from reaching temperatures that would transform their molecular structure, denaturing them and giving the milk a curdled, off flavor. Some people also argue that pouring the milk in first protects ceramic teacups from the thermal shock of the hot tea, thus keeping them from cracking; even if this was historically true, it’s no longer an issue, as modern ceramics are much stronger. But for others, the very notion of pouring the milk in first is anathema. In their perfect cup of tea, you put the tea in first, and then the milk. George Orwell was in this camp, arguing that this allows you to add exactly the right amount of milk for your preferred level of creaminess.

You might doubt whether adding the milk before or after makes any difference to the taste—it being such a subtle distinction. But in an experiment now known as “the lady tasting tea,” the statistician Ronald Fisher investigated this question rigorously, inventing new statistical methods to do so. In his randomized tasting experiments, he found that yes, people can taste the difference between tea with milk poured in before or after the tea.

The methods that Fisher devised revolutionized the mathematical discipline of statistics. It unfortunately did not revolutionize tea making in Britain, so even now if you order a cup of tea in a café, very rarely will anyone acknowledge that the sequence of milk and tea makes any difference. This drives me absolutely mad. Often, in a train station for instance, a server just plonks a teabag into a cup of hot water, immediately sloshes in some milk, then hands the cup to you, as if to say, “I’ve added all the ingredients, so it must be tea.” “But you haven’t asked me if I want the milk before or after,” I sometimes say, when my inner rage boils over. Not that I actually want milk added before. I’m with George Orwell on this; I want the milk added after.

Excerpted from Liquid Rules by Mark Miodownik Copyright © 2019 by Mark Miodownik. Reprinted by permission of Houghton Mifflin Harcourt Publishing Company. All rights reserved.