What Einstein Told His Cook (28 page)

The moral of the story is always to check the “drink by” dates on your plastic pop bottles. A visit to my supermarket showed that Coke and Pepsi products are dated, but many other brands aren’t, except in the form of unintelligible codes. Store them all in a cool place—heat deteriorates the flavor—and chill thoroughly before opening.

And, yes, if your sister-in-law’s purveyors aren’t careful about how they handle the soda during distribution, or if it has been on their shelves, or hers, for years, it’s quite possible that when opened it will be as flat as her budget.

HOW TO FIX A FLAT

What’s the best way to keep soda pop from going flat?

I
f you can’t finish the whole bottle and you want to keep the leftovers gassy and sassy until the next pizza, just stopper it tightly and keep it cold. You knew that. But why?

The objective is to keep all of the remaining carbon dioxide in the bottle, because it’s the carbon dioxide, bursting its tiny bubbles on our tongues, that gives us that nice tingly sensation. Also, carbon dioxide dissolved in water makes a sour acid: carbonic acid, which provides tartness. A tight stopper, obviously, keeps the gas from escaping. But the necessity of keeping the soda cold may not be so obvious.

For reasons that are better covered in Chemistry 101 than in Food 101, the colder a liquid is, the more carbon dioxide (or any other gas) it can absorb and hold. Your soda, for example, can hold about twice as much carbon dioxide at refrigerator temperature as at room temperature. That’s why there’s a big blast of escaping gas when you open a can of warm soda or beer: There’s a lot more gas in there than can stay dissolved in the warm liquid.

Now how about those pump-up fizz retainers that are sold in supermarkets and discount stores? You know, the ones that work like a miniature bicycle pump. You screw the thing onto your partially depleted two-liter soda bottle, pump the piston a few times, and put it away in the fridge. The next time you open the bottle, you’re treated to the biggest, most satisfying whoosh! you ever heard, and you’re supposed to think, Hallelujah! My soda is born again!

But guess what? There isn’t one bit more carbon dioxide in there than if you had simply screwed the cap on tight. What you’ve pumped into the bottle is air, not carbon dioxide, and air molecules are totally irrelevant to the behavior of carbon dioxide molecules. (Techspeak: It is solely the partial pressure of CO
₂
that determines its solubility.)

That pump-up gizmo is nothing but a fancy stopper. Save your money.

TO YOUR HEALTH!

SHOWER POWER

When I open a bottle of Champagne, it often foams up all over the place, and I hate to waste that expensive stuff. What makes it behave that way?

T
he bottle had undoubtedly been treated roughly some time earlier, without having been given enough time to recover. It must rest quietly on ice or in the refrigerator for at least an hour before being gently removed and opened.

In contemporary American society, Champagne is not meant to be drunk anyway. It is meant to be sprayed at Super Bowl winners in locker rooms.

The proper technique for these ebullient shenanigans, which I record here purely for its scientific and educational value (DO NOT TRY THIS AT HOME!), is first to pour out a little of the liquid to get more shaking space, then place a thumb over the bottle’s opening, shake the bottle vigorously, and quickly slide the thumb slightly backward—not sideways!—in order to aim a concentrated stream of frothing liquid precisely in the forward direction.

The scientific and educational point I want to make is this: The reason the liquid squirts out is not—repeat, not—because of any increased gas pressure within the bottle. You could fool any number of chemists and physicists on this point, but it’s true. The gas pressure does go up temporarily inside a shaken, sealed bottle, but that’s not what propels the liquid, because as soon as you pop the bottle open or slide back your thumb the pressure drops down to that of the air in the room. And anyway, how could gas pressure in the space
above
a liquid shoot the liquid out of the bottle? The powder charge in a bullet has to be
behind
the slug, doesn’t it?

Then why does the liquid shoot out with so much force when you release it immediately after shaking? The answer lies in the extremely rapid release of carbon dioxide gas from the liquid; that’s what provides the shower power. It’s like an air gun that gets its power from the sudden release of trapped air. There is something about shaking the bottle that makes the gas want to escape almost instantly from the liquid. And in the mad rush to escape it carries a lot of liquid along with it.

Here’s why.

Carbon dioxide dissolves very easily in water, but once it’s there it is extremely reluctant to leave. For example, you can leave an open bottle of soda, beer, or Champagne on the table for several hours before it will go totally flat. One reason for this is that gas bubbles can’t just form spontaneously. The gas molecules need something to grab onto, some kind of an attractive gathering place where they can congregate in one spot until there are enough to form a bubble. The gathering spots, called nucleation sites, might be microscopic specks of dust in the liquid or tiny imperfections in the container’s wall. If there are very few such nucleation sites available, the gas won’t form bubbles and will stay dissolved in the liquid. Beverage bottlers use highly filtered water for that reason.

But if many nucleation sites happen to be available, gas molecules will quickly gather around them and form baby bubbles. As more and more gas molecules gather, the bubbles grow, eventually becoming big enough to rise through the liquid and escape at the surface.

Shaking the bottle puts millions of tiny bubbles into the liquid from the gas space—the “head space”—above the liquid. These baby bubbles are extremely effective, ready-made nucleation sites upon which zillions of other gas molecules can quickly gather to form bigger and bigger bubbles. And the bigger the bubbles become, the more surface they offer for their fellow gas molecules to gather upon and the faster they grow. Thus, shaking the container immensely speeds up the release of gas, which occurs with such explosive force that a lot of liquid is swept along with it. Result: a very effective weapon for drench warfare.

Fluid fusillades aside, there are a couple of peacetime implications of these principles.

First, you don’t have to be afraid that jostling or shaking an unopened bottle or can of carbonated beverage will make it explode. Shaking it will indeed sweep out some gas from the liquid into the head space, but there just isn’t enough head space in the bottle to hold much pressure. Besides, not long after a can or bottle has been shaken, all the baby-bubble nucleation sites will have risen back into the head space, where they can no longer do their dirty deed of, if you’ll pardon the expression, releasing gas. Just don’t open a container right after it has been shaken, while the nucleation bubbles are still distributed throughout the liquid. Let it rest first, to return to what chemists call “a state of equilibrium.”

The trick with Champagne and other sparkling beverages is to let them rest quietly for a couple of hours before opening them. What is so effective about fizzical combat is that you release the bottles’ contents immediately after shaking, while the bubbles are still down inside the liquid making their bubble trouble. But remember: Even though the Champagne is well rested, the Geneva Convention strictly forbids aiming a Champagne cork at anyone, civilian or combatant; it can do serious damage.

One last point: Because heat expels some of the gas from the liquid into the head space, a warm beverage will spritz more upon opening than a cold one will. That’s the other trick with Champagne; it must be cold. In fact, heat can cause so much gas pressure in the head space of a beverage container that an occasional can or bottle has burst in the trunk of a car parked in the hot sun.

SAVOIR FAIRE

What’s the best way to open a bottle of Champagne without looking like a bumbling idiot or hitting the ceiling with the cork?

T
he most important thing in opening a bottle of Champagne is to accomplish the task with such aplomb that it will appear to your guests as if you do it every day. This is very difficult to pull off while wincing at the expectation of imminent disaster. So conquer your fears by practicing a couple of times alone with some cheap sparkling wine as follows.

First, remove the foil wrap covering the wire muzzle and the cork. To help you do that neatly without tearing all the foil away from the neck of the bottle, there is often a small tab to pull. (In my experience, either I can’t find it or it tears off when I pull it.)

With one hand, grasp the bottle firmly around its neck while pressing your thumb down on the top of the cork as insurance against the embarrassment of a premature evacuation. With your other hand, untwist the wire loop at the base of the muzzle and remove the wire. Now move your bottle-holding hand down to the bottle’s widest part and tilt it away from you at a 45º angle. (More about that later.) With your free hand, grip the cork firmly and twist the bottle—not the cork—until the cork begins to loosen, and then continue more slowly until the cork eases out. If you are faced with a recalcitrant cork that refuses to move, rock the cork with a forward-backward motion to loosen the stickiness between the glass and the cork.

Now, why did I say that you should twist the bottle, not the cork? Both Newton and Einstein agree that it shouldn’t matter at all which one you twist, because the motion is strictly relative. You could slice a loaf of bread by rubbing the loaf against the knife, couldn’t you? But think about it: In twisting out a cork, you must reposition your fingers several times, temporarily relinquishing your grip on it. During one of those times, it could pop out uncontrollably, depositing wine on the floor and egg on your face.

About tilting the bottle: You don’t want it to be vertical, of course, because you’d be in danger of shooting yourself in the face if the cork popped out. On the other hand, if the bottle is too close to horizontal the neck gets filled with liquid and the “head-space” gas floats up to form a bubble in the bottle’s shoulder. Then, when you release the pressure by removing the cork, the bubble expands suddenly, expelling the liquid in the neck. A 45º tilt will usually ensure that the head-space gas stays up in the neck, where it belongs.

A REAL CORKER OF A PROBLEM

Some of the wines I buy have “corks” made of plastic. Is there a world cork shortage, or are there technical reasons for this?

I
asked the same question on a trip to Portugal and western Spain, where more than half of the world’s cork is grown, but I was unable to get a satisfactory answer. It was like asking a silkworm about polyester.

Back home, I learned why many wineries are switching to plastic stoppers. Yes, they’re more economical than top-grade natural corks, but it’s as much about technology as economics.

We all learned in school that cork grows on trees called cork oaks. After picturing thousands of tree-ripened corks hanging from the branches, we were disappointed to learn that corks are actually cut from the bark of the tree.

Cork oaks are the very model of a renewable resource, because once the trees have reached maturity, which takes twenty-five years, the bark grows back time and again after being stripped. This is done by scoring circles around the trunk and large branches, slitting the bark lengthwise, and peeling it off in sheets, which are then boiled in water, stacked, and flattened. In the miles upon miles of cork oak groves that I saw in Portugal, each tree was marked in white paint with a big number, indicating the year in which its bark had last been stripped. It would be stripped again nine years from that date.