What Einstein Told His Cook (7 page)

Of course, you know that as an incorrigible professor I now feel obliged to tell you
why
salt raises the boiling point of water, small as the effect may be. Give me one paragraph.

In order to boil off, that is, in order to become vapor or steam, water molecules must escape from the ties that bind them to their liquid fellows. Wresting themselves loose with the aid of heat is tough enough because water molecules stick together quite strongly, but if there happen to be any alien particles cluttering up the liquid, it’s even tougher, because the particles of salt (Techspeak: the sodium and chloride ions) or other dissolved substances simply get in the way. The water molecules therefore require some extra oomph, in the form of a higher temperature, in order to make good their escape to airborne freedom. (For more, ask your friendly neighborhood chemist about “activity coefficients.”)

Now back to the kitchen.

Unfortunately, there is even more mumbo jumbo surrounding the addition of salt to cooking water than the fallacy about boiling temperature. The most frequently cited fables, even in the most respected cookbooks, tell us precisely
when
we must add the salt to the water.

One recent pasta cookbook observes that “it is customary to add salt to the boiling water prior to adding the pasta.” It goes on to warn that “adding the salt before the water boils may cause an unpleasant aftertaste.” Thus, the recommended routine is (1) boil, (2) add salt, (3) add pasta.

Meanwhile, another pasta cookbook counsels us to “bring the water to the boil before adding salt or pasta,” but leaves open the momentous question of salt-first or pasta-first.

The fact is that as long as the pasta cooks in salted water, it makes no difference whether or not the water had already been boiling when the salt was added. Salt dissolves quite easily in water, whether hot or merely lukewarm. And even if it didn’t, the roiling of boiling would dissolve it immediately. Once dissolved, the salt has no memory of time or temperature—of precisely when it entered the water or of whether it took the plunge at 212ºF or 100ºF. It cannot, therefore, affect the pasta differently.

One theory I have heard from a chef is that when salt dissolves in water it releases heat, and that if you add the salt when the pot is already boiling the extra heat can make it boil over. Sorry, Chef, but salt doesn’t release heat when it dissolves; it actually absorbs a little bit of heat. What you undoubtedly observed is that when you added the salt, the water suddenly erupted into livelier bubbling. That happened because the salt—or almost any other added solid particles—gives the budding bubbles many new places (Techspeak: nucleation sites) upon which to grow to full size.

Another theory (everybody has one, it seems; is boiling pasta such an Earth-shaking challenge?) is that the salt is added for more than flavor, that it toughens the pasta and keeps it from getting too mushy. I have heard some plausible but quite technical reasons for that, but I won’t trouble you with them. Let’s just add the salt whenever and for whatever reason we wish. Just make sure we add it or the pasta will taste blah.

OH SAY, CAN YOU SEA?

Please tell me about sea salt. Why are so many chefs and recipes using it these days? How is it better than regular salt?

T
he terms
sea salt
and
regular salt
or table salt are often used as if they denote two distinctly different substances with distinctly different properties. But it’s not that simple. Salt is indeed obtained from two different sources: underground mines and seawater. But that fact
alone
doesn’t make them inherently different, any more than water obtained from wells and springs are inherently different because of their sources.

Underground salt deposits were laid down by ancient seas that ultimately dried up at various times in Earth’s history, from a few million to hundreds of millions of years ago. Some of the deposits were later thrust upward by geologic forces and are quite near the surface in the form of “domes.” Other salt deposits lie hundreds of feet below ground, creating a bigger challenge to mining.

Rock salt is chopped out by huge machines within caverns carved into the salt. But rock salt isn’t suitable for food use because the ancient seas trapped mud and debris when they dried up. Instead, food-grade salt is mined by pumping water down a shaft to dissolve salt, pumping the salt water (brine) up to the surface, settling out the impurities, and vacuum-evaporating the clear brine. That creates the familiar, tiny crystals of table salt in your salt shaker.

In sunny coastal regions, salt can be obtained by allowing sunshine and wind to evaporate the water from shallow ponds or “pans” of contemporary seawater. There are many kinds of sea salt, harvested from waters around the world and refined to various degrees.

There are gray and pinkish-gray sea salts from Korea and France, and black sea salt from India, all of which owe their colors to local clays and algae in the evaporation ponds, not to the salt (sodium chloride) that they contain. Black and red sea salts from Hawaii owe their colors to deliberately added powdered black lava and red baked clay. These rare and exotic boutique salts are used by adventurous chefs. They have undeniably unique flavors, of course; they taste like salt mixed with various clays and algae. Each one has its fervent partisans.

In what follows, I am not writing about these rare, expensive ($33 or more per pound) multicolored boutique salts, which are not easily available to the home cook. I am writing about the wide variety of relatively white salts obtained by one means or another from seawater, and which
for that fact alone
are revered because they are believed to be rich in minerals and universally superior in flavor.

MINERALS

If you evaporate all the water from a bucket of ocean (fish previously removed), you will be left with a sticky, gray, bitter-tasting sludge that is about 78 percent sodium chloride: common salt. Ninety-nine percent of the other 22 percent consists of magnesium and calcium compounds, which are mostly responsible for the bitterness. Beyond that, there are at least 75 other elements in very small amounts. That last fact is the basis for the ubiquitous claim that sea salt is “loaded with nutritious minerals.”

But cold, hard chemical analysis tells the tale: The minerals, even in this raw, unprocessed sludge, are present in nutritionally negligible amounts. You’d have to eat two tablespoons of it to get the amount of iron, for example, contained in a single grape. Although people in the coastal regions of some countries do use this raw material as a condiment, the FDA requires that in the U.S. food-grade salt be at least 97.5 percent pure sodium chloride. In practice, it is invariably much purer.

That’s only the beginning of the Great Mineral Deception. The sea salt that winds up in the stores contains only about one-tenth of the mineral matter in raw sea sludge. The reason for that is that in the production of food-grade sea salt, the sun is allowed to evaporate much of the water in the ponds, but by no means all of it—and that’s a critical distinction. As water evaporates, the remaining water becomes more and more concentrated in sodium chloride. When the concentration of salt in the ponds gets to be about nine times what it was in the ocean, it begins to separate out as crystals, because there isn’t enough water left to hold the salt in its dissolved form. The crystals are then raked or scooped out for subsequent washing, drying and packaging. (How do you wash salt without dissolving it away? You wash it with a solution that is already holding as much salt as possible and cannot dissolve any more. In Techspeak, a saturated solution.)

The vital point here is that this “natural” crystallization process is in itself an extremely effective refining step. Sun-induced evaporation and crystallization make the sodium chloride about 10 times purer—freer of other minerals—than it was in the ocean.

Here’s why.

Whenever you have a water solution containing a preponderance of one chemical (in this case, sodium chloride) along with a lot of other chemicals in much lesser amounts (in this case, the other minerals), then as the water evaporates away, the preponderant chemical will crystallize out in a relatively pure form, leaving all the others behind. It’s a purification process that chemists use all the time. Madame Curie used it repeatedly to isolate pure radium from uranium ore.

Salt harvested by the solar evaporation of ocean water, known as solar salt, is therefore about 99 percent pure sodium chloride right off the bat, with no further processing. The other 1 percent consists almost entirely of magnesium and calcium compounds. Those other 75-or-so “precious mineral nutrients” are virtually gone. To get that single grape’s worth of iron, you’d have to eat about a quarter of a pound of solar salt. (Two pounds of salt can be fatal.)

Incidentally, the notion that sea salt arrives naturally iodized is a myth. Just because certain seaweeds are rich in iodine, some people think of the oceans as vast pots of iodine soup. In terms of the chemical elements in seawater, there is 100 times more boron, for example, than there is iodine, and I’ve never heard anybody tout sea salt as a source of boron. Un-iodized commercial sea salts contain less than 2 percent of the amount of iodine in iodized salt.

IS “SEA SALT” SEA SALT?

Actually, the “sea salt” sold in markets might not even have been taken from the sea, because as long as they satisfy the FDA’s purity requirements manufacturers don’t have to specify their sources, and according to industry insiders I have talked with, fibbing does occur. Two batches of salt may have been taken from the same bin at the mine plant and one of them labeled for sale as “sea salt.” Well, of course it is. It just crystallized a few million years earlier. Conversely, on the West Coast of the U. S. the common table salt in the salt shaker is most likely to have come from the sea, rather than from a mine.

The point is that
a salt’s characteristics depend on how the raw material has been processed, rather than on where it came from
. You can’t generalize. Thus, when a recipe specifies simply “sea salt,” it is a meaningless specification. It might as well be specifying “meat.”

ADDITIVES

Sea salt is often specified to avoid the “harsh-flavored additives” in shaker salt. Whether from a mine or a sea, shaker salt does indeed contain anti-caking additives to keep its grains flowing smoothly, because they are tiny cubes and their flat surfaces tend to stick together. But the FDA limits the total amount of all additives to a maximum of 2 percent, and it is invariably much less than that. Morton’s table salt, for example, is more than 99.1 percent pure sodium chloride and contains only 0.2 to 0.7 percent of the anti-caking agent calcium silicate. Because calcium silicate (and all the other anti-caking agents) are insoluble in water, shaker salt makes a slightly cloudy solution.

Other common anti-caking additives are magnesium carbonate, calcium carbonate, calcium phosphates, and sodium aluminum silicates.
These are all completely tasteless and odorless chemicals.

But even if they weren’t, even if expert tasters could detect subtle flavor differences among solid salts due to an additive of less than one percent, the 50,000-fold dilution factor that occurs when the salt is used in a recipe would certainly wipe them out. Just do the math. One percent of a 6-gram teaspoon of salt is 0.06 gram of additive in 3 quarts or more than 3,000 grams of stew: 3,000 ÷0.06 = 50,000.

FLAVOR

There is no denying that some of the finer (read more expensive) sea salts—even below the boutique level—have interesting flavor characteristics. But that depends on how they are used and on what your definition of “flavor” is.

A food’s flavor consists of three components: taste, smell, and texture. With salt, we can pretty much eliminate smell because neither sodium chloride nor the calcium and magnesium sulfates that may be present in some of the less purified sea salts have any odor. (Techspeak: They have exceedingly low vapor pressures.) Nevertheless, our sense of smell is very sensitive, and it is possible that a smell of algae in these less purified salts might be detected. Also, when any kind of salt is inhaled nasally as a fine dust, some people report a slight metallic sensation high in the nose.

That leaves taste and texture: what the taste buds actually detect and how the salt feels in the mouth.

Depending on how they were harvested and processed, the crystals of different brands of sea salt can vary widely in shape, from flakes to pyramids to clusters of irregular, jagged fragments. (Check them out with a magnifying glass.) The sizes of the crystals also can range from fine to coarse, although virtually all of them are coarser than shaker salt.

When sprinkled on a relatively dry food such as a slice of tomato just before serving, the bigger, flakier crystals can deliver bright little explosions of saltiness as they hit the tongue and dissolve or as they are crushed between the teeth. That’s why the savviest chefs value them: for those sensuous little bursts of saltiness. Shaker salt doesn’t do that because its compact little cubes dissolve on the tongue much more slowly. Thus, it is the complex shapes of the crystals, not their nautical origin, that give many sea salts their sensory properties.

The reason that most sea salts have large, irregularly shaped crystals is that that’s what slow evaporation produces, whereas the rapid vacuum-evaporation process used in making shaker salt produces tiny, regularly shaped grains designed to fit through the holes in the shaker. That’s a phenomenon well known to chemists; the more rapidly crystals grow, the smaller they will be.

COOKING

Crystal size and shape are irrelevant when a salt is used in cooking, because the crystals dissolve and disappear completely in the food juices. And once dissolved, all textural differences are gone. The food doesn’t know what shape the crystals were in before they dissolved. That’s another reason why it’s silly to specify sea salt in any recipe that contains moisture, and what recipe doesn’t? Using it to salt the water in which vegetables or pasta are to be cooked makes even less sense.