Taste: Surprising Stories and Science About Why Food Tastes Good (42 page)

DIRECTIONS

1. There are two tasks in this exercise.

2. The first task is to sample each beverage, then rank the beverages in order of increasing sweetness.

3. The second task is to sample each beverage again, then rank the beverages in order of increasing sourness.

4. The answers appear at the end of the “Sour” chapter,
page 240
.

OBSERVE

1. Keep in mind that sugar and acid balance each other. Some beverages that are very sweet may also be very sour, but the tartness is masked by the sweetness.

2. Discuss your answers with the other tasters.

A
fter Curt Mueller played basketball at the University of Wisconsin in the early 1960s, he headed not to the National Basketball Association but into the lab. As a budding pharmacist, he decided to tackle some of the physiological issues he had faced on the court. During particularly strenuous games his mouth would dry out, resulting in a dreaded condition called cottonmouth. Drinking water was difficult because basketball moves so fast that, if you drank too much, it would slosh around in your stomach. Mueller tinkered with sprays that effectively solved the problem, but when he tested them, athletes had trouble managing the clunky bottles.

In the seventies Mueller launched a chewing gum “that stimulates saliva,” its package promised, for all types of athletes, solving the dry mouth problem in a clever way. Mueller’s gum was so incredibly sour it would make your mouth fill with saliva. He called his concoction Quench.

One of the ways we describe delicious food is by saying that it’s mouthwatering. Sour is the Basic Taste that makes our mouth water most. This happens because a supersour food enters the mouth with more acidity than the permanent resident, saliva, which rushes in to try to manage this huge change in acidity in
the mouth. The more sour the food, the more saliva floods the mouth. Once there’s enough saliva to dilute the sourness, the waterworks stop. That’s why Quench was so brilliant: as you kept chewing it, it kept releasing more acid, which kept the saliva flowing.

Mueller marketed his product as a “sport gum.” Quench did nothing to alleviate thirst, but that was okay, because it wasn’t supposed to rehydrate the body with fluids. It was just supposed to eliminate the dry feeling in the mouth. With a mouthful of spit brought on by chewing the squintingly tart gum, athletes could continue playing, running, or biking a little longer without a break.

Human saliva is made up of compounds that represent all five of the Basic Tastes: glucose, which provides sweet; urea, bitter; sodium chloride, salt; and glutamate, umami. But these Basic Tastes are present at levels that are too low for us to detect consciously. Saliva is very slightly acidic, but when we’re healthy, we don’t think of our mouth as tasting sour, because we are accustomed, or adapted, to the taste of our mouth.

My grandparents used to have an apple tree in their backyard in suburban Baltimore. At a young age I’d climb it to pick apples fresh from the branches, sometimes too early in the season. That didn’t stop me from eating the budding fruit, though. I loved the bracing sourness of the flesh, crisp and only slightly sweet.

If too many days went by between visits to Grandma’s, I might miss the window of time when the apples were perfectly ripe. It was an elusive sliver of autumn between too-tart green apples and overripe red ones that fell off the tree and rotted on the ground. This narrow stretch was when the apples tasted best to the adults, when the fruit had the most perfect balance of puckery acidity and sweet juice. At the precise moment when they are neither too tart nor too sweet, apples also offer—I now know—their peak nutritional value.

Some scientists believe that the biological reason we’re born with a sourness detection system is so that we’ll end up eating more nutritious, riper fruits and vegetables. Apples that are too tart don’t taste good, at least not to babies and adults. The sourness stops us from eating the fruit until it’s ripe—and sweet—enough that we derive the maximum nutrition from it.

Humans can detect sourness from birth. Babies are acutely sensitive to it. If you need proof (and you have an evil streak) you could give an infant a
wedge of lemon and watch him scrunch up his face and push it away.
²⁰
Having a built-in sourness rejection response makes sense, because babies’ developing systems cannot tolerate acidity as well as those of adults. Too much acid in children’s diets can harm their developing teeth and upset their developing digestive systems.

What doesn’t make sense is that kids from about five to nine years of age prefer sour foods at acidity levels that both babies and adults reject. To see this for yourself, just visit a candy store. The candies aimed at children in this age range are not chocolates, caramels, or nuts, but sour candies, some of them promising super, atomic, crybaby, or “toxic” levels of tartness.

Charles Darwin noticed this bizarre phenomenon in 1877 while chronicling the development of his own kids. He wrote:

It looked to me as if the sense of taste, at least with my own children when they were still very young, was different from the adult sense of taste; this shows itself by the fact that they did not refuse rhubarb with some sugar and milk which is for us an abominable disgusting mixture and by the fact that they strongly preferred the most sour and tart fruits, as for instance unripe gooseberries and Holz apples.

Modern-day researchers at Monell conducted tests with mothers and children to find out what levels of sourness each preferred. They scientifically proved what the makers of Warheads, Sour Patch Kids, and Tear Jerkers have known all along. Using gelatin desserts that they spiked with higher and higher levels of acidity, they found that “a striking difference emerged between children and their mothers in their preferences for the extreme sour gelatin.” This difference is what allowed me to enjoy unripe apples and Charles Darwin’s children to prefer “abominable” sour fruits.

What could explain the fact that newborn babies and adults reject sour foods that kids between the ages of five and nine crave? There are many things we don’t know about the sour Basic Taste and the biological reason for it.

Sour is confounding in my work at Mattson as well. In the food development lab, I can increase the acid in a sauce formula to get a very specific response. At low levels of sourness, a slight increase will lead a consumer to say that a tomato sauce tastes fresher than one with less acid. But at some point, an aggressively
sour sauce becomes unpleasant. And if it’s pushed even beyond unpleasantness, a sour taste can burn the tissues in the mouth.

On the one hand sour makes things like tomato sauce taste fresher. On the other, it indicates spoilage. A perfectly balanced white wine will taste brisk and refreshing. A spoiled wine will taste too sour, like vinegar. Fresh milk is creamy and comforting. Spoiled milk tastes sour.

In addition to spoilage, sour is the primary taste of fermentation, which is often used to preserve food. In fact, fermentation is a form of spoilage. After the active cultures develop in sauerkraut and yogurt, for example, the result tastes more sour than before. During a trip to San Francisco in my early twenties, I remarked to my dining companion that the bread tasted tart and made a face as if it had spoiled. “It’s sourdough, you idiot,” my friend reminded me. I simply wasn’t used to my bread tasting sour. Now that I live in San Francisco, if my bread isn’t slightly tangy, I miss the acidity.

We use the words
sour
and
acid
in our daily vernacular. Sour comes from acids and these words describe the sensations.

In the food industry, we measure acid level—or acidity—on a scale from zero to fourteen, with seven as a midpoint. The numbers indicate the concentration of hydrogen ions in the food or beverage, abbreviated as pH.
²¹
Foods that have a pH below 7 are acidic. Anything above 7 is alkaline. Because 7 is the midpoint, a food that has a pH of 7 is called
neutral
, neither acidic nor alkaline. Water has a neutral pH of 7.0. That’s one of the reasons it’s perfect for cleansing the palate. Water helps return the mouth to a more neutral pH. When you’re evaluating food (and anything, for that matter), neutrality is always a good place to start.

The pH of Common Foods, Bodily Fluids, and Household Items
The pH scale is exponential. Each number is 10 times more or less acidic than the next one.

The hardest thing to remember about pH is that a lower pH means a higher level of sourness. A higher pH means a lower level of sourness. For example, a lime has a pH of about 2.0. Milk has a pH between 6.0 and 7.0. The lower pH 2.0 lime is more acidic than the pH 7.0 milk. I know, I know. This makes having a discussion about pH confusing. I wish I could tell you that we have no problem communicating pH level in the food development world, but this “higher is lower” system is counter to what we know about numbers. When we’re talking casually in the lab, we often screw it up and have to correct ourselves.

Just to add more confusion to the pH scale, it’s not a normal, nominal scale. It’s exponential. That means that a pH of 4.0 is ten times more acidic than pH of 5.0. And a pH of 4.0 is ten times less acidic than a pH of 3.0.

Many studies have tried and failed to draw some correlation between an acid, a food, its pH, and how sour it tastes. Using a variety of different acids, you could make up sour water drinks that all measured the same pH—for example, pH 3.0—but when you taste them, they will have different levels of sourness. In other words, if you taste pH 3.0 lemon water (which contains citric acid) versus pH 3.0 vinegar water (which contains acetic acid) versus pH 3.0 lactic acid water (the type of acid in cheese) with your nose pinched shut, you will notice that each has a different level and quality of sourness.