Cooking for Geeks: Real Science, Great Hacks, and Good Food (20 page)

Sour tastes are caused by acids in foods. The sensation of sourness is detected by part of the taste bud (ion channels) interacting with the hydrogen ions in the acids. Quite literally, your sour taste buds are a primitive chemical pH tester. In cooking, lemon juice and vinegar are commonly used to make dishes more sour, sometimes for effect but more often to bring balance. When cooking, taste the food and think about the balance of both saltiness and sourness, adding an ingredient such as vinegar to “brighten up” the flavors.

From an evolutionary perspective, we appear to have evolved to taste sourness as one method of determining spoilage, because a number of acids are produced by bacteria during the breakdown of food. This isn’t to say that sourness in food is always due to bacterial breakdown or that the fermentation caused by bacterial breakdown necessarily results in bad food. Lemon juice is sour due to citric acid, and yogurt (pH of 3.8–4.2) acquires a sour taste because of the lactic acid created by the bacteria breaking down the lactose in the milk (pH of 6.0–6.8).

To get a better understanding of how bacteria make the taste of a food more sour, try making your own yogurt using the recipe in
Yogurt
, tasting the liquid before and after fermentation.

We’re hardwired to like sweet foods — no surprise here. Sweet tastes signal quickly digestible calories (and thus fast energy), which would have been more important in the days when picking up the groceries also involved picking up a spear.

Our desire for sweetness changes over our lifespan. Researchers have found that our preference for sweetness decreases as we mature. A child’s preference for sweet things is biologically related to the physical process of bone growth. (Quick, kids, run and tell your parents
that your sweet tooth is because of
biology
!) And the infamous sweet tooth isn’t unique to American kids either; this finding holds up in other cultures.

Sugar is good at simultaneously promoting other flavors while masking sour and bitter tastes. Take ginger, which has a strong, pungent, and slightly sour taste. With a bit of sugar, it becomes enjoyable on its own; sugared and dipped in chocolate, it becomes irresistible. Try making a simple ginger-flavored syrup (recipe at right).

Umami (a Japanese word that roughly translates to “savory”) generates a meaty, broth-like, lip-smacking sensation typically triggered by some amino acids and nucleotides (glutamate is the poster child; inosinate, guanylate, and aspartate are also not uncommon). Glutamate is naturally present in a number of foods, especially mushrooms. To an average American palate, umami is more subtle than the four primary tastes. It tends to amplify our other senses of taste. For example, in dishes with salt, umami “brings out” the salty taste, meaning that you can cut the amount of salt in a dish by adding umami-tasting ingredients.

If you’re unable to imagine the taste of umami, make a simple broth by rehydrating a tablespoon of dried shiitake mushrooms in 1 cup (240g) of boiling water. Let the mushrooms steep for at least 15 minutes, and then remove them and save them for something else (
mmm
, stir-fry). Taste the liquid; it will have a high glutamate content dissolved out from the mushrooms. (If this is too much work for you, I suppose you could just snag a container of MSG from your local Asian grocery store and dissolve a small amount in a glass of water.)

Why we’ve evolved to have taste sensors for umami isn’t fully clear. Sweetness and saltiness are both associated with positive attributes of food (quick energy in the case of sweets and an element essential for regulating blood pressure in the case of saltiness), while sourness and bitterness indicate potential danger. Perhaps umami is a more subtle indicator of protein content, as a way of ensuring we ingest enough amino acids to maintain muscle function. Regardless, umami is worth understanding for the hedonistic value alone. MSG (monosodium glutamate) is to umami what sugar is to sweetness: as a chemical, it’s relatively odorless (still full of taste!), but it triggers the umami receptors on the tongue. MSG has gotten a bit of a bad rap in the United States, but so have salt and sugar at various times.

There are plenty of natural sources of glutamate. Many traditional Japanese dishes call for
dashi
, a stock made from ingredients high in natural glutamate such as kombu seaweed (2.2% glutamate by weight). Making dashi is super easy: in a pot, place 3 cups (700g) cold water and a 6” / 15 cm strip of kombu (dried kelp), and let rest for 10 minutes. Bring to a boil slowly on low heat. Remove the kombu just before the water begins to boil and add 10g of bonito flakes (flakes of dried and smoked bonito fish). Bring to a boil, remove from heat, and strain out the bonito flakes. This liquid is dashi. To make miso soup, add miso paste, diced tofu, and (optionally) sliced green onions, nori, or
wakame
(an edible seaweed).

Glutamate occurs naturally in many other foods — for example, beef (0.1%) and cabbage (0.1%). And if you’re like most geeks and pizza makes your mouth water, it might be because of the glutamate in the ingredients: Parmesan cheese (1.2%), tomatoes (0.14%), and mushrooms (0.07%).

Glutamate content of common ingredients.

In addition to the primary sensations of taste, our taste buds also respond to oral irritation brought about by hot peppers (typically from the chemical capsaicin), cooling sensations (typically menthol from plants like peppermint), and carbonation. The reaction to hot peppers is governed by a neurotransmitter called
substance P
(P is for
pain
; go figure). In one of nature’s more subtle moves, substance P can be depleted slowly and takes time — many days, possibly weeks — to replenish, meaning that if you eat hot foods often, you literally build up a tolerance for hotter and hotter foods as your ability to detect their presence goes down. Because of this, asking someone else if a dish is spicy won’t always tell you if it’s safe to jump in. Carbonation in soft drinks also irritates the taste buds, but in a different way that stimulates
the somatosensory system. Carbonation also interacts with an enzyme (carbonic anhydrase 4) to trigger our sour taste receptors, but for now it’s unclear as to why it doesn’t actually taste sour to us.

Our mouths also capture data for a few chemical families present in some foods, along with noticing texture and “mouthfeel.” Some of the sensations picked up by our mouths include pungency, astringency, and cooling. Pungency is commonly described as being like some strong, stinky French cheeses: a sharp, caustic quality. Astringency results when certain compounds literally bind to taste receptors and causes a drying, puckering reaction. Astringent foods include persimmon, some teas, and lower-quality pomegranate juices (the bark and pulp are astringent). Cooling is the easiest to understand: the chemical menthol, which occurs naturally in mint oils from plants such as peppermint, triggers the same nerve pathways as cold. Menthol is commonly used in chewing gum and mint candies.

Different cultures give different weights to some of the sensations listed here. Ayurvedic practices on the Indian subcontinent include food recommendations as part of their prescriptions, defining six types of taste: sweet, sour, salty, warm (like “hot” but not the same kind of kick), bitter, and astringent. No umami, but two additional variables: warm and astringent. Thai cooking also defines hot as a primary taste. For most European cuisines, these additional variables are of lesser importance, possibly due to genetic differences in taste receptors related to supertasting between Europeans and Asians.