At a base level, the role of taste is to satisfy appetite and to protect us from substances that are dangerous to us. As Brillat-Savarin said, “Taste seems to have two chief uses: First, it invites us by pleasure to repair the losses which result from the use of life, and second, it assists us to select from among the substances offered by nature, those which are alimentary.”

To illustrate, we like the taste of sugar because we physically require carbohydrates. At certain times we crave salt because we have a need for sodium chloride in our diet. Bitter and sour tastes often cause negative reactions because most poisons are bitter and spoiled food tastes sour. Our bodies require protein, and amino acids are the building blocks of protein; thus umami—a sort of “savoriness” often found in fermented and aged foods, and which is produced by free glutamates—drives our appetite when we have a need for more protein.

Whenever you drink or eat something, one or a combination of those five tastes—sweet, salty, sour, bitter, and acidic—provides you with vital information about what has just entered your mouth. If it’s sweet, maybe it has the nutrients your body needs to keep running for another few hours. If it’s salty, perhaps you can replace some of the vital minerals you’ve depleted. If it has umami, maybe it can rebuild muscle tissue broken down from your workout. If it’s sour, there’s a chance that it has gone bad and will give you a stomachache. And if it’s bitter, watch out—it could be poison and that might be your last warning.

Now, in reality you’re not thinking about any of this when you are cupping coffees or sipping a latte. You’re not even thinking about it when you’re grabbing a quick burrito for lunch. Most of the time you just want something that tastes good.

But deciding what tastes “good” is actually quite complex and often poorly understood. The flavor of coffee (or any food or drink) doesn’t usually depend on data from a single sense. Instead, it is the result of a synthesis of various senses. With coffee, this always includes smell and can often also include touch, sight and even hearing. Determining the best ways to excite those senses in order to make people experience something as “good” is what all of us—along with thousands of other restaurant, food and beverage professionals the world over—are in the business of doing.

Open your mouth and you’ll see a big pink chunk of flesh hanging around in there. That, of course, is your tongue, the muscle that we all associate most closely with taste. You’d probably call the little knobs dotting the surface of your tongue taste buds. But these “taste buds” are actually known as papillae and are bunches of 30 to 100 elongated cells. These elongated cells are the true taste buds. Taste papillae can be seen on the tongue as little red bumps, particularly at the front of the tongue. These ones are actually called fungiform papillae, because they look like little mushrooms (fungi). There are three other kinds of papillae: foliate, circumvallate and filiform.

People tend to think that taste buds exist only on your tongue. In fact, taste buds are located throughout the mouth. They exist in the pharynx, where your mouth, throat and nasal passages meet; in the laryngeal epiglottis, where the root of the tongue attaches to the larynx; and at the entrance of the throat itself. Taste buds on the tongue are, in fact, the most numerous (the total number of all taste buds averages about 4600 per tongue) and the most studied of all taste end organs. But there are, on average, an additional 2500 taste buds in those other locations.

This dispersion of taste buds is one of the primary reasons behind the technique of “slurping” coffee when cupping it. By spraying the coffee in a partially atomized mist throughout your mouth and pharynx, you get the maximum taste experience of that coffee because it comes into contact with as many taste buds as is possible. Conversely, if you simply taste with your tongue, more than one-third of the potential of your palate is going unused.

You might remember from high school biology class a map of the tongue that grouped the buds detecting sweetness on the tip of the tongue. Those, in turn, were flanked by the salt-detecting buds, and the sour ones ran farther back along the sides. The bitter buds then ran across the back of the tongue.

While this well-known map of the tongue’s physiology is very tidy and clean, it is also not entirely accurate. As noted above, there are taste buds throughout your mouth, even on the upper palate. And perhaps even more importantly, the truth is that any bud anywhere is capable of detecting all of the basic tastes—it’s just that some buds are more sensitive to a particular taste than to the others. Fungiform papillae are concentrated on the tip and forward-most sides of the tongue. In 1974, researchers discovered that the bud could respond to either salt alone or salt and sucrose combined, and that the responses to salt and sucrose occurred in different cells within the taste bud (Collings, V. B. 1974. Human taste response as a function of location of stimulation on the tongue and soft palate. Percep. Psychophys. 16:169-74). So, we now know that fungiform papillae are salt-sensitive, but this does not mean they are insensitive to other tastes. Bitter receptors, however, do not appear to be uniformly distributed over the tongue. Rather, they are more concentrated in the foliate and circumvallate papillae situated at the sides and the back of the tongue.

So from this revelatory information, we can conclude that the classic “taste map,” while holding some truth, is ultimately an oversimplification of the palate. It’s safe to say, however, that sensitivity to all tastes is distributed across the whole tongue and indeed continues directly to other regions of the mouth where there are taste buds. But it is also true that some areas of the tongue and mouth are more responsive to certain tastes than others.

This is yet another reason for the whole slurping ritual when cupping coffee. By getting as many taste buds as possible involved in the evaluation of the coffee, you are getting a more complete picture of the whole flavor profile of the coffee.

And that brings us to our next question: how does it all really work?

The Science of Slurping

When coffee (or anything else) enters your mouth, its chemical components are dissolved into their base molecules by your saliva. The molecules then enter a taste bud through a pore in its center. There, the molecules selectively bind to receptor cells based on their chemical structure. If the molecule binds to a cell, it causes that cell to issue a series of chemical and electrical signals to your brain that result in your identifying the substance’s taste.

For example, sweet (and some bitter) taste components activate gustducin, a protein that functions as a chemical messenger. The activation of gustducin causes electrochemical “communication” among the receptor cells, which then transmit a chemical message to the basal cells at the bottom of the bud. The basal cells can also “talk” back to the receptor cells and among themselves. The resulting data from this chatter is finally relayed to the gustatory cortex within the brain. The whole process only takes a fraction of a second, so that, seemingly, the moment something with loads of sugars enters your mouth, your brain receives a message of, “Damn, that’s sweet!”

Salty and sour molecules permeate the taste cells directly through special channels in the cell membranes. For example, the channels allow electrically charged sodium ions in, and potassium ions out. This alters the charge of the cell and, as the interior of the cell grows more positively charged, the resulting small electric current triggers more intercellular messages until, once again, word is passed onto the brain that something salty, like a tortilla chip, is heading towards your stomach.

In a lot of cases, you have an idea of how something will taste before it enters your mouth. Think of that leftover General Tso’s chicken that’s been sitting at the back of your refrigerator for a month. If you open the take-out box, odds are you’re going to know instantly, from odor alone, that it’s going to taste horrible. Your nose knows what’s up, and that the last thing your body needs is a bunch of nasty bacteria in a gooey sweet sauce.

Smell, of course, doesn’t simply warn against spoiled food, it also increases your enjoyment of practically everything you consume. Much of what we commonly refer to as “flavor” is actually a combination of smell and taste, with taste most often assuming the secondary position. To prove it, try this simple experiment: Hold your nose, close your eyes, and try to tell the difference between red and white wine or between brandy and whisky served at the same temperature. In fact, without the sense of smell, most people aren’t able to tell the difference between grated apple and grated onion. Of course, this is because what we often call taste is in fact flavor. Flavor is a combination of taste, smell, touch, and other physical features like temperature.