How The Brain Interprets Coffee

How The Brain Interprets Coffee

Do you remember the first time you tried coffee? Can you remember the taste? The decadent aroma?

Some people do. They say they don’t like it, “it’s too bitter”, or “too strange”. Then something miraculous happens inside the brain and people grow to love it. Nearly every food is like that, with an initial period of dislike, followed by a change in preferences, although you may not remember it.

That’s because like nearly everything else in life, flavor preferences have to be learned. Exposure determines your preferences, with the exception of sweetness (a love of sweet foods comes pre-built in the human body). Everything else is earned through experience.

Why is that?

How come you don’t come out of the womb liking certain foods?

Why don’t babies enjoy lemons, coffee, and avocado the first time they try them?

A Natural History

If you look at the genes that seem to code for the perception of certain flavors, you’ll find all sorts of interesting mechanisms lying dormant:

“The human genome is littered with the rusting hulks of bitter receptor genes that no longer function.”
Flavor: The Science of Our Most Neglected Sense¹

I’d like to think those receptors as a chemical arsenal of tools hard-earned by our ancestors in a long war for survival.

I say “survival” because in nature, bitterness sometimes translates to “poisonous”. Not always, but often enough that the organisms that developed a taste for bitterness survived and passed their genes down to us. The myriad of genetic receptors for bitterness is a testament to that.

So the first time you try coffee with no cream and no sweetener (the very first time) your brain rings warning bells. It’s a false alarm, because coffee won’t kill you (some even say it improves your health). But the brain needs some data and some time to figure out whether coffee is dangerous.

So you go to bed, and the brain does something miraculous: It learns.

We don’t know exactly what goes on in the brain when it dreams or learns. It’s complicated to say the least. The construction of the bitter receptor sites in your mouth alone is unusual and unlike anything you’d see in an engineering class.

Genes program three-dimensional structures from scratch in a water-based medium, using massive parallelism and swarm programming while making use of, and being constrained by, the laws of physics and chemistry.

Quanta Magazine, Solution: The DNA Computer Program

Still, we have approximations for what may be going on after you try coffee for the first time. For one, it seems like the brain can differentiate between a food with some calories and no calories over a few weeks. Over time, your brain will get a sense for “high-calorie” foods and “low-calorie” foods, although not in those terms exactly. Flavor it turns out is inextricably tied to calorie count.⁵ You don’t like a french fry because it tastes like a delicious french fry. It’s the other way around: It tastes like a delicious french fry partly because it has a lot of calories. The same goes for coffee with sugar and cream.

But the weird thing is that many people who like coffee black, without cream and sugar, drink it despite the lack of calories. Why is this?

When the brain constructs the flavor profile of a food, it isn’t just conceptualizing the calorie content. It’s also inferring its chemical composition and the effect it has on your body.

It’s unclear why precisely the brain loves the feeling caffeine gives. Perhaps the brain notes the increased levels of focus and infers the benefits are substantial, so much so that it doesn’t mind the lack of calories.

Second Plate

It’s the second day and your brain has changed. You decide to give that coffee another go. But this time, it tastes different.

Flavor is interpreted through the lens of memory, changing your experience of the coffee you had last night. Safe food is good food. On the second day, your brain has taken new liking to coffee and other “notes” begin to pop out.

When people think about flavor, they mostly think the tongue is doing all the work. But that’s an illusion. Smell matters too. Humans have specialized olfactory senses in the cavity of the mouth, a cavity that seems designed to aerate the odors of food so whenever you breathe out, molecules flow right into your olfactory epithelium (small band of neurons about the size of a quarter resting in your nasal cavity).

Most of what we think of flavor is actually a combination of taste plus scent. It’s why rosemary makes steak tastes better, why chili’s taste spicier whenever you breathe out, and why food doesn’t taste as good when you have a stuffy nose. Your brain uses scents just as much (if not more) than what your tongue touches to create the experience we call flavor.

Humans are unique in that respect in the animal kingdom. According to Gordon M. Shepherd, Homo Sapiens have the greatest capacity to detect smells inside our mouths out of all the organisms in the animal kingdom.⁶

A dog, with its extraordinary nose, finds the way to the butcher much faster than we do; but the sausage does not taste so good to it.
— Rolf Degen

And it’s this remarkable ability that allows humans to perceive the molecule that makes coffee smell so great: Furfuryl mercaptan.

Open up a bag of freshly roasted coffee and take a deep breath — that wonderful aromatic smell owes its existence to furfuryl mercaptan.

Its importance shouldn’t be understated. Furfuryl mercaptan doesn’t just make coffee smell like coffee — it’s what makes fresh coffee taste like fresh coffee. Without furfuryl mercaptan, coffee would taste alien and stale. You’ll know it whenever you make an old batch.

It’ll lack a distinct freshness.

Where does furfuryl mercaptan come from?

It comes from the Maillard reaction, traditionally known as the “roasting” process. Kenji from the Food Lab gives a good overview:

“Named after Louis-Camille Maillard, the scientist who discovered it, the Maillard reaction is the complex series of chemical reactions that causes foods to brown…Although Maillard reactions can occur at relatively low temperatures, they are glacially slow until your food reaches around 350°F…To this day, the exact set of reactions that occurs when Maillard browning takes place has not been fully mapped out or understood. What we do understand is this: it’s darn delicious. Not only does it increase the savoriness of foods, but it also adds complexity and a depth of flavor not present in raw foods or foods cooked at too low a temperature. That’s why your steak tastes so much meatier when it’s properly browned, and that’s why for most people, the outer crust of the meat is the tastiest part.”
— The Food Lab: Better Home Cooking Through Science³

Once the coffee beans are roasted, it generally takes a few days to a few weeks before the molecules vanish enough to notice the change in flavor. This is because carbon dioxide inside the coffee beans slows down the oxidation process. Like the rusting of iron, coffee beans experience oxidation effects that slowly erode the molecules inside. But the process is slow. Coffee beans will store for a good while before going bad. It’s only when you grind coffee beans that the oxidation process goes into overdrive.

That’s not necessarily a bad thing. Like the Maillard reaction, grinding creates a bunch of new molecules that also makes coffee taste fresh, but they’re volatile compounds (they don’t last long). Some researchers have described them as “ rich in nutty and smoke-roast aromas”.⁷

There’s also another downside. You know that all that delicious furfuryl mercaptan you acquired during the roasting process? Well, by grinding the beans, you’ve exposed more of it to the air, where it’ll rapidly disintegrate.

It’s why grinding coffee beans, then storing that grind for a few days is a poor solution. As any experienced coffee drinker will tell you, there’s a world of difference between coffee with freshly ground beans versus beans that were roasted days ago.

It’s chemistry.

The Most Essential Ingredient

The ability to smell is an ancient mechanism.

It’s so old, when you take a bite of something to eat, the odors from the food go through the limbic system first, where emotion and memory reign supreme⁴.

Smells from the mouth then combine with “data” from the tongue to paint a picture designed first and foremost to keep you safe. It’s an important activity. It is, in a way, the most important activity.

When you eat, you activate more parts of your brain than just about any other activity. You’re adapted to analyzing food, its chemistry and caloric count. We are, in a sense, a kind of chemistry lab built to detect the composition and effect of molecules.

In that respect, time is the most essential ingredient.

It’s time that pushes the oxidation process of coffee beans to ripeness, time that alters the chemistry and perception of flavor. It’s time that allowed for the evolution of the bitter and olfactory receptors that can capture the complex notes of a fresh batch of coffee. And it’s time that makes it so difficult to capture something like furfuryl mercaptan at its height.

The universe is in constant flux. If you’re not quick enough, a landscape of experience will fly right by. Like a photographer capturing the finish of a race, so must the coffee brewer capture a specific moment in time, when the molecular puzzle pieces finally line up, and all the notes and colors come together.

This blog post is sponsored by Bottomless, a coffee delivery service that uses a smart scale to predict and ship when you’re low on coffee beans .

Never run out of furfryl mercaptan again.

¹ Holmes, Bob. Flavor: The Science of Our Most Neglected Sense (p. 23). W. W. Norton & Company. Kindle Edition.

² Ibid. (p. 169)

³ López-Alt, J. Kenji. The Food Lab: Better Home Cooking Through Science . W. W. Norton & Company. Kindle Edition.

⁴ Holmes, Bob. Flavor: The Science of Our Most Neglected Sense (p. 5). W. W. Norton & Company. Kindle Edition.

⁵ Ibid. (p. 134)


Andrew Ruiz

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