In Flavor, Part 1, we talked about the tongue's role in perceiving flavor. Now we discuss the nose's role.
When we talk about flavor, we typically think only of our tongues, but flavor is comprised of two sensory systems: the tongue, where perceive taste, and the nose, where we perceive aroma. Thanks to our bio-diversity, we all sense things a little bit differently, which often leads to a wide range of opinions on your favorite beer.
Your nose has a huge influence on how flavor impacts you, as you'll notice the nose's influence right way when it's clogged thanks to a cold and everything tastes bland: taste and aroma are best friends that give us flavor.
The tongue only perceives basic tastes: salty, sweet, bitter, sour, and umami (or savory). This is where the nose comes in, because everything else we attribute to flavor (aside from texture) is actually aroma perceived by the nose.
Most humans have around 9 million olfactory neurons that exist between the upper part of the nasal cavity and the back of the throat; we're lightweights compared to other animals like dogs who have around 225 million. We use aroma to try to identify not only something good, or beneficial, but also something rancid or unappealing. Aroma data is perceived by some of the oldest parts of our brain: from the hypothalamus where we process appetite, anger, and fear, to the brain stem, which controls basic regulatory body functions.
The nose has two sensor systems: the ortho-nasal and the retro-nasal. The ortho-nasal sensors are high up in the nose and they're used to analyze, categorize, and identify aromas when you breathe in. These sensors come into play when you stick your nose up to that IPA and get a good whiff of that piny goodness.
The retro-nasal system sits in the soft tissue at the back of your mouth and in the channel that connects your mouth to your nose; it perceives aromas more as flavor when you breath out while food is in your mouth. The retro-nasal sensors are also connected to preference, familiarity, and satiety. When you taste something and it reminds you of Band-Aids, you're seeing your retro-nasal sensors at work.
As you chew your food, many things happen to release new and more aromas into the retro-nasal channel; this is why just smelling something doesn't reveal the entire flavor profile and the two are sometimes almost at odds, such as being repulsed by the ortho-nasal aroma of smelly cheese versus putting it in your mouth.
When you chew, the food warms up, you increase the surface area of the food, and things like bubbles are bursting, which all contribute to the nasal bouquet that is sent to the brain for computation. All of that sensory data is then combined with taste to produce what we all call flavor.