There are two different smells that humans perceive -- the smell of inhalation and the smell of exhalation. The scent experienced when you inhale, with food in front of you, is referred to as orthonasal olfaction. It occurs when you sniff through your nose. Conversely, when you take a bite of food and chew it, the aromatic substances from the back of your throat enter your nasal passages along with your exhaled breath. Science writer Bob Holmes explains that the human throat is specifically designed to guide these odors into the hollow of the nostrils. The air entering through the nose forms a barrier, resembling a curtain, in the throat, which prevents aromatic substances from the mouth from reaching the lungs. As a result, when we consume food and chew, our attention is solely directed toward the smell of our exhaled breath. While dogs possess a remarkable sense of smell, humans actually have an even more advanced ability when it comes to perceiving exhaled odors. Dogs have elongated noses that are optimized for orthonasal olfaction, but humans possess a well-developed retronasal olfactory system. The retronasal smell is a unique capability exclusive to humans.

Once you understand the anatomical structure of humans, it's easy to see why we love foods that smell bad. For example, a hotpot prepared with well-fermented hongeo (skate) can elicit a potent and pungent sensation in the nose. But when you bite into it, it tastes rich and refreshing. Yonhap News reporter Kim Jin-bang, a foodie well versed in Chinese food, describes it as “stinky on the outside, but clean on the inside.” Another similar example is durian. Despite its repulsive odor to the nostrils, the experience of consuming durian is quite the opposite. Once you taste its sweet and creamy texture, you begin to understand why it has earned the title of "king of fruits.” It's the same reason you're drawn to cheonggukjang stew, made with fermented soybeans, even though you're worried about stinking up your clothes. On the flip side, like the aroma of freshly brewed coffee, what smells great on the nose can taste like a bland flavor on the palate.

Paul Rozin, a renowned food psychologist, was the first to notice that food smells different when you put it in your mouth than it does before you do so. He noticed that the foul odor of Belgian Limburger cheese vanished when he put a piece of cheese in his mouth. Even after Rozin documented this observation in the 1980s, it was challenging to prove it scientifically. It's not easy to tell which part of the mouth is the olfactory system, as we experience not only the smell of food, but also its touch and taste. It wasn't until elaborate experiments in which tubes were inserted and people were asked to smell individually from the orthonasal and retronasal olfactory tracts that Rozin's hypothesis was finally confirmed.

Many people avoid foods like cheese and hongeo because they smell bad. They may even despise or look down on people who enjoy these foods. However, the smell of the retronasal olfactory system is where the flavor comes from. Remember: the only way to find out what a food really tastes like is to let go of your preconceptions and put it in your mouth.

Jeong Jae-hoon is a food writer and pharmacist. He covers a variety of subjects, including trends in food, wellness and medications. This column was originally published in Korean in Joongang Ilbo on May 25, 2023. – Ed.