When you smell coffee brewing, you're processing the odor directly through your nose. The other route starts in your mouth. For example, when you eat an orange, you release volatile compounds in the orange. If you chew with your mouth open, some of these volatiles may reach your olfactory receptors via your nose. Other compounds, however, will reach the olfactory receptors in your nose through the backdoor, behind your mouth.
People vary in their ability to smell and taste.
Supertasters may have more than a thousand taste buds per square centimeter on their tongues and non-tasters less than 40. Hormones, such as estrogen, are thought to play a role in taste perception. Not only are women more likely to be supertasters than men, but taste perception tends to increase in women in response to high levels of hormones. For example, many women perceive bitter tastes more intensely during the first trimester of pregnancy. According to Valerie Duffy, a taste and smell researcher with the University of Connecticut, while we're born with a preference for sweetness and dislike for bitterness, our sense of smell starts out almost as a blank slate.