That’s right, whoever smelled it…knows exactly what I’m talking about.
Odors come from light, volatile molecular compounds which travel through the air to your nose. Receptor cells in the nasal cavity help us distinguish smells and then transfer information about those smells to our brain. Thus, our sense of smell may conjure up a Thanksgiving-sized appetite, or might prevent us from sniffing (or worse – consuming) back-of-the-fridge dairy products. As humans, we’re able to identify thousands of smells, some in very small amounts.
According to many, our sense of smell is the most powerful driver for how we recognize and perceive flavor. The unforgettable potency we know to be rotten eggs is thanks to sulfur compounds, which are also behind the aroma in onions, garlic, and horseradish. Roasted nuts, green peppers, coffee, and chocolate all gain their smells from pyrazine (nitrogen-containing) compounds. Blue cheese and butter owe their familiar smells to ketones (methylamyl ketone and diacetyl, respectively). Other smelly compounds may have aldehyde, ester, alcohol, or thiol, derivatives. Compounds with lower molecular weight have more intense aromas.
Remember drawing those hexagonal ring structures back in chemistry class? (You were mumbling “when am I ever going to see this again?”) Many recognizable aromas are initiated by ring structures with carbon, hydrogen, and oxygen components. Here’s an example:
Source: Genevieve L. Christen, ed and J. Scott Smith, ed. Food Chemistry: Principles and Applications. Science Technology System, 2000