Think you know the fresh, lemony taste of lemongrass, or the lush herbal taste of basil? Most of what we experience as "taste" actually comes from our sense of smell, not from our tastebuds. Volatile compounds — molecules light enough to produce a vapor or gas — play a key role in how we experience food and drink (as well as fragrances and scents). But the complex ways in which we perceive these molecules as flavor is not nearly as straightforward as pure chemistry, making understanding flavor partly, but not completely, a chemical question.
Using a gas chromatograph-mass spectrometer (GC-MS), a laboratory instrument that separates and detects the concentrations of mixtures of volatile compounds, we can easily quantify the aroma molecules in, say, a cup of coffee. But we still can't ascertain which of these molecules are most important to its overall flavor, be it nutty, chocolatey, or fruity.