Biologically, how does this work? Well the answer it seems its still not 100% clear. Which is not surprising, considering the mysterious, intangible and evocative nature of aroma.
The pre-eminent theory is known as the Shape theory and this claims that smells are shapes, and an odour molecule will fit into a nasal receptor rather like a lock and key. Whilst this theory is widely accepted it still raises some inconvenient questions that cannot be answered by this theory alone.
The alternate and somewhat more radical theory is that known as Vibration theory. Vibration theory contends that odour molecules are perceived based on their vibrational frequency. Woah!
So while the research continues, the fact remains the same, that our sense of smell is powerful, evocative and wildly human.