Bacon’s mouth-watering smell comes from the meat’s amino acids and sugars reacting to heat. Known as the Maillard reaction, the process releases hundreds of compounds associated with desirable aromas and flavours, resulting in a complex assault on our senses. Our brains have evolved to recognise these smells as good, presumably due to the survival advantage that heating food had for our ancestors. The Maillard reaction also happens when you toast bread or roast coffee beans, although different compounds are given off. Some of the compounds have similar characteristics and are often described by food scientists as nutty, smoky and caramel-like.
Answered by Rik Sargent.