What are lipids in coffee?

Lipids are the fats and oils found in coffee beans, making up approximately 15-17% of the dry weight of Arabica green coffee (Robusta contains less, around 10%). In the green bean, lipids are concentrated in the endosperm and protected by a waxy outer layer; during and after roasting, they migrate to the bean surface as the cell walls break down - which is why darker-roasted beans appear oily and shiny.

Lipids play several important roles in coffee quality. They are carriers of flavour compounds and contribute to the perceived body and mouthfeel of brewed coffee, particularly in espresso where the high-pressure extraction captures more lipid content than paper-filtered brew methods. The characteristic richness and coating sensation of espresso is partly attributable to emulsified lipid droplets in the extraction.

The flip side of coffee's lipid content is rancidity. Coffee oils are susceptible to oxidation - once exposed to air, they begin to degrade into off-flavours including rancid, stale, and cardboard notes. This is one of the primary drivers of roasted coffee going stale: the lipids on the bean surface and within the broken cell structure oxidise progressively after roasting. Whole beans stale more slowly than ground coffee because grinding dramatically increases the surface area of lipids exposed to oxygen. For green coffee, the waxy outer layer of the bean protects lipids from oxidation, contributing to green coffee's significantly longer shelf life compared to roasted.