The lipids of coffee play an important part in the storability of roasted coffee. During storage the lipids can be oxides if oxygen is present and it changes the aroma of coffee, too.
The total lipid content of coffee varies with the species from about 7 to 17%, with average values of about 15% for arabica and 10% for robusta types.
The largest fraction consists of liquid coffee oil, which is found in the endosperm. Coffee oil is composed mainly of tricylglycerols as well as fatty acids in similar quantities to those found in common edible vegetable oils. About 0.24% (i.e. between 1-2% of the total lipid) is referred to as ‘coffee wax’.
Diterpene esters 18.5%
Free diterpenes 0.4%
Sterol esters 3.2%
Free sterols 2.2%
Carboxylic acid-5-hydroxytryptamides 0.6-1.0%
The main free fatty acids in the oil are linoleic acid (43-46% of the acids) and palmitic acid (30-35%). Oleic, stearic, arachidic and linolenic acids are also present in lower proportions. The presence of free fatty acid is evidently the most important factor affecting flavor formatting during roasting.
Both green and roasted coffee oils are used industrially, the former in the cosmetic industry and the latter in food applications such as flavorings.