Many people have probably wondered if the shiny oil on the surface of coffee bean is good or bad. The coffee bean contains considerable amount of fat just like other plants seeds such as corn, sesame, soy, nuts all do. The chemical structure of the coffee oil seems to be similar to cottonseed oil. Since cottonseed oil can be used for French fries, the coffee oil might cook great snacks for students studying all night for midterm.
Often the oil on coffee bean is said to be a sign of aging. When coffee bean is roasted to rather darker side, the shiny oil covering the bean becomes noticeable on its surface. From full city roast, subtle amount of coffee oil comes on the surface of the bean, and it is fully coated with shiny coffee oil at French/Italian roast. Even though it’s often seen as undesirable substance for the cup quality, but it’s actually a source of desirable flavor in a cup.
The amount of fat related substance in unroasted coffee bean is between 15% to 18%, and 80% of is is tryglyceride. The cafestol and Kahweol are the majorly known coffee related tryglyceride. It is a type of saturated fat that’s actually recommended by American Heart Association to reduce the intake of this substance. It does contributes to a high cholesterol. The oil contents in a cup varies depending on brewing methods. A paper filtered coffee has a minimal amount of it in a cup, on the other hand, the metal filtered brewed ones like french press and Able Kone, the amount of oil is much higher. I don’t know how much of it is actually in a cup. It is nice if that information is provided somewhere.
Even with risking some of your life expectancy, the oil containing essential flavor should not be omitted from coffee liquid. Through the heat adding roasting process, the fat is liquefied and vaporized. It oozes out as the oil from the crumbling bean surface. That’s how the darker roasts get shiny. The oil traveled through the internal structure of the coffee bean, so it collected flavor essence and generated high concentration.
Water Hardness, Brewing Method, and Coffee Oil
The contents of oil in a cup are based on a brewing device. The development of the brewing device has been heavily influenced by the water hardness. There seems to be a logical connection between the oil contents, water quality, and devices. In Europe, hard water is traditionally used for brewing coffee. As the result, metal filtered brewing methods represented by Espresso and French press have become mainstream. Those methods result high contents of coffee oil in a cup. Obtaining adequate body and sweetness is difficult with hard water, so dropping the flavor-enhancing-oil has been chosen through its history.
Oppositely, regions the soft water is supplied tend to go for a paper filter brewing. The major paper drip equipment manufactures such as Hario and Kalita are from Japan, where the soft water is widely available. The soft water is highly capable of extracting flavor elements from coffee grounds. In order to obtain adequate body and flavor, the extra coffee oil wasn’t necessary with the soft water. But interestingly, there is even a method to increase the amount of oil dropped into the cup.
When I make a serious cup, I blow off all the silver skin. It is obvious that removing the silver skin results a cleaner cup. However, considering what the oil does to the cup, silver skin might increase some flavor. I even heard some roasters saying the silver skin sucks flavor rich oil in. If that’s the case, keeping certain amount of silver skin adds positive flavor to the cup. It would be interesting to collect silver skin and brew it.
Photo: roasted coffee bean by jlodder