Why Do Roasted Coffee Beans Develop Oil Spots?

If you’ve started to roast your own coffee beans at home, chances are, you’re enjoying some of the finest coffee you can get your hands on.

But if you’re a beginner, there are a variety of problems you might face during your journey towards expert roaster. One of which might be that your coffee beans are starting to develop oil spots.

Whilst it’s not an inherently bad thing to have oil on the surfaces of your coffee beans (it’s fairly common with darker roasts). However, the oils in coffee are volatile, so the more they are exposed, the faster they are lost and become rancid or stale.

You lose flavours and greasy beans clog grinders a lot easier as they coat everything in their oils. So why is this happening for your roast? We asked expert coffee roasters Taylor White for more information.

Why do roasted coffee beans develop oil spots?

Oil spots are just a sign that your roast got pretty hot, either to second crack or near it. There is oil in all coffee beans but it’s trapped inside the bean structure inside the cells. When you get around second crack, the bean’s cellulose structure begins to fracture/break apart.

The heat and pressure forces all of the stuff in the cells, including the oils, out through the openings made because the structure is fractured. Due to all of that the oil travels outwardly. It will continue slowly after the roast is done, if things have been broken up enough.

The oil will travel to the surface like you’re seeing. Note that compared to beans with no oil on the surface, beans with oil on the surface will stale faster.