Oily coffee beans are subject of heated conversation, everyone has their own thoughts about them. Coffee Brewing Methods has a post on the topic, an intriguing perspective. Here is our understanding of the subject as Coffee Brewing Methods introduces it.

Dark roasted beans have a more breakable shell due to their prolonged exposure to heat during roasting. The more we expose the beans to high temperatures, the more they grow in size and lose consistency. The oils are pushed out from the inside. This means that beans will lose flavor faster and leak oil quicker. On the other hand, a lighter roast will hold the coffee oils and the sugars inside. They will just be drawn out during coffee preparation, when exposed to hot water.

Oily Coffee Beans – What Does It Mean?

This is a very discussed subject, and again not fully understood. Oily beans are not necessarily a bad thing. I heard people blaming oily coffee for poor brewing results, and some people even saying that coffee was rancid because of the oil.

None of these are true. The oil in the coffee beans is very important for the end result of the brew. Coffee beans contain oil which is released in the roasting process with the darker roast. Without the oil in the beans, espresso would have no "crema", the foamy layer would be nonexistent. A lot of the aromas and flavors of the darker roast beans come from the oils. So oil in the beans is normal.

Why are some coffee beans shiny?

During the roasting process, gases and oils are extracted from the coffee bean. The longer the beans are roasted for, the oilier they are. This is the reason that dark roasted coffee beans will normally be oily. So now we can already state, at this early point in the article, that an oily coffee bean is neither good or bad: it is simply a typical property of dark roasted coffee beans.

Dark Coffee Beans Not Oily

Note that coffee beans are very darkly roasted but they are not shiny. Beans are either very fresh, or too old.

Why don't We Always See the Oils if it's Normal?

Depending on the roast level, the oils start to surface the coffee bean between 3d day and three weeks. So you could have beans roasted 2 weeks ago and see no trace of oils, yet the oils are there, they just didn't surface. There is a saying that if there is no oil on the beans, the coffee is either too young or too old.

The presence of oils is not indicative of a stale batch, but rather an indication that the batch should be consumed fast, because of the lower shelf life of the dark roasts. After the oils are released, the shelf life gets very short, since the oils start to evaporate the minute they surface the bean.

Important note: The darker the roast the faster the oils get to the surface. Spanish roasts bring the oils out from the first day after roasting.

Important note: The oils are released in the roasting process after the second crack. So roasts that don't involve a 2nd crack will be oil free.

Source of the article: oily coffee beans