Roasted coffee beans’ appearances can vary from shiny to dull. Some beans have a glistening sheen, while others show a fully matte finish. The difference is caused by oils. Here’s a look at what causes coffee beans to be oily or dry.
In This Guide:
- What Causes Some Coffee Beans to Have Oils?
- Why Are Some Coffee Beans Oily, and Others Dry?
- Does Oiliness Affect the Taste of Coffee?
- Are Dark Roasted Coffee Beans Always Oily?
- Are Oily Coffee Beans Stale?
- What Are the Best Ways to Brew Oily Beans?
- Tips to Find Dry/Non-Oily Beans
- Will Oily Beans Clog Your Grinder?
- Will Oily Beans Clog Your Automatic Coffee Maker?
- Oily Beans and Super-Automatic Coffee Makers
- Which Are Better, Oily or Dry Beans?
What Causes Some Coffee Beans to Have Oils?
Coffee beans are the seeds of the coffee tree, and they thus have lipids (fats) just as most seeds do. Lipids are a compact way to store the energy that new plants need when germinating.
Approximately 7% to 17% of a coffee bean’s weight is from lipids, and specialty-grade arabica beans tend to be toward the higher end of this range. Any oils on the surface of coffee beans are these lipids leaching out. The oils that you might see on coffee beans develop when those lipids leach and then oxidize as they come into contact with oxygen.
Understanding that oils are the product of oxidized fats that naturally occur in coffee beans helps make clear the whole issue of whether coffee beans should be oily or dry.
Why Are Some Coffee Beans Oily, and Others Dry?
Whether coffee beans appear oily or dry depends directly on how many oils currently coat the surface of the beans. Coffee beans that look oily have lots of oils on their surface, while those that look dry have few or no oils on the surface.
There are three primary factors that impact whether the oils that are in all coffee beans come to the surface:
Some coffee varietals/cultivars naturally have more oils than others. A bean that has 17% lipids is going to appear more oily than one that has only 7% oil, regardless of any other factors. There’s just so much oil in the high-percentage bean that some invariably leaks out.
There’s no strict rule as to which varietals have higher oil contents and which have lower ones. As a general guideline, green (pre-roasted) coffee beans that look dark tend to have more oils than those that look light.
Dark roasts look more oily than light ones, because oils are drawn to the surface of the beans during the roasting process. The difference in oiliness is especially noticeable between roasts that don’t reach the Second Crack (light and medium roasts), and those that go to or past the Second Crack (dark roasts).
The Second Crack releases carbon dioxide from the beans, which forcefully opens the beans up more. Oil then quickly leaks out to the surface through the openings that escaped carbon dioxide created.
In beans that aren’t oily due to their varietal or roast level, oiliness is an indication of how fresh or stale the beans are.
Oils will slowly leak out of any coffee bean, and then they’ll eventually dry. An oily sheen thus indicates that beans aren’t immediately fresh, but also that they aren’t completely stale. The oils will evaporate and be gone by the time coffee is completely stale.
Does Oiliness Affect the Taste of Coffee?
The oiliness of a coffee bean indeed has a direct impact on taste, but not necessarily how people expect.
The oils in coffee beans are largely responsible for the bean’s terroir (natural flavors), and thus oils are very desirable in specialty coffee. The fine notes that make high-grade coffees distinctive are lost once all of the coffee’s oils are lost. Trapping the oils in the brewing process will bring out the most flavor from the coffee.
As mentioned above, oils are also an indication of how fresh coffee beans are. Beans that appear oily still have at least some oils in them, and should produce decent brews at a minimum. Beans that are mostly dry may have been recently roasted, and they might need to degas or might make extremely vibrant brews. Beans that are completely dry with no hint of oils have gone stale.
Are Dark Roasted Coffee Beans Always Oily?
Dark roasts typically take coffee beans beyond the Second Crack during the roasting process. The Second Crack is a specific stage, at which beans “crack” akin to popcorn popping. The stage indicates that beans have reached an internal temperature of ~224°C (~435°F).
The crack of Second Crack is carbon dioxide leaving, which creates pores on the surface of the beans for oils to leak out.
As a result, all dark roasted beans will appear more oily than their light roasted counterparts. The difference is especially striking immediately after roasting. This is before the surface oils have evaporated on the dark beans, and the internal oils have leached out on the light beans.
Are Oily Coffee Beans Stale?
Oils on coffee beans generally aren’t a sign of the coffee being stale. If you can see how dark or light a roast is, however, they can serve as a general indication as to how fresh the coffee is.
Dark roasted coffee beans are oily immediately after roasting, because they reach the Second Crack during roasting (see above). Oils on the surfaces of these beans isn’t an indication of staleness at all. Instead, dry dark roasted beans are quite stale. They’ve sat long enough for all of the oils on the beans’ surfaces (and inside the beans) to evaporate.
Light roasted coffee beans aren’t oily immediately after roasting, because they’re cut off before the Second Crack. As the oils that remain within these beans, the beans will gain a sheen.
Light roasted beans that are pretty dry are extremely fresh. They might be only a few days, or at the most a couple of weeks, old. These are when the beans taste best, provided they’ve had time to sit and are degassed pre-brewing.
Once the oils that remain within light roasted beans leach to the surface, the beans are several weeks or a couple of months old. Although they’re not technically quite as fresh, they’re still considered “freshly roasted” and will make great brews.
The oils on these beans will still provide good flavor in the cup. Cafes will brew the beans because the flavor is good, and because they don’t want to sustain the cost of throwing the beans out. Few home baristas, and even the majority of professional baristas, won’t sense a noticeable difference between these and fresher beans.
Once light roasted coffee beans are completely dry, any oils in them have leached out and evaporated. These beans are stale and will have dulled taste. They’re at least several months old, and could have sat for a year or longer.
In short, any coffee beans that are oily aren’t stale and should be brewed. Both dark roasts and light roasts will taste good if the beans are still oily
What Are the Best Ways to Brew Oily Beans?
Any brew method will work well with oily coffee beans, and you’ll likely find that they taste great with your preferred brew method.
Basic Brewing for Oily Coffee Beans
If you would like to trap the flavors that are present in the oils, however, a method that doesn’t use paper filters is preferable. Paper filters absorb the oils that are in coffee. Metal filters don’t, so the oils end up in the brewed coffee. A metal filter will produce the most vibrant cup from an oily coffee.
The French press is perhaps the most iconic non-paper brewing method, and espresso also doesn’t use paper filters. Metal filters are available for most manual pour-overs and automatic drip brewers, too.
Advanced Brewing for Oily Coffee Beans
Oily coffee beans will extract differently than dryer (non-stale) ones. The difference doesn’t stem from the oils themselves, but rather the minuscule passageways that the oils leached out through. If oils can leach out easily, then water can leach in easily.
More water entering the beans increases extraction rates, and thus you can counteract this by decreasing extraction. You might try brewing for slightly less time, and/or grinding slightly coarser. Either adjustment will slow extraction slightly.
Note on Brewing Dry, Stale Coffee Beans
Coffee beans that look completely dry are likely stale, and will produce dull cups of coffee. These beans are well-suited for cold brew, which doesn’t extract all of the flavors in coffee bean oils anyway. Stale beans can also be used in baking (e.g. for tiramisu).
Tips to Find Dry/Non-Oily Beans
If you want dry beans that aren’t too oily, look for light roast levels and freshly roasted coffee. Any light roast will have fewer oils on the surface of the beans than a darker roast. Any bag that has a “roasted on” date is freshly roasted, and won’t have allowed too much time for oils to leach out.
You can further delay beans from becoming oily, by storing them in an airtight container. The bag they come in works well if it has a one-way valve and is kept tightly closed. You also can use an airtight canister.
Will Oily Beans Clog Your Grinder?
A few bags of oily beans shouldn’t clog your coffee grinder, and they’ll actually go through your grinder more easily. The pores that are in oily beans make the beans more brittle, so they grind easier.
Constantly grinding oily beans may create a buildup of coffee oils on your grinder’s mechanisms. Most grinders can be disassembled, which allows you to wipe any oil buildup off of the burrs. Use a lint-free cloth (or a coffee filter) to wipe up the oils.
Will Oily Beans Clog Your Automatic Coffee Maker?
Oily beans won’t cause any problems for automatic coffee makers. Paper filters will trap the oils, or they’ll slide over metal filters without a problem. Enough water is used during brewing and basic rinsing/washing that the oils won’t build up on a metal filter.
Oily Beans and Super-Automatic Coffee Makers
Some fear that oily coffee beans will clog superautomatic coffee makers. In my personal experience, this might be a theoretical fear but doesn’t play out in the real world.
The theory claims that excessive oils will build up and clog superautomatic machines. Non-oily beans that are freshly roasted still have a comparable number of oils in them, though, and thus would theoretically also clog super-automatic makers. If there’s a fear about oily beans, there would logically be the same fear over dry fresh beans.
In 20 years of professionally working in coffee shops and writing about coffee (including selling superautomatic machines), I’ve never actually heard of a customer reporting this problem. Moreover, these machines don’t come with warnings against using dark roasted beans that are oily.
Anyone who’s concerned about oily beans clogging their superautomatic coffee maker should be further reassured by the cleaning cycle. All of these machines have a cleaning cycle that’ll remove oil residue within the machine.
Which Are Better, Oily or Dry Beans?
Neither oily nor dry coffee beans are inherently better. Instead, understand how varietal, roast level and freshness impact how oily beans appear. Like so much with coffee, learning about this particular aspect of coffee will help you better choose coffees that you prefer. Those might be oily or dry coffee beans, depending on your preference.
If you are interested in roasting your own coffee beans at home, take a look at our guide.
Scott M. Brodie has over 20 years of professional experience working in coffee shops and writing about coffee (including selling superautomatic machines). When not writing, he can usually be found roasting a new African single origin or composing a fictional work.