What are Coffee Oils and Emulsions - Coffee Basics
A great espresso isn’t just extracted well, there's so much going on inside your cup, from how it's grown, roasted, brewed. You might be think it's just coffee and water inside your espresso but what you’re actually drinking is a brief suspension of coffee oils, water, and countless tiny bubbles of gas which forms a thick velvety cream on top of your coffee.
That rich layer of crema, the silky texture and the way the flavour seems to hang around afterwards all comes down to lipids and emulsified compounds that most people never give a second thought to.
Understanding coffee’s oils isn’t just about chemistry. It’s about learning how texture, temperature and aroma interact to define how coffee feels and tastes.
Coffee as an Emulsion
At its core, coffee (especially espresso crema) is a complex suspension and emulsion. Water acts as the solvent, extracting oils, gases, and soluble compounds from ground coffee. Those oils, primarily lipids and triglycerides, are dispersed into tiny droplets, suspended by surface tension, pressure, and naturally occurring surfactants.
This mixture of oil and water is temporary, like shaking a vinaigrette. The moment the shot ends, the emulsion begins to collapse. That’s why espresso’s crema fades, and why filter coffee brewed at atmospheric pressure, looks clear and has a significantly lower amount of oil by comparison.
What Are Coffee Oils?
Coffee oils come primarily from the lipid fraction of the green bean, which accounts for about 10-15% of its mass. These lipids include triglycerides (molecules made from glycerol and fatty acids), as well as diterpenes (cafestol and kahweol), sterols and waxes.
During roasting, the bean’s internal structure expands and microfractures, releasing these oils toward the surface. This not only affects appearance (oily vs dry beans) but also chemistry:
- Light roasts: Oils remain mostly locked inside, preserving clarity and crisp acidity.
- Dark roasts: Heat drives oils outward, increasing perceived body but also increasing oxidation risk when stored poorly.
These oils carry many of coffees aromatic and mouth coating compounds. They are the transport medium for volatile molecules that define flavour persistence, depth and tactile richness.
Crema Formation in Espresso
Espresso extraction is a symphony of fluid dynamics and chemistry. Under roughly 9 bars of pressure, hot water and superheated CO2 from freshly roasted coffee interact to suspend oils, gases and microscopic solids in the liquid.
This is what instantaneously happens when you pull a shot of espresso:
- CO2 gas expands as water hits the coffee puck.
- High pressure forces lipids, surfactants and soluble solids into dispersion.
- Surface-active molecules such as amphiphilic proteins, polysaccharides and melanoidins, help stabilise these droplets, forming a transient microemulsion.
- The crema emerges: a foam layer of micro bubbles coated in oils and natural surfactants rise to the top of the poured espresso shot.
This is why espresso appears opaque and creamy, you’re literally drinking billions of suspended oil droplets and micro bubbles in a short-lived emulsion.
Crema Stability and Why It Fades
Crema is a delicate foam made of CO2 micro bubbles surrounded by oils and surfactants. But it’s inherently unstable, a structure constantly fighting gravity and gas diffusion.
- Gas diffuses out, causing bubbles to expand and pop.
- Surfactant depletion weakens the bubble walls.
- Heat accelerates lipid oxidation and drainage, thinning the foam.
Robusta coffees often produce higher crema volume due to more soluble solids and gas retention, while Arabica typically contains more lipids, which can yield finer but more transient crema. The difference isn’t strictly about quality, it’s about the balance between CO2 release, oil composition and roast freshness.
Crema longevity should be seen as a reflection of chemistry, not quality. A delicious tasting espresso can have next to no crema left and still deliver exceptional flavour.
Oils and Mouthfeel
Oils define how coffee feels. They don’t directly add sweetness or acidity but they can shape the texture and your flavour perception.
- More oils = richer, heavier body.
- Fewer oils = cleaner, brighter profile.
Lipids coat the tongue, softening sharp acidity and bitterness while amplifying roundness and persistence. This is why espresso feels dense and syrupy, while pour over coffee feels delicate and transparent.
Oils also influence aftertaste, they hold aromatic compounds that linger after swallowing. The longer they stay suspended, the longer coffee’s sensory “memory” lasts on the palate.
Chilled Extraction and Aromatic Preservation
Temperature dramatically influences how oils behave. Warmth enhances aroma release but also accelerates oxidation. Cooling slows this process, preserving balance between volatiles and lipids.
This principle underlies tools like the Coffee Alive Chilling Ball, rapid cooling after extraction can reduce oxidation and volatile loss. While peer-reviewed research on chilled espresso remains limited, early sensory results and physics strongly support its benefits: a fresher, more layered flavour even hours later.
Cold extraction methods (like cold brew) operate on the same thermodynamic logic, slower oxidation, higher lipid retention, smoother mouthfeel. Chilled espresso simply applies that balance to a pressurised brew, helping preserve crema and aromatics that normally dissipate within minutes.
Read more about Extract Chilling Coffee.
Oil in Filter Coffee
When you brew a pour over or batch brew, you might notice how clean and transparent the cup looks compared to espresso. That’s not just clarity, it’s chemistry. Filter coffee contains far fewer oils because the brewing process happens under atmospheric pressure, not the high pressures that emulsify lipids into espresso.
Paper filters, in particular, absorb a large portion of these oils. That’s why filter coffee tastes lighter, crisper, and sometimes even tea-like. The oils that do make it through are primarily smaller lipid droplets and diterpenes, compounds like cafestol and kahweol, but in much lower concentrations than espresso.
This difference is part of what defines filter coffee’s character:
- Less oil means less viscosity and mouth-coating texture.
- More selective filtration means higher perceived acidity and clarity.
- Reduced lipid presence also extends the cup’s flavour stability, oils are prone to oxidation and can go rancid over time.
Interestingly, brewing with cloth filters like the Aji Filter retains a fraction more oil, adding subtle body and a rounder mouthfeel without the heaviness of metal filter brews. Metal filters, on the other hand, allow nearly all oils to pass, producing a cup that feels closer to immersion-style brews or even light espresso.
In essence, filter coffee reveals the flavour of solubles, while espresso expresses the flavour of emulsions. Both are authentic representations of the same bean, just expressed differently due to the way it was brewed.
Practical Brewing Implications
Different brew methods manage coffee oils in different ways and that directly affects taste. When discussing oils in filter coffee, a large part of this has to do with the coffee filter you use when brewing.
- Paper filters from brands like HARIO, CAFEC and Sibarist absorb oils and lipids, resulting in a cleaner, more delicate cup with greater transparency.
- Metal filters like the AeroPress metal disc or espresso baskets allow oils to pass through, creating more texture, weight and lingering aromatics.
- Cloth filters like Aji Filter strike a middle ground, retaining some oils for body, while filtering enough for clarity.
Each variable adds to the tactile identity of how your coffee tastes. The 'best' filter or 'best' amount of oil in your coffee depends on whether you’re chasing clarity or richness and this largely depends on your preference. There is no right answer here, only opinions on what tastes better.
Coffee’s oils and emulsions are where chemistry becomes texture. They bridge the invisible world of molecules with the sensory one of taste and feel the difference between clarity and weight, between fleeting aroma and a cup that lingers. Espresso’s crema, pour over’s transparency, even cold brew’s silkiness are all expressions of how lipids and water negotiate balance and how this translates to your cup.
By understanding oils in coffee, baristas can better preserve what makes coffee taste alive. With aromatic integrity, tactile harmony and balance between clarity and body in the cup.
