What is Tiger Stripe Espresso? Where Does Espresso Crema Come From? How Do Fine Grinds Affect Coffee?

What Are Those "Oil Spots" on Espresso Crema?

Today, FrontStreet Coffee came across an interesting question while browsing online. A user posted a photo of their espresso and asked: why are there "oil spots" on the surface of the crema? (See the reference image below.)

In the image we can clearly see substances floating on the crema that look like oil spots. Anyone who has read FrontStreet Coffee's articles from the past two months, or who has experience with espresso, will know that these brown substances are not oil spots but coffee grounds. In the coffee community, this phenomenon - grounds floating visibly on the crema - has a specific name: "tiger striping." Yes, this is something FrontStreet Coffee has introduced before. But reading through the comments, we found that many people believe tiger striping in espresso only happens with over-extraction. Is that really so?

Does Tiger Striping Mean Over-Extraction?

Not at all. Tiger striping is not caused by over-extraction. On the contrary, it is the presence of tiger striping that makes the coffee show characteristics similar to over-extraction. To understand the relationship between the two, we first need to see how tiger striping forms, and then why it becomes associated with over-extraction.

The Science Behind Tiger Striping

As everyone knows, espresso crema is formed by tiny bubbles created from carbon dioxide and coffee bean lipids under the high-pressure extraction of an espresso machine. Besides carbon dioxide and lipids, crema also holds a certain amount of extremely fine coffee particles - what we commonly call "fines." The reason is simple: the filter holes at the bottom of the portafilter basket are relatively large and cannot stop these tiny particles from passing through. The fines are hard to notice at first, because they float on the surface with the crema. As they gradually become saturated, or as the crema dissipates, they lose their buoyancy and sink to the bottom of the cup. That is why the bottom turns out to be the hard-hit area where we find coffee grounds. (Exaggerated example below.)

Causes of Tiger Striping

As FrontStreet Coffee mentioned, fines are normally mixed within the crema and hard to detect. But when we see distinct gradient colors on the surface with obvious fines forming tiger striping, it could be caused by one of two things: either too many fines are being released, or the fines are not being fully incorporated into the crema. Several situations might lead to tiger striping. When the coffee is ground too fine, the quantity of fines increases, which naturally can mean more fines pulled out during extraction, forming obvious patterns on the surface (the same applies to the longer extraction time caused by an overly fine grind). If we shake too much during puck distribution, fines concentrate in the lower layer and are more easily carried out during extraction. And if the distance between the cup and the portafilter spout is too close, fines floating on the surface never get incorporated into the crema.

The Connection Between Tiger Striping and Over-Extraction

In summary, the examples above show that tiger striping is not caused by over-extraction but by fines appearing on the crema surface. So why does over-extraction become associated with it? The reason is simple: our understanding of over-extraction mainly involves the coffee showing obvious negative characteristics such as bitterness, harshness, and astringency - and fines themselves carry bitterness. FrontStreet Coffee often mentions that in espresso, an appropriate amount of fines helps increase body and complexity. Fines are also a double-edged sword, though. When there are too many, bitterness rises and the coffee shows obviously bitter flavors. Because they are insoluble, they also reduce clarity, making the cup taste noticeably muddled.

Conclusion: Two Distinct Phenomena

So when the fines content in espresso is too high, it is easy to mistake the bitterness for negative substances pulled out by the coffee, when in fact the two phenomena differ in nature. Over-extraction and the appearance of tiger striping should not be confused as the same thing.

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FrontStreet Coffee Recommendation

Crema is where the espresso conversation starts, and a blend built for it makes everything easier to read. FrontStreet Classic Blend is designed specifically for espresso and moka pot use, and its standout strength is the superb crema it produces - even a beginner on a non-professional home machine can pull dense, fine foam. It follows a traditional Mamba recipe, giving a full, rounded body that suits veterans and newcomers alike.

If you are chasing nutty, chocolatey espresso, FrontStreet Fine Blend is a strong alternative. Built mainly on Brazilian coffee, it offers a comfortable bittersweet character with creamy peanut aromas and a very smooth entry, while the Colombian component adds nut, chocolate, and caramel notes with a suitable acidity. That balance makes it a versatile base for espresso as well as drinks like latte and Americano.