What is a tiger stripe concentrate? Where does the fat in espresso come from? How does fine powder affect coffee?

Today, when I was surfing the Internet in Qianjie, I found an interesting question card. A netizen put a photo of its extracted espresso on it and asked: why is there an "oil idea" on the oil surface of espresso? (the picture is referenced below)

From the picture above, we can see that there is indeed a substance similar to the "oil spot" floating on the surface of the grease. However, I believe that after reading the street article two months ago or experienced friends, it is clear that these brown substances are not so-called "oil ideas", but coffee powder. In the circle, the phenomenon that this coffee powder floats on the grease surface can be clearly seen has a special name-"tiger spot". Yes, it was introduced and shared on the front street before. But as Qianjie flipped through the comment area and found that many friends think that the "tiger stripes" of this espresso is an outstanding phenomenon, is this really the case?

Is there any "tiger spot" in espresso? No, no, no. On the contrary, it is the appearance of "tiger stripes" that leads to the performance of coffee that is similar to that of over-extraction. So in order to help you understand the relationship between the two, we need to first understand how tiger markings are produced, and then why it has something to do with over-extraction!

It is well known that the oil of espresso is a small group of bubbles produced by carbon dioxide and lipids of coffee beans under high pressure extraction. In addition to carbon dioxide, coffee bean lipids, the oil will also contain a certain amount of very fine coffee powder, that is, we often talk about fine powder. The reason is very simple, because the filter hole at the bottom of the powder bowl will be relatively large, it can not prevent the small coffee powder from passing through. These fine powders will be difficult to detect at first, because they will float on the coffee liquid with the oil, but as they become saturated, or the oil will dissipate, the fine powder will fall to the bottom of the coffee because it loses buoyancy, so the bottom of the coffee has become the "worst-hit area" where we found the coffee powder. (exaggerated ↓)

But as Qianjie said, under normal circumstances, fine powder is mixed in grease and is difficult to be detected. But if we see distinct gradients on the surface of the grease, there are obvious fine powders on the surface to form "tiger markings". That may be caused by two situations: either because the fine powder releases too much, or because the fine powder is not completely washed into the grease! Qianjie simply lists here the situation that may lead to tiger markings: when the coffee powder is ground too fine, the number of fine powder will be increased, which may naturally cause more fine powder to be extracted during extraction. Obvious lines are formed on the surface (in the same way that the extraction time caused by grinding is increased) Or we shake the powder too much, so that the fine powder is concentrated to the lower layer, so that the fine powder can be brought out more easily during extraction, and the distance between the concentrating cup and the outlet is too close. as a result, the fine powder floating on the surface can not be washed into the grease, and so on.

In short, we can learn from the above cases that the appearance of tiger markings is not caused by overextraction, but because the fine powder appears on the surface of the oil. Then why is this situation related to tiger markings? The reason is very simple, our understanding of the over-extract is that the coffee has obvious bitter, miscellaneous, astringent and other negative performance, while the fine powder itself has a bitter taste! Qianjie often says that in espresso, the presence of the right amount of fine powder helps to increase the alcohol thickness and layering of the coffee. But at the same time, fine powder is also a double-edged sword, when there is too much fine powder, the bitterness will be increased, thus making the coffee appear obvious bitterness. At the same time, because of its insoluble properties, it will also lead to a decline in the cleanliness of coffee, making it drink with obvious miscellaneous feeling.

Therefore, when the fine powder contains too much in the concentrate, it is easy to cause people to mistakenly think that some negative substances have been extracted from the coffee because of the bitter taste, but in fact there is still a certain difference in the nature of the two. Therefore, the emergence of super-excellence and tiger stripes can not be confused.

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