What Causes Clumped Espresso Crema? Why Doesn't Espresso Coffee Puck Form Properly?

Common Issues in Espresso Extraction: A Comprehensive Collection 2.0

Hello everyone, today FrontStreet Coffee is sharing a comprehensive collection of very common issues that arise during the espresso extraction process—version 2.0.

It has been over half a year since we shared "Common Issues in Espresso Extraction 1.0." As for why it took so long to share the second installment, there must be a reason—it's definitely not because FrontStreet Coffee forgot . The issues collected this time are also topics that FrontStreet Coffee has shared in separate articles, so here FrontStreet Coffee will just provide brief answers, and attach corresponding article links to the titles. Friends troubled by these issues can click on the links for more details. Now, without further ado, let's begin today's sharing!

Common Issue 6: Why does the portafilter accumulate water after extraction? Why is the coffee puck wet and loose?

After we extract espresso, the coffee puck we see when removing the portafilter is usually relatively dry without much moisture. However, occasionally, we might find a significant amount of water accumulated in the removed portafilter basket, with the puck being wet, loose, and not holding its shape.

This situation is primarily caused by using too little coffee! When we use significantly less coffee than the recommended amount for the portafilter basket, there will be a wider gap between the coffee puck and the shower head, requiring more hot water to fill before extraction begins. This leads to the inability of the pressure release suction to expel all the hot water from the basket when extraction ends, resulting in water accumulation in the portafilter and a loose, shapeless puck when knocked out. Another situation that can easily cause this is when the coffee grind is too fine. When the coffee is ground too finely, due to the higher resistance of the puck, water passes through the coffee layer more slowly. At the end of extraction, some water may not have passed through the coffee layer in time and was expelled by pressure release, resulting in higher moisture content and a wet, muddy consistency.

Common Issue 7: Why is the post-extraction coffee puck incomplete and not holding its shape?

Many friends are curious about how to judge extraction conditions from the state of the coffee puck. FrontStreet Coffee has actually shared this in this article before. The specific method is very simple—we just need to observe whether the knocked-out puck is complete and holding its shape after extraction.

If the puck surface shows many small holes, the knocked-out puck is very loose and not holding its shape, or there are significant color differences in the coffee grounds at different positions, then undoubtedly, the extraction was not uniform! Why? Because these are all phenomena that occur after channeling happens during extraction. ("What is channeling?")

The small holes are actually channels, formed because hot water concentrated in these areas to seep out; while the shapeless puck is because the hot water during extraction did not penetrate evenly, and some coffee grounds inside were not fully soaked by hot water. They (each cup of hot water moistened coffee grounds) couldn't connect with other coffee grounds, so the puck cracked when knocked out; the same applies to color differences. Although coffee extraction is never completely uniform, and there will be some color differences in coffee grounds at different positions, they won't be too significant. Uneven extraction will amplify these color differences, creating greater color variation between coffee grounds.

Common Issue 8: Why does espresso crema clump together?

Many friends often encounter the problem of clumping crema! That is, although the extracted espresso has very rich crema, it starts to clump and harden after a short while, with very low fluidity, greatly affecting latte art creation. The main reason for this situation comes from using coffee beans that are too fresh.

As we all know, overly fresh coffee beans contain very rich carbon dioxide, which gives the extracted espresso rich crema. Although this crema is rich, it's very coarse! Because crema is composed of countless small bubbles filled with carbon dioxide, and besides carbon dioxide, these bubbles also contain lipids from coffee beans. Since the amount of coffee lipids is fixed, when there's more carbon dioxide, although more bubbles are filled, the lipids wrapping each bubble will be less. This makes the bubbles break very quickly, and then the crema will harden due to most of the bubbles breaking—this is what we call clumping, which then affects our latte art creation.

The solution is very simple—we just need to let it sit for a period of time, allowing some carbon dioxide to escape before extraction. The resulting crema will be the type that's fine and not prone to clumping! At the same time, the coffee's flavor will become richer due to the reduction of carbon dioxide, which is truly a win-win situation~

Common Issue 9: Does "tiger striping" in espresso indicate over-extraction?

Sometimes, the crema of our extracted espresso may have obvious black stripes, like tiger stripes. Many people consider this "skin" a sign of over-extraction because it's often a characteristic that appears during long extraction times.

In fact, "tiger striping" is not a characteristic that only appears with over-extraction, because it's not burnt coffee oils but coffee grounds that were originally in the portafilter basket. The portafilter basket of an espresso machine is actually also a filtration tool, just not as powerful as filter paper, so some substances besides coffee can pass through the filter holes of the basket and be "pressed out" by the coffee machine, such as coffee oils and coffee grounds! The black stripes on the crema surface are coffee grounds that were pressed out from the basket and then floated on the crema surface because they are smaller particles and lighter in weight.

Generally, the espresso we extract won't have very obvious stripes, meaning there won't be many fine coffee grounds. The main reasons for tiger striping are twofold: one is grinding too fine! When coffee is ground too finely, there will be more fine particles, and this also increases puck resistance and extends extraction time, making it easier for many fine particles to be pressed out of the basket; another situation is because we shook too much during distribution, causing extremely fine particles to settle at the bottom of the basket, making them easily pressed out during extraction. The presence of fine particles has both advantages and disadvantages. The advantage is that they can give coffee higher body and richer flavor; the disadvantage is that they increase the concentration of bitterness. When there are too many fine particles, the bitterness becomes more obvious, making it taste as if it were over-extracted.

So above are all the common issues of espresso extraction this time. If you have any other questions, feel free to leave them in the comments section, and FrontStreet Coffee will share them in a special topic next time~

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