What Are the Requirements for Distributing Espresso Coffee Grounds? What Should Be Noted When Tamping Coffee Pucks? What is the Channeling Effect in Espresso Extraction?

Because pressurized extraction is quite special, to make a delicious espresso, in addition to finding the right conventional extraction parameters such as grind size, time, ratio, and water temperature, we also need to perform some additional preparation steps. These additional preparation steps are essentially about adjusting the distribution of coffee grounds in the portafilter basket before attaching it to the coffee machine.

And "distribution" and "tamping" are the "two-part" preparation movements. Although these two steps may seem very simple, they actually contain many subtle details that can affect extraction and change the taste of coffee. Today, FrontStreet Coffee will share what details we need to pay attention to during the distribution and tamping process, and what distribution and tamping are actually for!

Coffee Distribution

In essence, whether it's distribution or tamping, they share a common primary purpose: to prevent channeling. Water is inherently lazy and flows to places where it can pass easily. When coffee grounds are not evenly distributed in the portafilter basket, gaps between the grounds will form numerous "channels." These channels will cause water to concentrate on extracting specific areas during the extraction process. This leads to hot water being unable to fully extract every coffee particle in the puck, resulting in severely over-extracted coffee in the channels and severely under-extracted coffee outside the channels. The coffee tastes both sour and bitter, making it very difficult to accept.

Therefore, the first thing we need to do is "distribution"! After pouring a measured amount of coffee grounds into the portafilter basket, we need to redistribute them so that the coffee grounds are evenly distributed throughout the entire basket. This way, after the coffee grounds are tamped, there won't be channels for hot water to "take shortcuts." However, most people typically use the portafilter directly to receive coffee grounds from the grinder, which causes all the grounds to pile up in the center, forming a "small hill" or an uneven state with more on one side and less on the other. In these two situations, FrontStreet Coffee does not recommend using a distribution tool directly for distribution.

Because the distribution tool itself forms a downward pressing force when pressed down, this force will first press the grounds piled in the center, and then the distribution tool will distribute and flatten the surface grounds that haven't been compacted.

This situation will result in the coffee puck appearing flat on the surface, but in reality, most of the grounds are piled in the center, with very few grounds around the edges. And a puck in this state has a high probability of producing channeling during extraction! Not just because of more gaps, this is also related to espresso extraction. Let me repeat: water is inherently lazy, so it flows to places where it can pass easily. Even if we distribute the grounds evenly and tamp them properly, water still has easy channels to flow through! That is: "the edge of the puck," the area where coffee grounds meet the portafilter basket.

Although the puck may appear firmly tamped and airtight, in reality, because the surface of the portafilter basket is smooth and flat, it doesn't completely contact the puck. Under the high pressure of 9 bar, water will first flow to these gaps, then penetrate to the center, extracting the coffee grounds in the center. This is why when espresso is being extracted, the coffee liquid converges from the edges to the center.

Alternatively, we can turn off the extraction button as soon as the espresso starts to flow, then knock out the puck and cut it open to observe the dry and wet states. You will find that the top, surrounding edges, and bottom are all moist, but only the coffee grounds in the middle are dry. This is the extraction sequence of espresso: first the periphery, then the interior. This also explains why the extracted espresso has distinct layers - because not all coffee grounds are evenly extracted, and varying amounts of sour, sweet, and bitter substances create these diverse layers.

Therefore, if the coffee grounds form a small hill in the portafilter basket when receiving them, it's best not to use a distribution tool directly. You can first use your fingers to level the coffee grounds from side to side, and then use a distribution tool for distribution. Of course, friends with the means (referring to time) are best to use distribution needles, which not only allow for more even distribution of coffee grounds but also break up clumped coffee grounds. Additionally, we can change the receiving steps to reduce tedious operations during distribution, for example, changing from directly receiving grounds with the portafilter to using a grounds receiver. A grounds receiver allows the grounds to first fall from the side, then the center, greatly reducing tedious distribution operations. However, this is less friendly for stores with high output, so everyone can choose based on their own situation.

Tamping

The purpose of tamping is to strengthen the connection between coffee grounds, preventing high-impact hot water from easily breaking through the coffee grounds and affecting extraction. Compared to distribution, tamping coffee grounds is much simpler. We only need to ensure that the downward pressure applied is even and appropriate! Many people struggle with tamping properly, largely due to incorrect posture (as shown in the picture), such as non-vertical arms or uneven force application. This can be easily improved - just use your purchasing power - or rather, if we practice diligently, we can master the true essence of tamping!

The most common tamping technique is to have the thumb and index finger each hold one side of the tamper, with the remaining three fingers and palm wrapping around the handle, keeping the arm vertical and applying downward pressure.

But as FrontStreet Coffee mentioned, this skill truly requires continuous practice to grasp its essence. So if you don't want to use your purchasing power, continuous practice is the best choice! And when we can properly perform distribution and tamping movements, we can more easily make delicious espresso!

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