What Hinders Coffee Extraction? Coffee Extraction Principles and Applications

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The most frustrating part of making coffee is probably figuring out how to achieve better extraction. Whether it's espresso or pour-over, the primary concern for baristas and coffee enthusiasts alike is extraction. So what factors might prevent us from extracting a good cup of coffee?

Espresso Extraction

Regarding espresso extraction, FrontStreet Coffee has previously discussed various aspects, such as whether the ground coffee has clumps, paying attention to filling gaps when distributing coffee, applying even pressure when tamping, and how to make adjustments. However, when it comes to pressure extraction, sometimes it's still unstable, leading to inconsistent coffee quality. Why is this?

1. Are you paying attention to your coffee machine?

If you're using a high-end espresso machine, many problems won't arise. However, many standard commercial models actually depend on luck for their performance. After all, even if the coffee machine components are imported, if the domestic assembly technology is poor, you probably won't be able to produce quality espresso. I once used a commercial espresso machine where the distribution copper block inside the brew head wasn't properly installed, resulting in water "leaking sideways." I had to compensate by adding more coffee to the side with stronger water flow each time I filled the portafilter to balance the extraction. Of course, this was only a temporary fix, and it was precisely the coffee machine issue that prevented us from extracting proper espresso.

2. Your tamper

The tamper is your weapon for compressing coffee grounds, whether it's a calibrated tamper or a traditional one. However, tampers aren't necessarily ready to use right out of the box, even the ones that come with the coffee machine. Take a look at the image below:

Using too much coffee and seeing indentations is one issue, but more importantly, this tamper doesn't match the portafilter basket—as you can tell from the layer of coffee grounds around the outer edge. Although most portafilter baskets on the market have a diameter of 58mm, slight variations in basket diameter, or not purchasing a tamper that best fits your basket's diameter, can result in some coffee grounds not being properly compressed. This makes it easy to over-extract during brewing.

3. Pressure

The pressure displayed on most coffee machines (9 bar) is actually the boiler pressure, not the pressure applied to the coffee puck during extraction (some high-end coffee machines have this capability). Due to manufacturing issues, some coffee machines might initially "spray water" (excessive pressure), then suddenly show weak water flow after a few seconds. Such machines naturally hinder our normal extraction process. If you often notice that your espresso starts with a normal flow rate, but then the coffee suddenly becomes pale or the liquid column becomes unstable—after ruling out technique issues—the problem might be with your coffee machine's water pressure output.

Pour-over Extraction

I believe that even and complete extraction is the most important aspect of pour-over brewing. This is a "framework" I learned from making espresso, and understanding this framework helps me better comprehend what factors might hinder our pour-over extraction.

1. How well is your coffee ground?

Although we have reference points (like granulated sugar) and data (calibration sieves), I think the most important indicators of a grinder's quality are the uniformity of the grounds it produces and the percentage of fine particles. Because many friends (including myself) use Chinese-made "ghost tooth" grinders, and again due to manufacturing issues (it seems our technology really isn't great), the grind settings provided by coffee bean suppliers don't work well with our machines. Even when adjusting according to our own grinder, we might still encounter problems like flow rates that are too fast or too slow, or fine particles blocking water flow. If the flow is too slow, although we can improve it by adjusting to a coarser grind, the fine particles haven't been reduced, and the uniformity gap becomes larger, causing even more inconsistent extraction states for the coffee grounds during brewing. The resulting coffee certainly won't taste good.

2. Filter paper

The material of the filter paper is one issue, and another is whether to rinse it. In the past, raw wood pulp filter papers had a woody taste, while white filter papers added brighteners or even fluorescent agents to make the product look more appealing, so rinsing filter paper became customary (I'm from Guangdong, so I have a ceremonial feeling of washing everything). However, do high-quality pure white filter papers still require this rinsing step today? My personal opinion is: if you want to rinse them, just moisten them slightly rather than flushing with large amounts of water. The reason is that filter paper is made of wood fibers, and excessive rinsing will alter its permeability, as mentioned in previous articles. Additionally, if the filter paper absorbs water, the coffee grounds will immediately absorb the moisture from the paper upon contact, meaning extraction begins prematurely, leading to uneven extraction states. So if you're concerned about filter paper being "unclean," rather than rinsing repeatedly, why not switch to a different brand!

3. Time/coffee-to-water ratio

Time and coffee-to-water ratio are of course very important in pour-over coffee. Precisely because they're important, I've found that many friends become overly focused on changes in numbers while ignoring the extraction itself—these data points are hindering our extraction. Let me ask you: when making pour-over coffee, do you focus more on the state of water flowing through the coffee bed, or do you stare at time and weight changes? Time and water amount certainly require practice and familiarization for beginners, but I think if you're always thinking "at this time, the water amount should be this much," you're being too obsessive, which might affect the stability of your water flow. For example, you're just pouring water around the outer edge when you suddenly realize you've reached the target ratio and need to return to the center for the final pouring motion. Moving suddenly from the outer edge to the center creates a disruption that leads to uneven extraction.

Mindset in Coffee Extraction

Finally, let me talk about a factor that hinders extraction in both espresso and pour-over—mindset, or way of thinking. People often assume something "is just that way" and then take corresponding actions. For example, if espresso is bitter, just adjust to a coarser grind; if pour-over is sour, just lower the water temperature slightly. This isn't wrong, of course, but we need to understand that extraction is a process where "moving one part affects the whole"—changing one variable causes changes in others. In other words, if you only adjust one parameter while keeping others fixed, it's clearly impossible. When extracting coffee, especially pour-over, we advocate focusing on the coffee itself so that we can make adjustments at any time to achieve better extraction, not just to get coffee with "correct" numbers.

Focus on the coffee itself, approach the various variables in extraction with an open mind, and make dynamic adjustments. All changes are meant to maintain consistent quality output. Then, any factors that hinder extraction will become stepping stones for our improvement~

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