Why Do Coffee Shops Adjust Espresso? Is More or Less Crema Better? Why Is Espresso Harder to Adjust on Rainy Days?

The Challenge of Daily Espresso Calibration

Frankly speaking, FrontStreet Coffee believes that among the daily tasks of a barista, nothing is more painful than the morning routine—calibrating espresso. If there's anything more painful than that, it must be calibrating espresso on rainy days. Because without careful attention, you'll end up with over-extracted shots, drinking until you're afraid.

Some friends find this quite confusing, believing there's absolutely no need for such practice. They think that as long as espresso extraction maintains consistent parameters like pour-over—same dose, water temperature, liquid weight, and grind size—today's coffee shouldn't differ significantly from yesterday's.

Indeed, that sounds correct in theory. However, the probability of getting similar results to the previous day isn't high. Espresso extraction is influenced by numerous factors. Beyond just a day apart, even a few hours difference can result in taste variations using the same parameters. Otherwise, why would espresso calibration still exist in every coffee shop today?

Why Espresso Extraction Requires Such Precision

The strict requirements for espresso extraction primarily stem from its distinctive extraction method—pressurized extraction. Under pressures as high as 9 bar, substances in coffee are extracted rapidly. However, due to the short extraction time, each parameter becomes extremely critical. Water temperature is high, grind is fine... This means that when coffee beans or the surrounding environment undergo slight changes, the coffee's taste is immediately affected.

Changes in Bean Condition

After roasting is complete, coffee beans continuously change their state. This change mainly originates from the degassing of coffee beans. As we all know, coffee beans generate significant amounts of carbon dioxide during the roasting process. The darker the roast, the more carbon dioxide produced. These carbon dioxide gases continuously release outward after roasting completion, and our extraction is affected by this carbon dioxide. Because of these carbon dioxide gases, the dissolution and release of flavor compounds in coffee are inhibited to some extent.

With identical extraction parameters, the higher the carbon dioxide content in coffee beans, the fewer coffee compounds will be extracted, as carbon dioxide hinders water from dissolving flavor compounds. If you've used freshly roasted coffee beans for espresso extraction, FrontStreet Coffee believes you've likely encountered this situation:

When we use freshly roasted coffee beans to make espresso, although the resulting espresso has very rich crema, the coffee's flavor expression is typically weak, thin, with insufficient aroma. The rich crema also dissipates quickly, clumping and hardening. This situation occurs because carbon dioxide emission replaces the release of flavor compounds, thereby affecting the coffee's taste.

But when the beans rest for a period, the extracted coffee not only has very rich aroma but also smooth and delicate crema. If we want to extract similar deliciousness from fresh beans, we need to achieve this by adjusting parameters.

Additionally, the amount of carbon dioxide affects another factor—flow rate. From the moment coffee powder encounters water during extraction, carbon dioxide is instantly released. When released, they form bubbles, and the kinetic energy of these bubbles moving upward creates a reaction force that hinders the downward infiltration of hot water. The same amount of water will require more time to permeate through the coffee powder layer.

Since coffee bean degassing occurs continuously, we need to constantly adjust extraction parameters based on the current state of the coffee beans. Only in this way can we ensure that the coffee extracted each day maintains the same delicious quality. And this is the most important factor in daily espresso calibration. (Additionally, this is because different batches of coffee beans are being used.)

Weather and Environmental Changes

Weather also affects espresso extraction, which FrontStreet Coffee often shares. Espresso on rainy days is always more challenging to calibrate than on sunny days because rain increases environmental humidity, filling the air with active water molecules. Not only do coffee beans absorb moisture more easily, but ground coffee powder also tends to clump more readily. If there are numerous clumps in the coffee powder during tamping, channeling is very likely to occur during extraction. The channeling effect causes water to concentrate in certain areas, leading to uneven extraction, making the coffee both bitter and sour with conflicting and abrupt flavors.

Furthermore, decreased atmospheric pressure also affects the coffee machine's pressure, preventing it from using full force for espresso extraction. Therefore, espresso on rainy days is always harder to extract deliciously because various parameters don't meet optimal standards. For this very reason, we need to adjust these parameters even more, allowing rainy-day espresso to possess the same deliciousness as sunny-day espresso.

Changes in Grind Size

Finally, there are changes in grind size! Although using the same grinder with the same setting to grind the same coffee beans, the particle size ground each day will have certain differences.

The main reason for these differences comes from burr wear. It's not difficult to notice that the grinder's settings continuously decrease. The fundamental reason is that after multiple uses, the grinder's burrs continuously wear down, increasing the distance between them. Consequently, we naturally need to continuously decrease the setting to reduce this gap. (Although this influencing factor is relatively minor.) Additionally, when we switch to different batches of coffee beans, the grind setting also needs to change according to the bean replacement. Because not every roast can produce completely identical coffee beans, the grind setting naturally needs corresponding adjustments.

Therefore, combining these three points, to ensure customers can consistently drink the same delicious coffee, espresso calibration has become the essential daily morning task for coffee shops. In fact, it's not just once in the morning—espresso needs to be calibrated almost every few hours because the impact of bean condition and environmental changes is truly significant.

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Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473