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

The Daily Challenge of Espresso Calibration

Frankly, FrontStreet Coffee believes that among a barista's daily tasks, nothing is more painful than the morning routine of calibrating espresso. And if anything is more painful, it must be calibrating espresso on a rainy day, because without careful attention you end up with over-extracted shots and drink until you're sick of them.

Some friends find this puzzling, convinced there is no need for the practice. They figure that as long as espresso extraction keeps consistent parameters like pour-over does, with the same dose, water temperature, liquid weight, and grind size, today's coffee shouldn't differ much from yesterday's.

That sounds right in theory. In practice, though, the odds of getting a cup close to yesterday's are not high. Espresso extraction is influenced by numerous factors. Even a few hours apart, not just a day, can bring taste variations from identical parameters. Otherwise, why would espresso calibration still exist in every coffee shop today?

Why Espresso Extraction Demands Such Precision

The strict demands of espresso extraction come mainly from its distinctive method: pressurized extraction. Under pressures as high as 9 bar, substances in the coffee are extracted rapidly. Because the extraction time is short, every parameter becomes extremely critical. Water temperature is high, the grind is fine, and so on. That means that when the coffee beans or the surrounding environment change even slightly, the taste is immediately affected.

Changes in Bean Condition

Once roasting is finished, coffee beans keep changing state. This change comes mainly from degassing. As everyone knows, coffee beans generate significant amounts of carbon dioxide during roasting, and the darker the roast, the more carbon dioxide is produced. These gases keep releasing outward after roasting, and our extraction is affected by them. Because of this carbon dioxide, the dissolution and release of flavor compounds in the coffee are inhibited to some extent.

With identical extraction parameters, the more carbon dioxide the beans hold, the fewer coffee compounds are extracted, because carbon dioxide hinders water from dissolving flavor compounds. If you have pulled espresso with freshly roasted beans, FrontStreet Coffee believes you have likely run into this:

When we use freshly roasted beans to make espresso, the shot has very rich crema, but the flavor is typically weak and thin with insufficient aroma. The rich crema also dissipates quickly, clumping and hardening. This happens because the release of carbon dioxide replaces the release of flavor compounds, which affects the taste.

Once the beans rest for a period, though, the extracted coffee has not only a very rich aroma but also smooth, delicate crema. To get similar deliciousness out of fresh beans, we need to adjust parameters to achieve it.

The amount of carbon dioxide also affects another factor: flow rate. The moment coffee powder meets water during extraction, carbon dioxide is released instantly. As it escapes it forms bubbles, and the kinetic energy of these bubbles moving upward creates a reaction force that hinders the hot water's downward infiltration. The same amount of water then takes longer to permeate the coffee bed.

Since degassing is continuous, we need to keep adjusting extraction parameters to match the current state of the beans. Only that way can we ensure the coffee pulled each day keeps the same delicious quality, and that is the most important factor in daily espresso calibration. It also matters because different batches of beans are in use.

Weather and Environmental Changes

Weather affects espresso extraction too, as FrontStreet Coffee often shares. Espresso on rainy days is always harder to calibrate than on sunny days, because rain raises environmental humidity and fills the air with active water molecules. Not only do the beans absorb moisture more easily, the ground coffee also tends to clump more readily. If there are many clumps in the coffee powder during tamping, channeling is very likely during extraction. Channeling causes water to concentrate in certain areas, leading to uneven extraction and a cup that is both bitter and sour, with conflicting and abrupt flavors.

On top of that, lower atmospheric pressure affects the machine's pressure, keeping it from extracting at full force. Espresso on rainy days is therefore always harder to pull well, because the various parameters don't meet optimal standards. For this very reason we need to adjust them even more, so rainy-day espresso can match the deliciousness of a sunny-day shot.

Changes in Grind Size

Finally, there are changes in grind size. Even using the same grinder at the same setting on the same beans, the particle size produced each day differs somewhat.

The main reason is burr wear. You may have noticed that grinder settings keep drifting lower. The root cause is that after many uses the burrs wear down, increasing the distance between them, so we naturally need to lower the setting to close that gap. This factor is relatively minor, though. When we switch to a different batch of beans, the grind setting also has to change with the bean replacement, because not every roast produces completely identical beans, so the grind setting needs corresponding adjustment.

Put those three points together, and espresso calibration becomes the essential morning task for coffee shops aiming to serve a consistently delicious cup. In fact, it isn't just once in the morning: espresso needs calibrating almost every few hours, because the effects of bean condition and environmental change are truly significant.

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FrontStreet Coffee Recommendation

Beans that hold up well under pressure make calibration far easier, and FrontStreet Coffee's PWN Golden Mandheling is a fine choice. Grown in the Gayo Mountain region of Sumatra, the beans are even and full with a low defect rate, and after medium-dark roasting they give a clean, full-bodied black coffee with almost no herbal note, plus chocolate, caramel, and spice flavors.

For a balanced, everyday option, FrontStreet Coffee's Brazil Queen Estate coffee has low acidity with a very balanced body, rich nut and cocoa aromas, and obvious caramel sweetness, going down smooth and gentle. It works well for pour-over, espresso, and the moka pot alike, with excellent crema and strong value.