Introduction:Do you know why professional coffee shops make adjusting their espresso the very first task of each day? It’s not just a routine — it's essential to ensure that every cup maintains stable and excellent flavor. Factors such as the freshness of the coffee beans, gas release, daily humidity and environmental changes, and even grinder wear can all directly affect the outcome of espresso extraction. This article will take an in-depth look at these key factors, helping you understand the logic behind what baristas adjust every day.

Among a barista’s daily tasks, one of the most challenging is the pre-opening “espresso adjustment.” When it's a rainy or overcast day, this task becomes especially tough — a small misstep could result in over-extracted espresso with a bitter taste that’s truly unpleasant.

Many customers or amateur enthusiasts often wonder: since you only need to control parameters like dose, water temperature, yield, and grind size to remain constant, why can’t you maintain a stable flavor? In theory, this should work, but in practice, even just a few hours apart, the taste of coffee can vary significantly due to various variables. That’s also why every coffee shop still insists on adjusting espresso extraction parameters every day.

The reason espresso extraction demands such precision lies in its high-pressure brewing method (about 9 bar). Under such pressure, soluble substances in the coffee are rapidly released, but the extraction time is extremely short, so control over each parameter must be very precise. High water temperature and fine grind put the coffee at a highly sensitive balance point of extraction; any slight change in bean condition or environment can cause significant fluctuations in flavor.

First, let’s look at the changes in the state of the coffee beans themselves. After roasting, coffee beans continue to release large amounts of carbon dioxide, especially dark roasted beans, which produce even more gas. This carbon dioxide inhibits the release of flavor compounds and affects extraction efficiency. When you use freshly roasted beans to make espresso, although you may see a thick crema, the flavor is often thin and the aroma not pronounced, and the crema can quickly dissipate or become hard and clumpy. This is precisely because the release of carbon dioxide replaces the dissolution of some flavor compounds.

Over time, the carbon dioxide inside the beans gradually escapes, allowing flavor compounds to be released more smoothly during extraction, making the coffee’s aroma and mouthfeel richer and smoother. If you want to achieve a similar extraction effect using freshly roasted beans, you must appropriately adjust grind size, water temperature, or pressure parameters to suit the beans’ current state.

In addition, the release of carbon dioxide also affects the speed of water penetration. When hot water contacts the coffee grounds, the rapid release of carbon dioxide forms bubbles, and the counterforce from these bubbles hinders the downward flow of water, leading to uneven extraction. Therefore, even with the same parameter settings, coffee beans at different times may require different extraction times and pressure adjustments.

Next, we cannot overlook the impact of weather and environment. Many baristas have experienced how much harder it is to adjust espresso on rainy or cloudy days compared to sunny ones. This is because a high-humidity environment causes coffee beans to absorb moisture more easily, and ground coffee is more prone to clumping. If there are many clumps in the coffee puck, water will flow through certain areas, causing what’s known as “channeling,” resulting in uneven extraction, over-extracted bitterness or acidity, and extremely unbalanced flavors.

Furthermore, atmospheric pressure is usually lower on rainy or cloudy days, which affects the extraction pressure of the espresso machine, causing the actual extraction pressure to fail to reach the expected 9 bar, thereby affecting overall extraction performance. Therefore, in poor weather conditions, baristas need to flexibly adjust grind size, tamp pressure, and extraction time to ensure stable coffee performance.

Finally, don’t overlook the issue of grinder burr wear. Even if you use the same grinder, the same setting, and the same coffee beans every day, the actual particle size of the ground coffee may still vary slightly. This is because the burrs of the grinder gradually wear down over long-term use, increasing the distance between them and producing coarser coffee grounds. To maintain stable extraction, baristas may need to constantly fine-tune the grind setting, and sometimes even replace the burrs.

Additionally, if you switch to a different batch or origin of coffee beans, the density, hardness, and moisture content of each batch may vary, meaning the previous grind settings may no longer be appropriate and need recalibration. This is also why professional coffee shops spend time testing and adjusting espresso extraction parameters at the start of each day, ensuring every cup delivers the best possible flavor.

In summary, there are many factors that influence the flavor of espresso extraction, including the freshness of the coffee beans and their carbon dioxide release, environmental humidity and atmospheric pressure, as well as grinder wear and calibration. Only through careful daily observation and adjustment can we ensure the stability and deliciousness of every cup of espresso. For baristas, this is not just a skill — it’s an art.

The above content is compiled by CoffeeHunters, a coffee news website.