Why is Espresso Hard to Dial in on Rainy Days? What Are the Causes of Poor Espresso Extraction from Coffee Machines?

Spring Rainy Days: The Challenge of Perfect Espresso Extraction

As temperatures gradually rise and frequent rainy weather arrives, this signifies that Guangdong has begun to step into the realm of spring. Do you think FrontStreet Coffee is going to celebrate this season of rejuvenation? No! In the current continuous spring rain, for those coffee professionals who work early shifts and adjust coffee early in the morning, this will be a season of drinking espresso until satisfied (including FrontStreet Coffee).

Long-time followers have likely noticed that this is a topic FrontStreet Coffee brings up every spring. As mentioned earlier, compared to sunny days, espresso on rainy days is indeed more challenging to adjust. This isn't just true for baristas—if you frequently visit coffee shops in your daily life, you've probably noticed that espresso drinks on rainy days tend to be less impressive than on sunny days. If you happen to visit early in the morning, you might even witness the spectacular sight of a bar counter filled with espresso shots. This represents one of the major challenges that rainy weather brings to baristas.

Why Espresso Requires Daily Adjustment

The reason espresso needs daily adjustment is not only because the state of coffee beans is constantly changing, but also because environmental factors play a significant role. Humidity, temperature, and atmospheric pressure all affect coffee extraction. Some of these influences act on the coffee itself, while others affect the espresso machine's extraction process.

The primary factor affecting coffee itself is humidity. When there are more active water molecules in the air, environmental humidity increases, creating the possibility of coffee beans being invaded by moisture (becoming damp). In high humidity conditions, ground coffee will have more "stickiness," meaning it will clump together more easily than usual and stick to everything it touches.

Coffee grounds in this state extract very inconsistently. Even when using the same weight for each dose, the presence of clumped grounds causes frequent channeling, potentially resulting in different flow rates, extraction times, and flavors for each shot. For example, one shot might use 20g of coffee to extract 40ml in 30 seconds and taste excellent, while the next shot with the same 20g might extract 40ml in only 25 seconds, resulting in under-extracted espresso.

As FrontStreet Coffee mentioned earlier, some factors affect the espresso machine itself. Because espresso machines use pressure-assisted extraction—that is, they use pressure to aid extraction during brewing. The pressure is generated by the machine's pump, creating a pressure difference relative to atmospheric pressure. However, atmospheric pressure is relatively lower on rainy days, so the reduction in external pressure causes the pump's actual extraction pressure to decrease. This pressure drop means reduced extraction efficiency, combined with humidity effects, making it more challenging to adjust delicious espresso on rainy days.

Quick Espresso Adjustment Tips for Rainy Days

Since these are environmental factors, to quickly adjust espresso properly, we can only reduce the impact of these environmental factors (for example, to reduce moisture's effect on coffee beans, FrontStreet Coffee keeps doors and windows closed throughout the day while running two air conditioners for dehumidification, thus reducing water molecules in the air (if it feels stuffy, we briefly turn on cooling?). Then at closing time, FrontStreet Coffee transfers coffee beans from the hopper back to their bags, using sealing to minimize moisture invasion as much as possible.

Additionally, we can use distribution needles to break up clumped coffee grounds, effectively reducing channeling. However, this method increases preparation time and isn't suitable for coffee shops with high volume.

Adapting to the Challenges

Other influences are basically unadjustable, leaving us only able to adjust espresso flavor based on our understanding of extraction. If you absolutely cannot get the espresso right at the moment, you can wait appropriately for the environmental impact on extraction to decrease before starting again. For coffee shops that need to start serving immediately, you can appropriately relax the standards for good espresso, mainly regarding aroma. Because high humidity environments affect olfactory sensitivity while reducing coffee aroma volatilization, making it harder to detect coffee aromas.

In this situation, what we need to do is ensure the espresso has proper extraction with balanced sweet, sour, and bitter flavors, and performs well when made into Americanos or lattes (since specialty coffee drinks are the main selling products in coffee shops). When humidity decreases, we can readjust the coffee. (This is also one of the reasons why rainy day coffee never tastes as good as sunny day coffee—the aroma is concentrated but not prominent.)

Final Recommendations

Finally, due to the unstable extraction conditions on rainy days, we cannot simply "set it and forget it" after adjusting espresso in the morning. To ensure consistent quality, it's best to recheck the espresso flavor every four hours, ensuring real-time corrections to the coffee taste~

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473