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 creep upward and the rainy weather sets in, Guangdong begins to step into spring. You might think FrontStreet Coffee is going to celebrate the season of renewal. Not a chance. In the middle of a stretch of spring rain, for the coffee professionals who work the early shift and dial in coffee first thing in the morning, this is a season of drinking espresso until they are sick of it. FrontStreet Coffee included.

Long-time readers have probably noticed that this is a topic FrontStreet Coffee raises every spring. As we have said before, espresso is genuinely harder to dial in on a rainy day than on a sunny one. That is true not only for baristas: if you visit coffee shops regularly, you have likely noticed that espresso drinks on rainy days are less impressive than on sunny ones. Stop by early enough and you might even catch the sight of a bar counter lined with sacrificed shots, one of the big challenges that wet weather brings to baristas.

Why Espresso Requires Daily Adjustment

Espresso needs daily adjustment not only because the state of the beans keeps changing but also because environmental factors matter a great deal. Humidity, temperature, and atmospheric pressure all affect extraction. Some of these act on the coffee itself, while others act on the machine's extraction process.

The main factor acting on the coffee is humidity. When there are more active water molecules in the air, ambient humidity rises and beans may take on moisture. In high humidity, ground coffee becomes more "sticky," clumping more easily and adhering to whatever it touches.

Grounds in that state extract very inconsistently. Even with the same dose weight each time, the clumps cause frequent channeling, so shots can differ in flow rate, extraction time, and flavor. One shot might run 20g to 40ml in 30 seconds and taste excellent, while the next 20g shot runs 40ml in only 25 seconds and comes out under-extracted.

As FrontStreet Coffee noted, other factors act on the machine itself. Espresso machines extract with the help of pressure, using the pump to create a pressure difference relative to atmospheric pressure. On a rainy day, atmospheric pressure is relatively lower, so the drop in external pressure lowers the pump's actual extraction pressure. That reduced pressure means lower extraction efficiency, and combined with the humidity, it makes dialing in good espresso on rainy days a real challenge.

Quick Espresso Adjustment Tips for Rainy Days

Since these are environmental factors, the best we can do to dial in quickly is to reduce their impact. To limit moisture reaching the beans, FrontStreet Coffee keeps doors and windows closed all day and runs two air conditioners for dehumidification, cutting the water molecules in the air (if it gets stuffy, we briefly switch on cooling). At closing time, we transfer the beans from the hopper back into their bags, sealing them to keep moisture out as much as possible.

We can also use distribution needles to break up clumped grounds, which effectively reduces channeling. That said, the method adds prep time and is not suited to high-volume shops.

Adapting to the Challenges

Other influences are basically beyond our control, which leaves us adjusting the flavor based on our understanding of extraction. If you simply cannot get the espresso right in the moment, you can wait a while for the environmental impact to ease before trying again. For shops that need to start serving immediately, you can loosen the standard for good espresso, mainly where aroma is concerned, because high humidity dulls the sense of smell while also reducing how much aroma the coffee releases, making it harder to detect.

What matters most is to ensure the espresso has proper extraction with balanced sweet, sour, and bitter notes, and that it performs well as an Americano or a latte, since specialty drinks are the bread and butter of a coffee shop. When humidity drops, you can readjust. This is also one reason rainy-day coffee never tastes as good as sunny-day coffee: the aroma is concentrated but not prominent.

Final Recommendations

Finally, because extraction conditions are unstable on rainy days, we cannot simply set the espresso and forget it after the morning adjustment. To keep quality consistent, it is best to recheck the flavor every four hours and correct the taste in real time.

FrontStreet Coffee Recommendation

When the weather is working against you, a forgiving blend helps. FrontStreet's everyday pick is the FrontStreet Classic Blend, designed for espresso and the moka pot, with outstanding crema that even a beginner on a home machine can pull, and a full, gentle body from a traditional mamba recipe. It will hold up on a muggy morning.

For traditional Italian flavor, the FrontStreet Specialty Blend and FrontStreet Coffee's Commercial Blend both add a touch of Robusta to an old-school recipe, giving butter, nut, spice, dark chocolate, and toast aromas with a thick body and plenty of golden crema. And if you prefer nutty, chocolate-forward espresso, the FrontStreet Black Cocoa Blend uses a large share of Brazilian beans for a comfortable bitter-sweetness, a creamy peanut aroma, and balanced flavor, with the pricing to make it a shop-friendly daily driver.