What to Do with Clumped Coffee Powder: The Impact of Humidity on Coffee Extraction and How to Adjust Grind Settings on Rainy Days

With the continuous drizzle of recent days, Guangzhou has officially welcomed spring. Recently, some friends have privately asked, "How should espresso be adjusted during rainy days?" So this installment of our barista training series will explain how FrontStreet Coffee handles this situation, hoping to help everyone.

What Effects Do Rainy Days Have?

Some who may not fully understand might think that sunny and rainy days are very normal occurrences, so why specifically discuss adjusting espresso during rainy days? For baristas who have been deeply affected, they have a profound understanding. The direct impact of rainy days is the increased humidity in the air. FrontStreet Coffee measured the indoor relative humidity today at 78%, which is considered a high humidity level.

Humidity

Humidity mainly affects espresso extraction in two aspects. The first is coffee beans/ground coffee. We know that coffee beans should be stored in a cool, dry environment. In indoor environments with such high humidity, coffee beans can easily become damp. Therefore, FrontStreet Coffee suggests that especially during closing time at night, the coffee beans from the bean hopper should be returned to the coffee bag and sealed for storage.

Sometimes when we are preparing drinks, we grind coffee beans. After each grinding, coffee grounds will remain in the grinder's hopper or in the channel from the burrs to the dispensing port. These ground coffee particles are extremely susceptible to moisture interference, with common phenomena including clumping and flavor loss. If you don't clean these grounds thoroughly, they will become the coffee grounds used for the next espresso. This is also a main reason why after we adjust our espresso coffee, subsequent extractions may become unstable.

The second point is that generally, the higher the humidity, the lower the atmospheric pressure. The pressurization of an espresso machine to 9 bar is calibrated under normal atmospheric pressure. If normal atmospheric pressure is less than 1, then the fixed pressurization of the coffee machine will also be less than 9 bar. This is also why espresso output becomes unstable when weather changes suddenly.

How Should FrontStreet Coffee Adjust Espresso Output?

First, ensure that coffee beans are not exposed to excessively humid environments. FrontStreet Coffee's approach is to return the coffee beans from the bean hopper to the coffee bag during closing time at night, and clean the oils and moisture from the bean hopper. We regularly empty the remaining grounds from the bean hopper to avoid affecting the next espresso.

When adjusting the espresso machine every morning, we first check if the grinder has been thoroughly cleaned, then add the coffee beans. We use yesterday's grind setting and extraction parameters for extraction. Yesterday's grind setting was 2, with extraction parameters of 18.5 grams to extract 35 grams of coffee liquid, taking 28 seconds. Today's test showed the actual extraction time was 22 seconds, with significantly faster flow rate.

Note: Due to high humidity, coffee grounds tend to clump, so distribution becomes particularly important. Uneven distribution can easily lead to channeling or excessive local density, resulting in too slow flow rates.

Then we adjusted the grind setting for a second extraction. For espresso grinding, if extraction results are similar, it's recommended to make small adjustments, one notch at a time. This time we adjusted one notch finer to setting 1.9 (when making it finer, we move the dial while the machine is running to avoid grinder jamming). After extraction, the time was 25 seconds. When tasting the espresso, it felt slightly thin and the flavor wasn't complete.

Then we continued to adjust one notch finer (setting 1.8) for testing, with a time of 27 seconds. The taste was quite good. So we tested the stability of this parameter a second time and found that the flow rate in the latter part of the second extraction was too fast, with a time of 25 seconds. Observing the coffee puck, we determined that the finer grinding caused the puck volume to decrease, resulting in tumbling on the puck surface. Therefore, we chose to increase the dose to 19 grams. After multiple confirmations of extraction, we established today's extraction plan: setting 1.8, 19 grams of coffee grounds to extract 35 grams of coffee liquid, with a time of 28 seconds.

Even after adjusting the espresso in the morning, it doesn't mean it will be suitable for the entire day. The grind setting should be adjusted appropriately based on actual conditions to ensure stable output throughout the day.

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473