Can't Extract to Target Liquid Weight? Should You Press the Extraction Button Again? Is Double-Extracted Espresso Good to Drink?

Understanding Espresso Extraction Interruptions

When extracting espresso, we typically use a continuous method to extract the target liquid volume in one smooth process. However, sometimes due to momentary carelessness or accidental touches, we might prematurely stop the espresso extraction.

While this might be considered a Ristretto, as FrontStreet Coffee mentioned, except for Flat Whites, other espresso-based drinks don't use Ristretto as their base. Therefore, when this situation occurs, if we want to get a properly flavored latte or Americano, we have to obediently extract another shot of espresso. However, some more adventurous friends might start thinking: since it wasn't extracted enough, can we press the extraction button again and perform a "segmented extraction" like pour-over coffee?

Experiment: Can Espresso Be Extracted in Multiple Stages?

Very good, since you're all so curious, FrontStreet Coffee will test this for everyone! In this experiment, FrontStreet Coffee will extract three shots of espresso: one normal extraction and two segmented extractions. The two segmented espresso shots will have different interruption points to see what different flavors emerge from coffee interrupted at different stages, and whether espresso extraction can truly be divided into two parts!

Experiment Setup and Results

The coffee beans used in this experiment are still the Warm Sun Blend, after all, FrontStreet Coffee only has one espresso grinder~ Then ground to Galileo Q18's 1.2 setting, with a coffee-to-liquid ratio of 1:2, meaning 20g of coffee grounds to extract 40ml of espresso. First, extract a regular shot! Since it was extracted all at once, the extraction time was a standard 30 seconds. The flavor profile remains Warm Sun's classic whiskey aroma, butter cookies, and subtle berry acidity.

Two-Stage Extraction Experiment

Next is a two-stage extracted espresso! We stopped the extraction when it reached half the target liquid volume. At this point, the extraction time was 20 seconds, then we restarted extraction after a two-second interval. The result: the remaining 20ml was extracted in just 4 seconds, with very pale coffee liquid, and total extraction time of 24 seconds. The flavor profile of this espresso was quite thin, with flavors present but not distinct.

Late-Stage Interruption Experiment

Finally, an espresso interrupted near the end phase! FrontStreet Coffee stopped extraction when it reached two-thirds completion. At this point, the parameters were 25 seconds, 31ml! Then after a two-second interval, extraction was restarted! Similarly, the remaining 10ml was extracted in just 2 seconds. This espresso was less thin compared to the second cup, with more body and fuller flavor. However, this can only be compared to the second cup's severely under-extracted coffee. Compared to the first cup, its performance was still relatively weak.

The Science Behind Failed Extractions

So we can understand that if we accidentally stop extraction during espresso preparation, even if we restart it, it's difficult to fully extract the remaining substances from the coffee! The reason for this situation comes from the unique extraction method of espresso machines - pressurized extraction!

Pressurized extraction means when we start the extraction button to make espresso, the espresso machine begins operating, providing 9 bar pressure to forcefully extract substances from the coffee using hot water. This pressure pushes the coffee puck downward, compacting it, thereby increasing resistance and allowing more even distribution of hot water! At the same time, when hot water contacts the coffee puck, large amounts of carbon dioxide rush out. They compress the space,同样 adding obstacles to the flow of hot water. Thus, in such a space, hot water can only "humbly" slowly permeate downward.

But if we stop extraction midway, the originally saturated spatial structure is broken. The back-suction force from the brew head will suck away all substances from the surface of the coffee puck. Meanwhile, after extraction, the density of the coffee puck has changed. Thus, the factors that originally hindered hot water flow disappear completely. When restarted, the released hot water can directly seep quickly through the opened channels in the coffee bed. The too-fast flow rate inevitably prevents hot water from fully extracting coffee substances, which is why the large amount of coffee liquid released in those few seconds appears so pale.

Conclusion: Why Restarting Isn't Recommended

Such coffee liquid not only produces more bitter flavors due to channeling effects but also dilutes the originally well-extracted espresso due to its low concentration. Therefore, when we accidentally close extraction during espresso preparation, it's best to extract a new shot of espresso rather than performing a second extraction on the same coffee puck. This avoids having the final cup of espresso, full of unstable factors, completely destroy the wonderful coffee experience.

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