Introduction to the 3 Extraction Stages of Espresso - What Does Espresso Taste Like?

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In the past, FrontStreet Coffee focused heavily on explaining the preparation steps before locking the portafilter into the group head when sharing knowledge about making espresso, such as dosing and tamping—operations that are highly practical and have significant impact on coffee.

After locking the portafilter into the group head and pressing the brew button, the rest is left to the machine. However, we must also understand how coffee is extracted after pressing this button in order to adjust parameters for better results.

Phase 1: Pre-infusion

Pre-infusion is similar to the bloom stage in pour-over coffee—first releasing a small amount of hot water to moisten the coffee grounds and release carbon dioxide gas. In some older models of coffee machines, there may be no pre-infusion function, making the resting period for espresso beans particularly critical. If the resting time is too short, the coffee beans still contain large amounts of carbon dioxide, which can result in thin-flavored espresso with coarse crema.

Modern coffee machines almost all have this function. Generally, the operation process involves locking the coffee portafilter into the group head, then performing low-pressure water delivery for approximately 2-3 seconds before stopping. After the coffee grounds absorb water, they expand and release gas, thereby improving subsequent extraction efficiency and stability.

During pre-infusion water delivery, no pressure increase is needed because if normal 9-bar pressure is used for pre-infusion, it's very likely to break through the surface layer of coffee, causing channeling effects.

Another important aspect of pre-infusion is timing. The set pre-infusion time is related to the freshness of the coffee beans. If the coffee beans are too fresh, they require longer pre-infusion time to release carbon dioxide. Generally, pre-infusion time is controlled between 5-10 seconds, and everyone can adjust according to their specific situation.

Electronic coffee machines with pre-infusion functions are relatively simple to operate—just set the desired seconds for pre-infusion time to achieve one-touch extraction. For manual coffee machines with pre-infusion functions, manual control of pressure and flow rate from the group head is required.

Phase 2: Flavor Compound Extraction

After pre-infusion ends, we enter the main extraction phase of coffee. At this point, the group head releases 9-bar pressure hot water to impact the coffee puck, and the pre-moistened coffee puck quickly dissolves coffee compounds. Under normal circumstances, coffee liquid will begin to flow out after the group head gauge reaches 9-bar following pre-infusion.

Initially, highly acidic compounds are extracted first, followed by sweet compounds, and finally bitter compounds. If you use three separate cups to collect the early, middle, and late stages of espresso, you'll notice that the early stage espresso has the darkest crema color, appearing brown, and is the most concentrated, with a sharp acidic taste when consumed. The middle stage espresso has slightly lighter crema, appearing golden yellow, with better fluidity and lower concentration than the first cup, tasting more balanced. The late stage crema is thin, appearing light yellow, and tastes lightly bitter-sweet, similar to barley tea.

Phase 3: Ending Extraction

When should espresso extraction end? What criteria should be used—time, liquid volume, or stopping extraction when the crema begins to turn white?

FrontStreet Coffee believes the basis for ending extraction should be a judgment based on all three factors. When the crema turns white, it's actually telling you that the desirable compounds in the coffee have been fully extracted, and you should stop extraction. Often, we end extraction even before seeing the crema turn white, because crema whitening means some less desirable flavors have been extracted, but we don't know if this quantity will affect the flavor. Therefore, we generally avoid this risk by ending early.

However, ending early also presents another problem—your espresso might lack the tail section. Coffee without the tail section will be very intense and have a short aftertaste. Therefore, you need to use time and liquid volume as auxiliary parameters for judgment. Time refers to the commonly mentioned 20-30 seconds, which is not a strict rule but just a reference standard...

Even with semi-automatic coffee machines that offer one-touch extraction, besides basic operations like dosing and tamping, you must understand the extraction process behind that one-touch operation. After all, this one-touch extraction also requires human programming.

Important Notice :

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