Precautions for Using Espresso Machines! What Are the Essential Factors Before Espresso Extraction? Why Should You Run Water Before Espresso Extraction?

Making espresso may look simple, but in practice there are a great many details that demand attention. FrontStreet Coffee says this often, and it is true: from distributing the grounds evenly during dosing, to applying consistent pressure when tamping, to steaming proper milk foam, everything has to be handled carefully to reach perfection.

Once you reach the extraction stage, there are even more details to watch. Among them is one step that many coffee enthusiasts still do not understand, yet experienced baristas always insist on doing it before extraction: releasing hot water beforehand.

The operation itself is simple. Open the water valve and release hot water for a few seconds before locking the portafilter into the group head, and only then begin extraction. Many people wonder what the point is. The answer is simple and comes down to two things.

The first is the reason everyone knows: cleaning the group head. After extracting coffee, some grounds can stick to the group head's shower screen, either from contact with the group head or from the machine's back-suction. Even if we clean the group head after extraction, residue can remain. Releasing hot water before extraction helps keep the shower screen cleaner and prevents extraction problems caused by leftover grounds.

The second reason is to ensure more stable espresso extraction. Without pre-flushing, the shot can show unexpected flavor variations. Look at the experimental comparison FrontStreet Coffee ran below.

Experimental Comparison

Both experiments used 20g of coffee grounds to extract 40ml of coffee liquid, and the only difference was whether a pre-flush was performed before locking the portafilter into the group head. At that moment the machine had not been used for over 30 minutes, which made the differences more apparent. (Do not ask why the machine had been idle for over half an hour. There were no customers.)

After extraction, FrontStreet Coffee tasted both espressos separately. The espresso without a pre-flush was more acidic and slightly weaker in flavor than the one extracted after flushing, while the flushed espresso tasted richer and more balanced. To make sure the assessment was accurate, FrontStreet Coffee measured the extraction rates with a coffee refractometer, and they came out at 20.44% and 21.07% respectively.

Small as the numerical difference seems, we could still detect quite distinct differences in taste. So why did the gap appear? The reason is simple: the water temperature during extraction was not consistent. The former was also affected by unstable pressure.

Why Pre-Flush is Necessary

As FrontStreet Coffee mentioned above, besides cleaning residue off the shower screen, another purpose of the pre-flush is to ensure more stable extraction. There are two main reasons extraction becomes unstable, and they may vary with the machine. One occurs when the machine has not been used for a long time, so the group head temperature drops from the lack of hot water passing through it. Lock the portafilter in and extract at that point, and the hot water flowing through will be cooled by those lower-temperature pipes, causing the extraction to deviate. The other comes from water in the boiler becoming hotter than the target temperature after sitting for a long time. Use that water directly and the coffee is likely to be over-extracted.

This issue affects not only older machines and current home espresso machines but also high-performance commercial machines. So to keep every parameter more stable during extraction, and with the added cleaning benefit, pre-flushing really is necessary.

FrontStreet Coffee Recommendation

Once your machine is dialed in, the remaining variable is the bean, and for espresso the choice usually comes down to a blend or a single origin. For a traditional Americano or latte, FrontStreet's Classic Blend and Commercial Blend are the obvious picks. Both build on an old-school Italian recipe with a small amount of Robusta added, so the shot gives butter, nut, spice, dark chocolate and toast aromas, a wild and heavy body, and generous golden crema that makes latte art simple.

If you are drawn to almond, walnut and apricot-kernel notes, FrontStreet's Signature Blend and Dark Cocoa Blend both contain a large proportion of Brazilian coffee, providing a comfortable bittersweet edge and a creamy peanut aroma with an exceptionally smooth entry. The Signature Blend adds Colombian coffee for nut, chocolate and caramel notes with a moderate acidity, while the Dark Cocoa Blend layers in the ripe plum acidity of Yunnan small beans and gives off a creamy chocolate aroma once ground, balanced enough for lattes, Americanos and all kinds of coffee specials.