I believe baristas have definitely encountered this problem: in the morning, you dial in the espresso extraction parameters, but by noon, the parameters are off, and the coffee flow rate has noticeably slowed down.

Regarding this issue, Front Street previously offered explanations for two scenarios. The first is that on rainy days, when the air humidity is relatively high, the coffee beans in the hopper are prone to absorbing moisture. During grinding, they are also easily affected by water vapor, causing clumping and stale flavors in the coffee grounds, as well as unstable extraction.

The second is that when you adjusted the parameters in the morning, it was with the original coffee beans, but in the afternoon you topped up the hopper with new beans, so the extraction parameters need to be readjusted.

But if neither of the above two situations occurs, then the cause might be this — the inside of the espresso machine is too dirty.

When an espresso machine extracts coffee, a small amount of coffee grounds gets drawn back into the group head. If coffee is extracted continuously over a long period, a lot of coffee residue accumulates inside the group head. This obstructs the water flow from the group head, causing the coffee flow rate to slow down and become unstable. Moreover, long-accumulated coffee residue also affects water quality, giving the coffee off-flavors. 

So, before turning off the machine each time, you need to clean the inside of the group head. The method used is called "backflushing." First, we use a blind basket, which is a portafilter basket with no filter holes, so the water released from the group head has nowhere to go and can only return into the pipes inside the group head, flushing away the coffee residue left inside.

The specific operation is to lock the blind basket into the portafilter, and attach the portafilter to the group head just like when extracting espresso.

Then press the extraction button, let it extract for 10 seconds and stop, and the pressure release outlet will discharge dirty water containing coffee residue.

When you remove the portafilter, there will also be a small amount of dirty water with coffee residue in the blind basket.

What we need to do next is pour out the dirty water from the blind basket, lock it back onto the group head, and continue repeating the previous steps until the water in the blind basket is clear. Generally, repeating 5 times achieves this result.

Some barista friends might say, "I backflush and clean every day when I close up, so why does the extraction parameter still become unstable?" This is because it wasn't cleaned thoroughly. Some coffee residue is more stubborn and difficult to remove with ordinary water backflushing, so espresso machine cleaning powder is needed to solve this.

The method of use is to first pour 2-3g of cleaning powder into the blind basket, then lock it onto the group head, press the extraction button, and stop extraction after 5-7 seconds. At this point, the pressure release outlet will spray out white dirty water, which contains coffee residue.

Remove the portafilter, and the blind basket will have residual cleaning powder soaked in water along with coffee residue. At this point, you need to tilt it slightly to pour out the water and residue from the blind basket, keeping the water-soaked cleaning powder, then lock it back onto the group head, press the extraction button for 5-7 seconds, then remove the portafilter and pour out the water from the blind basket, then lock it back onto the group head, until the cleaning powder in the blind basket is gone when you remove the portafilter. Generally, repeating 4-5 times is enough.

Next, flush the group head with water without the portafilter, and use a brush to gently scrub the dispersion screen and the gasket. After cleaning the blind basket, lock it back onto the group head and repeat the water backflushing steps, though this time the purpose is to ensure the cleaning powder inside the group head is flushed out. Generally, repeat about 7-10 times.

The frequency of cleaning with cleaning powder doesn't need to be too high. Usually, water backflushing once a day and cleaning powder backflushing once a week is sufficient.

The above content is compiled by CoffeeHunters, a coffee news website.