Discussion on espresso: why the coffee grounds in the powder bowl can't be knocked out

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Put a dose of coffee powder ranging from 14g to 22g in a clean filter handle powder bowl. The specific amount of use depends on the capacity (different size) of the powder bowl and the amount and concentration of coffee you want to make. If there is too much loading, the filter handle cannot be fixed to the cooking head. Of course, it can not be loaded less, otherwise the top space of coffee powder will be too large, which will not only lead to cake-shaped coffee burnt, but also make the flow velocity unstable. At least at the beginning, remember to weigh the amount of coffee each time, so as to calculate the proportion of coffee when making a cup of coffee. Also, coffee powder may need more or more at this time.

Less redistribution, but first of all depends on how different types of grinders produce powder.

Flatten the coffee powder with a flat head press. The very fine powder directly received from the grinder is usually somewhat "fluffy". After flattening, it can not only drain the air in the gap, but also form a compact and flat cake to ensure uniform extraction as the water flows through. If the coffee cake is uneven, the water will flow to the place with the least resistance. At the end of the brewing stage, some coffee cakes with large water flow are overextracted, otherwise the extraction is insufficient. Compacting the coffee powder hard enough to drain the air from the crevice is the second goal. The deep or shallow pressure has no effect on the extraction rate, because the impact pressure of the Italian coffee machine on the coffee cake is 9 bar.

(58.5 kg / square inch), which is much stronger than the strength of human arms.

Few people care about stress when making espresso. Most machines can be set to a standard pressure of 9 bar (58.5 kg / square inch), and then you can let it go. Some modern Italian coffee machines have the function of directly regulating pressure in the process of brewing.

Coffee pressed powder can have high pressure under the condition of overdose.

This pressure is caused by pressing the shower head to the powder (or the powder top to the shower head).

When the amount of powder is slightly above the safety line, as long as the handle is locked, the shower head will press the powder.

Again, in fact, I think it has something to do with the pressure of coffee pressed powder. That is to say, there is a difference in velocity between tension and tightness.

The power lies in the coffee pressed powder itself. (not the contact surface between the cake and the showerhead)

Coffee pressed powder can have high pressure under the condition of overdose.

This pressure is caused by pressing the shower head to the powder (or the powder top to the shower head).

When the amount of powder is slightly above the safety line, as long as the handle is locked, the shower head will press the powder.

: so this pressure can be far greater than the pressure that can be exerted by ordinary people (1kg/cm2 at most)

This pressure minimizes the gap between powder particles, thus limiting the flow rate.

At the same time, it also limits the space for water absorption and expansion of coffee powder, and the proportion of porous expansion of coffee powder becomes smaller.

This also has a considerable effect on the flow rate in the middle and latter part of the extraction. (so that there is no change in the velocity of the front, middle and back)

I don't think it would be wrong to go up to the watershed, on the contrary, I think that's right.

However, if the shower head is overloaded, it will still have a bad effect.

It is like fracturing and crushing the powder particles, so that there is no room for them to absorb water and expand.