Barista skills | "Professional barista Handbook" Espresso Grinding, Powder filling and cloth Powder

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Espresso grinding

Grinding is the process of tearing the cells of coffee bean particles in order to increase the contact surface between coffee solids and extracted liquids.

Why does Espresso need very fine grinding?

There are many reasons why high-quality Espresso requires very fine grinding:

It can create a very large area of particle surface area, providing a prerequisite for the rapid flushing of a large amount of solid material from the surface of the particle.

It can cut open more coffee granule cells, so that more macromolecular soluble matter and colloid can be extracted.

It allows water to enter the cell in a shorter average path, accelerating wetting (and diffusion), and bringing soluble matter out of the cell.

The smaller the particles, the larger the surface area, allowing them to gather more closely, providing the necessary flow resistance on the premise that the flow of water can pass through the powder bed.

Performance of bean grinder

The author suggests buying the best bean grinder you can afford, even if that means you have to reduce the budget of the espresso machine. In the case of high intensity use, an ordinary bean grinder will produce excess heat, caking, excessive ultra-fine powder and uneven distribution of coffee powder, resulting in uneven extraction and affecting the flavor of coffee. No matter how powerful the espresso machine is, it can't make up for the mess caused by a shoddy bean grinder.

One of the most important indicators of the bean grinder is the sharpness of the grinding plate, which cannot be overemphasized. The sharp grinding plate puts less burden on the motor of the bean grinder, emits less heat, produces less fine powder, and provides a better particle size distribution.

Tips: because of the high cost of buying new grinding plates on a regular basis, I suggest you find a local repair shop or bean grinder manufacturer that is willing to polish dull old grinding plates. The grinding plate can be re-polished several times before it has to be replaced.

How to evaluate a bean grinder

Family baristas rarely need to produce more than two to three copies of Espresso per hour, and may not notice how the performance of various professional bean grinders is different. Family baristas can use more time-consuming methods such as "Weiss Distribution Technology (Weiss Distribution Technique)" to make up for the shortcomings of general bean grinders (see the "trimming" section of Chapter 2 for details); they can also obtain stable and excellent flour through any qualified professional bean grinder.

Let's take a look at the coffee shop. Baristas often need to produce products quickly and continuously, so they need to be extra careful when choosing a bean grinder. A professional barista needs a bean grinder to help him spread the powder evenly and will not overheat the coffee powder under high intensity.

Here are some important conditions for evaluating the bean grinder.

Minimize the heat generated by grinding. During grinding, some heat is inevitably generated due to friction and the tearing of molecular bonds, but we do not want the coffee powder to be heated by the heat generated by the bean grinder. Because these calories will destroy the flavor of coffee and accelerate the volatilization of aromatic substances. It will also cause oil to flow out from the surface of the coffee particles, making the coffee powder form sticky lumps. (note 2: the author encountered this problem when using a small flat knife grinder, and when checking the used pressed powder, it was found that 20% of every pressed powder was completely dry. ), resulting in unstable extraction. Caking will hinder the wetting of the coffee powder, so that after the extraction, there are large chunks of dry parts in the powder bed.

A well-designed bean grinder should not have a narrow or airtight space that will intercept and conserve heat under high intensity use. Sharp grinding plate, low-speed motor, large-size "practical" grinding disk surface, can ease the heat generated in grinding. It is mentioned here that the plate should be "practical because some bean grinders are too far apart when crushing coffee beans, and most of the area of the plate is ineffective." The larger the grinding plate and the more practical the design, the more conducive to the dispersion of heat.

Appropriate particle size distribution. The design of commercial Italian bean grinder mostly tends to the particle size distribution of bimodal curve (or three-peak curve). This means that there are 2 (or 3) particle sizes in addition to the largest proportion of particle sizes. In this distribution, the thicker particles create an appropriate flow velocity, while the finer particles provide a large enough area of particle surface area for high-speed extraction. As mentioned above, the sharp grinding plate optimizes the particle size distribution, while the blunt grinding disc makes the particle size distribution more uniform.

Refuse to agglomerate. A bean grinder must be able to avoid caking of coffee powder. If you want to test your bean grinder, you can grind two or three portions of Espresso coffee powder and spread it on a piece of paper to see if there are any protruding lumps. Once caking is found, the grinding plate needs to be cleaned, as does the channel between the grinding plate and the powder cartridge; if the grinding plate has been worn, the grinding plate needs to be replaced. After doing this, if the bean grinder continues to agglomerate, you can try the Weiss distribution technique (see the "trimming" section of Chapter 2 for details).

Caking also increases the amount of heat generated during grinding, and if the bean grinder designs a small channel between the grinder and the powder cartridge, it will force the coffee powder to be barely squeezed out of the channel. And when using stale beans or re-baked beans, it will make the coffee powder surface very greasy.

It is easy to distribute powder evenly. Many baristas have pioneered some clever ways to make the cloth more uniform, but a good bean grinder should be able to evenly distribute the powder even without relying on the barista's skills.

There are some flour receiving devices that can promote the uniformity of the cloth powder, which is difficult for even the most skilled baristas to match. If you want to spread the powder evenly, you need a bean grinder to make the ground powder fall straight into the powder bowl instead of falling sideways. And to avoid the emergence of "furry" coffee powder, or install homogenization (mixing) device.

Grinding mechanism: pre-grinding or on-demand grinding

Most commercial bean grinders are designed for pre-grinding. Coffee cartridges are kept full of coffee powder at all times, and baristas can get the expected amount of powder immediately by simply poking a pick or two. This mechanism seems to be fast and convenient, but it has two major defects: first, the weight of each filling is affected by the coffee powder content in the powder cartridge, and the coffee powder content in the powder bin changes from time to time; second, the business quality makes the coffee powder exhaust time will be long and short.

Exhaust is the gradual release of gases from coffee, mainly carbon dioxide produced during baking and some volatile aromatic hydrocarbons (3:1 grams of fresh Arabica beans contain 2-10 milligrams of carbon dioxide, the values in most reports are close to the lowest values in the above range. It takes weeks for coffee to remove most of its carbon dioxide in whole bean form, while coffee powder takes several times faster. One study has shown that 45% of carbon dioxide stored in freshly cooked beans is released within the first five minutes of grinding. The standard Espresso grind is finer than the coffee powder used in that study, so carbon dioxide emissions will be faster. After the coffee is ground into powder, the exhaust process will be significantly accelerated.

Coffee powder contains the right amount of carbon dioxide is very important, because it can affect the flow rate of water during filtration. Coffee powder releases a lot of carbon dioxide when it comes into contact with hot water. (note 4: when it reaches the cooking temperature of Espresso, carbon dioxide is more soluble in water under high pressure. In the process of extracting Espresso, the pressure at the top of the powder bed is the highest (usually 9 atmospheric pressure), while the pressure at the bottom of the powder bed is the lowest (normal atmospheric pressure). In the process of the extracted liquid flowing through the powder bed, the pressure is getting smaller and smaller, so the exhaust effect occurs more frequently in the lower part of the powder bed. However, in the low-pressure pre-immersion, the whole powder bed can produce a large amount of exhaust), which can wash back the surrounding liquid, increase the flow resistance and slow down the flow rate.

When using the pre-grinding mechanism, because the amount of carbon dioxide retained in the coffee powder is not fixed, the flow rate is not fixed each time. The unfixed flow rate eventually leads to the instability of coffee flavor, alcohol thickness (Body) and concentration.

On-demand grinding is better than pre-grinding because each serving is freshly ground coffee powder, which retains more aromatic hydrocarbons and provides a more fixed flow rate, because the content of carbon dioxide in each serving of coffee powder is fixed. The only disadvantage of on-demand grinding is that it takes longer to produce.

Adjust the degree of grinding

In the daily business process, the factors that have the greatest impact on each product are grinding and powder filling. As long as the amount of powder is reduced by 1 g, the fixed flow rate can be changed immediately. Therefore, baristas should not adjust the degree of grinding just because there is a problem with the flow rate of a certain product, which may be caused by a difference in the amount of powder filled with the previous product. On the other hand, when the flow rate of several consecutive products tends to become faster or slower, baristas should be sure that it is necessary to adjust the degree of grinding.

To maintain consistent powder filling, baristas should do:

1. Through practice, each product can achieve the same filling powder, cloth powder, trimming (smoothing, strengthening of cloth powder).

two。 Through practice, the weight error of each powder bed is less than 0.5g.

3. The periodic period weighs the fillings of several different products during peak hours to test the stability of baristas.

When adjusting the degree of grinding, it is best to make a small adjustment. If your bean grinder has a small channel between the grinder and the powder bin, wait for about 5g of powder to come out each time you adjust the grinding degree, and then make an observation. This can eliminate the influence of "residual powder" that remains in that small channel or scattered in the powder cartridge.

Baristas should adjust the bean grinder as little as possible and do not change the scale every time it is produced.

Filling powder and cloth powder

Different from other coffee professionals, the author believes that filling powder and cloth powder is a whole link, because most of the time, the cloth powder of the powder bed has already been completed when filling powder. The barista's goal in the powder filling and powder distribution phase is to provide a consistent amount of powder filling for each product, as well as a uniform distribution of volume and density. The difference in the amount of powder filling will lead to the change of flow rate, and the uneven distribution of powder will lead to uneven extraction.

If baristas can only have one of the most important skills, it is also consistent to create a powder bed with uniform cloth powder. Once the powder filling begins, the cloth powder begins, so careful powder filling is the key.

How to fill powder

The following is an example of a powder filling process:

1. Remove the handle from the espresso machine.

two。 Knock out the used pressed powder.

3. Dry the inside of the powder bowl with a dry rag. If there is water left on the edge of the powder bowl, it will make the edge of the powder bed produce a channel.

4. Make sure that every filter hole in the powder bowl is empty.

5. Start the bean grinder. If the grinding speed of your bean grinder is very slow, you may need to start the bean mill in the first step.

6. Repeatedly circle with the handle to make the coffee powder fill the bowl as evenly as possible. If one area has more powder than another, the area with more powder will be more compact, even after trimming.

7. After grinding the right amount of coffee powder, turn off the bean grinder.

8. Stop filling powder when the powder in the bowl has reached the expected amount. This amount can be exactly the amount of powder needed for extraction, or a little more, and the excess powder can be removed during dressing. No matter how much powder you choose, the most important thing is to keep the same amount of powder in each serving.

The skill of filling powder

No matter which powder filling technique you use, sprinkling only a little powder each time you move the handle is always easier to get a uniform cloth powder than dropping a large amount of powder. Using one or two powder filling techniques can improve the work efficiency of a busy cafe.

1. The cake filling method. Think of the powder bed as a cake, cut into wedge-shaped pieces. When filling powder, aim at the powder bowl, fill each "small piece" separately, and fill the next adjacent piece by moving the handle. Move, fill, and repeat in this order.

two。 Stratification method. When receiving the powder, sprinkle a small amount of coffee powder from the edge of the powder bowl, and constantly circle with the handle to form a shallow and uniform layer of coffee powder. Repeat this action to build the second layer on the first layer. Keep raising the floor until the amount of powder in the powder bowl reaches the desired target.

↑ forms a powder layer by constantly circling it with a handle, always filling it at the lowest point of the powder bed.

Trimming

The barista should trim the powder after filling and before pressing the powder. The dressing process includes redistributing the powder on the top of the powder bed (for the entire powder bed when using the Weisscloth powder technique), removing excess coffee powder when the barista thinks there is too much powder, and smoothing the surface of the powder bed before pressing it.

Techniques for trimming

Nowadays, many common dressing techniques are widely used, each of which has its own advantages and disadvantages.

1. North-South East-West (NSEW) method (don't be confused with the powder pressing technique of the same name). North, South, East and West methods are easy to learn and fast enough for busy cafes.

Use your fingers or ruler to push the stack of coffee powder toward the farthest part of the bowl (that is, the "north"). Don't push over the edge of the powder pile. Then push to the near side (south), then to the right, then to the left. Finally, push all the extra powder out of the edge. At this time, the surface of the powder bed should be smooth and smooth, without any trace or obvious difference. The point of using the NSEW method is that the amount of "excess" powder that needs to be trimmed each time is fixed. The weight of coffee powder piled up before dressing has a great influence on the density of the powder bed after dressing. Although the final results all look the same, the powder beds with more powder piled up before finishing will have a higher density after dressing.

↑ first pushes the powder pile to the far side of the bowl (north), then turns back (south), then to the right (east), and then to the left (west), pushing all the excess powder out of the edge before pressing the powder.

two。 Stoke Fleet shift method (Stockfleth's Move). The Stoke Fleet movement may be the most difficult trimming technique to master, but it is especially easy to use after mastering it. First of all, make the powder bowl slightly overfilled with powder. With both elbows outward, hold the handle in front of the torso. Hold out a straight finger, or from thumb to index finger, and gently place it on the powder pile. Turn the elbow in so that the handle and the hand move in the opposite direction. At this point, the stacked coffee powder will move around the center of the powder bowl. Repeat this action until all areas are filled and pressed. Before pushing the excess powder out of the edge, you can also use the NSEW method to smooth the surface of the powder stack.

↑ first let the elbow outward, and then to recycle the elbow, so that the stack of coffee powder moved toward the center of the powder bed. Repeat this action 2 to 3 times.

↑ pushes the excess coffee powder out of the edge before using the NSEW method.

3. Weisbu powder skill (WDT). Pioneered by JohnWeiss, WDT has a magical effect on caking and uneven cloth powder. The first step in operating a WDT is to insert a funnel from the top of the powder bowl (John recommends using a small yogurt cup with the bottom cut off). Put the coffee powder into the powder bowl until there is a little overflow. Stir the coffee powder evenly with a slender pointed object (such as a long needle or a straightened paper clip). After the funnel is removed, the powder pile is repaired by NSEW method or Stoke Fleet moving method, and then pressed powder. Another way is to put the coffee powder in a separate container, stir it and then fill it into a powder bowl. This method allows the handle to be separated from the cooking head for a shorter time, so it allows the powder bowl to maintain higher calories.

There are two great advantages to using WDT, which is that after the coffee powder has been filled into the powder pile, it can also break the cakes and redistribute the whole powder pile. The downside of WDT is that it may be a little too time-consuming for busy cafes.

↑, ugh! A lot of caking! Use a straight paper clip to stir violently to break the cakes, and finally get fluffy, non-caking coffee powder.

Trim a shallow pile of powder

All the trimming techniques mentioned above are based on enough coffee powder to fill the powder bowl. When the amount of powder does not reach the edge of the powder bowl, it cannot be trimmed with fingers or tools. To trim a powder pile with less powder, baristas have two options: one is to use a curved tool, and the other is to change to a smaller powder bowl (Note 5: use the curved tool to trim the powder bed, the surface will be sunken. After pressing the powder, the density around the powder bed will be higher than that in the central area, which is actually not ideal. However, because the channel is most commonly found in the area around the powder bed, this part can prevent one of the factors that are most likely to produce the channel. Powder beds trimmed with curved tools rarely produce large channels, and the final products are usually good, but not perfect).

↑ uses the lid of the powder cartridge or other curved objects to trim the shallow powder heap. The greater the Radian of the curved surface (or the smaller the object of the curved surface), the better it is to handle a smaller amount of powder.

Shallow piles of powder can be trimmed with raised curved tools (such as the lid of the powder compartment of a bean mill). You can place the tool on the edge of the powder bowl, use the NSEW method to slide the tool, and then push the excess powder out from the edge. You can also place the tool on the centerline of the powder bowl and turn it around or two in a way similar to the Stoke Fleet movement. The excess coffee powder can be extruded from the edge of the powder bowl using a curved tool.

When using smaller powder bowls, there is no need to prepare specific dressing tools. For example, 15g of powder may be too shallow for a double bowl, but a double bowl from another manufacturer may be flush with the edge. If you are used to using straight ruler-shaped tools for trimming operations, it is worth having different sizes of powder bowls.

Chapter 2, the strength of powder pressing, how to press powder, to be continued.