What is the principle of Rao hand brewing coffee? what is the effect of rotation on coffee extraction?

In the world of hand brewing in Europe and the United States, many well-known baristas admire the hand brewing technique of Rao (Rao Spin), which is used by at least three world coffee brewing champions.

The rotation method is said to have been invented by Scott Rao, who has a reputation as a global barista soul mentor, but he denies it, saying there is someone else.

What exactly is the Rao technique and why it is highly regarded by the boutique coffee industry?

Today, through the Rao-style rotation instructional videos of three international hand-chug masters, the coffee commune will carefully talk to the partners about the tricks of the Rao-style rotation method, the scientific principle behind it, and how to operate it correctly, so as to avoid the misunderstanding that drawing a tiger does not turn into a dog.

Hope that interested people can rest assured to practice Rao-style skills, so that the flavor of the hand, please climb to another high-rise building!

Who is the inventor? Everyone thinks Rao invented the rotation method.

Scott Rao is known as one of the top three barista mentors in the world, along with James Hoffmann (winner of the 2007 WBC World Barista Competition) and Matt Perger (winner of the 2013 WBC World Barista Competition).

Coincidentally, the above three soul mentors in the global coffee industry are all shooting films to teach this "Rao Spin" rotary brewing method.

But because Scott Rao didn't want to take credit, he wrote a blog post called "Why spin Coffee?" At the beginning of the article, he solemnly announced that he was not the inventor of the rotation method, and he believed that James Hoffmann should be the first to use this technique.

Scott Rao clarified that he did not invent the rotation method.

But as Scott Rao mentioned in this blog, he demonstrated this technique, and everyone did it, and found that it really worked. Because the entry barrier of this rotation method is not high, you can learn it as soon as you learn it, and the flavor after rotation has been successfully improved almost every time, so this technique has become very popular.

What are the benefits of R ao rotation? Why let beginners be fascinated as soon as they learn?

Characteristics of Rao rotation method

Insufficient extraction calls for Rao technique to release the hold-up.

The R ao rotation method helps to improve the extraction rate and solve the problems of insufficient extraction and uneven extraction, which are the most headache in hand-brewed coffee.

The so-called extraction rate refers to the dissolution rate of flavor substances after coffee powder comes into contact with water. According to the golden cup law of hand-brewed coffee, the extraction rate of delicious coffee should fall within the golden percentage range of 18-22%.

The picture below is the coffee gold cup rule table (Golden Cup Ratio) published by the Fine Coffee Association SCA. The horizontal axis in the table represents the extraction rate, that is, the dissolution rate of coffee.

Gold cup law of coffee extraction

Although the golden cup law recommends the extraction rate of a good cup of coffee, we often take care of one thing and the other in practice. Or take into account the extraction rate of 18%-22%, but because of uneven extraction so bitter. Otherwise, the extraction rate is too low, because the extraction is insufficient, so the coffee is as light as clear tea, plain, acerbic and tasteless. If the coffee is always insufficient or uneven, even if you buy high-priced boutique beans, it is just a waste of a bag of good beans, because you can smell them, but you can't drink them all. Therefore, the R ao technique can solve the two major problems of deficiency and inequality at once, no wonder it is very popular.

Next, let's talk about the implementation of R ao technique, and then explain its scientific principle.

Operation demonstration of Rao technique

The first time is in the steaming stage (from 5 minutes to 50 seconds), he gently adds hot water that weighs twice as much as beans, then puts down the hand flushing pot, holds the upper filter cup and the lower seat sharing cup with both hands, and then "rotates" his hands together. Let the coffee grounds and water mix evenly into a muddy shape. After confirming the mixing, put down the filter cup and the sharing pot and wait for the steaming to end.

At the stage of water injection, James Hoffman performed two water injections. For the first time, 60% of the total water is poured, and the remaining water is slowly injected into the filter cup to maintain the highest water level in the filter cup so that it does not exceed or reach the highest position of the first water injection. After injecting all the water, James Hoffman once again used the rotation method.

R ao rotation can go back to the clock, can be clockwise, there is no limit, but the rotation needs to hold both the sharing pot and the filter cup. After grasping firmly, rotate the coffee slurry with the strength of your wrist, and the rotating force can be gentle or strong. Rao rotation method is especially suitable for V60 cooking.

What is the magic of this rotation method that makes everyone admire it so much?

It turns out that the rotation of the coffee filter cup will form a centrifugal force, and the centrifugal force can just solve the problem of "channel effect (the channeling of water)" that often occurs in hand-brewed coffee.

Next, let's first explain the scientific principle behind the R ao rotation method.

The scientific principle of rotation method

The dry coffee wall leads to insufficient extraction.

Coffee can be extracted unevenly, usually because a towering dry coffee wall is formed on the side of the filter cup wall, or an uneven coffee bed is formed at the bottom of the filter cup.

Why is coffee easily piled on the wall or unevenly deposited at the bottom? It is mainly caused by too fast or unstable water injection.

Water injection is a skill that needs to be practiced. Stable and gentle water injection requires long practice and calm cooking. Before practice makes perfect, poor water injection can easily cause the problem of uneven extraction.

At the beginning of learning to brew coffee Xiaobai, when the muscles are not trained to apply a correct force and memory, the control of water flow is often large and small, fast and slow, strong and weak, high and low.

Unstable water flow, resulting in uneven density of coffee powder layer accumulation problems, as well as towering dry coffee walls, naturally lead to uneven and insufficient extraction.

Uneven accumulation of coffee bed to form channel effect

Uneven bed surface, so that the bottom of the coffee powder accumulation density is inconsistent, some places loose, some places tight. Different thickness or density will affect the flow rate of water as it passes through. Where the density is low (or where the thickness is thin), the flow rate is faster, and where the density is high (or where the thickness is high), the flow rate of water is slow. The coffee powder bed with fast flow rate is easy to lack of extraction, and the coffee powder bed with slow flow rate is easy to overextract, so as long as the bed surface is inconsistent, it will lead to uneven extraction.

The penetration speed of water varies on the uneven bed.

How to avoid the uneven extraction caused by accumulation on the wall or uneven subsidence? Through the centrifugal force produced by rotating coffee, the fastening can be released.

When rotating coffee, the rotating coffee pulp is affected by centrifugal force, and every drop of water and every coffee particle is subjected to a force that pushes it outward, adding a horizontal force.

Centrifugal force helps coffee powder receive water evenly

Under the action of no centrifugal force, when water is injected into the coffee powder bed, if the water injection force is uneven, the speed of receiving water in each area of the coffee powder bed is uneven.

Rotating coffee liquid, the strength of centrifugal force increases with the weight of the object. At this time, because water is heavier than coffee powder, the horizontal migration force of water increases with the help of centrifugal force.

The centrifugal force of the rotation method operates properly, we can let the water quickly and horizontally penetrate each coffee powder horizontally, so that all coffee is evenly watered (saturated), avoiding the uneven drying and wetting of the coffee powder.

Usually dry coffee powder is more likely to cause channel problems (because water tends to be inaccessible). Therefore, rotation helps to improve the uniform water reception of coffee powder and reduce the channel effect.

Centrifugal force helps to form a flat coffee bed

In addition, centrifugal force also helps to distribute the coffee powder more evenly before the coffee powder settles down, so it is easier to form a flat coffee bed when it sinks to the ground.

The flat and uniformly arranged coffee bed avoids the generation of channels and results in a more average extraction rate. if coffee powder can be extracted more evenly, there will be no acid-sweet imbalance or even bitter over-extraction.

However, centrifugal force is not a panacea, improper operation may be counterproductive.

Too much centrifugal force is counterproductive.

The minus effect of centrifugal Force

The centrifugal force is so easy to use, so I shake it for a long time after injecting water to make the coffee liquid turn faster? Can you shake it more evenly in this way?

I'm afraid not, the use of centrifugal force must be "just right", otherwise insufficient extraction and over-extraction may occur again, but this time it is caused by centrifugal force.

If the centrifugal force is too strong, the coffee particles stick to the wall.

If the centrifugal force is used too much, it will cause the problem of sticking to the wall of large granule coffee powder. Because the coffee with large particles is heavier, under the acceleration of centrifugal force, the coffee with large particles can break through the water resistance and be thrown to the wall of the filter cup. As for the fine powder, because of the deceleration effect of water resistance, it begins to sink when it is kept near the center.

So excessive use of centrifugal force, but using centrifugal force to classify coffee according to its weight and particle size, the heavy ones move closer to the periphery and the light ones concentrate in the middle.

The result of grading the particle size in this way is that when the water falls in a flat way and flows out of the coffee powder layer, the large particles in the periphery have a fast penetration speed because of the more water in the gap, so the extracted material is less, the density of the small particles in the middle is high, and the penetration of water is slow, so more matter is dissolved.

If the fine powder extracts too much, it is easy to dissolve the bitter substances, the large granule water is filtered too fast, and the flavor substances are extracted too little (and the acid dissolves first, but the sweet is too late to dissolve). It is conceivable that the flavor in such a cup is sour, bitter and low sweetness.

Rao style rotation invincible secret skill

After talking about the scientific principle of the R ao rotation method, and after paying attention to the use of centrifugal force, let's summarize the operation secret of R ao rotation.

First of all, let's take a look at the film made by Scott Rao himself. He also uses a V60 filter cup. Let's see how he uses rotation to make coffee.

Generally speaking, Rao rotation method is suitable for fast-flow conical design of filter cup, and it is also suitable for continuous boiling with one knife.

Because the tapered filter cup is characterized by narrow mouth and thick powder layer in the center. If you don't have enough water injection skills, it's easy to push the powder to the wall and you can't eat water.

Then the tapered filter cup because the central powder layer stack is very thick, if the powder layer depth is not infiltrated enough, the channel effect is easy to occur. Therefore, it is necessary to rely on the rotation method to improve the average water capacity of the coffee powder layer.

As for the suitable one-size-fits-all flow, it is because there is enough water to drive the rotating force. if it is divided into multiple stages of water injection and rough grinding, the water may not have been picked up and turned, and the water has been filtered dry.

Do you use a tapered filter cup? Are you experiencing the problem of uneven or insufficient extraction? Is your coffee wall thick and your coffee bed uneven?

If you meet the above conditions, I think R ao rotation should be quite suitable for your hand punching technique. Would you like to try it? May you be invincible, and we'll see you next time.