Technical Post: The Effect of Stirring in American Pour-Over Coffee Extraction

Have you tried coffee brewed in an Americano pot? You will find that for the same coffee beans, the coffee brewed in an Americano pot is obviously more bitter and astringent than the coffee brewed by hand. The key is that the water temperature of the Americano pot is high, which causes this phenomenon. In general, the Americano pot uses atmospheric pressure to spray and extract. In short, when the power of the Americano pot is constant and the external environmental factors do not change much, the extraction water temperature and water flow rate are relatively stable, and the extraction temperature is too high and the water flow rate is slow, so there will be over-extraction. This is how bitterness comes from, and Americans like this kind of bitterness.

There are differences between American and Japanese styles. Although both American and Japanese styles may use the same filter cup, there are some differences in coffee bean roasting, grinding, filter paper, water temperature and techniques.

The biggest difference is that American hand-brewed coffee requires a stirring rod to stir the coffee powder while brewing, which is somewhat similar to the stirring method we use when making a siphon pot; while Japanese, Korean, Taiwanese and domestic hand-brewed coffee only uses water to draw circles, and never uses a stirring rod or bamboo stick to stir the coffee powder.

The typical American flavor is mainly based on medium roast and dark roast, with strong + mild bitterness + sweetness. It has both bitter and sweet characteristics. Grinding medium roast medium grind, water temperature between 80-85 degrees, water pouring speed medium speed. Dark roast is finely ground, water temperature between 85-90 degrees, slow pouring, bitterness is stronger, Americans often drink a cup in the morning to wake up quickly, also known as "dawn coffee".

[American brewing is simpler]:

First, the flour must be ground very finely, basically the same as Italian flour;

Second, the water temperature is around 90 degrees;

The third is stewing and steaming, which is similar to the Japanese style;

Fourth, pour water slowly in circles while constantly stirring with a wooden spoon or bamboo stick. There are different ways to stir. One is to stir back and forth and left and right; the other is to stir in circles.

There are four important points for extraction:

<1>, grinding degree, powder ball size, the fewer powder balls, the higher the extraction rate (the powder balls are small, but the quantity is large, the surface area in contact with water is large), so when the taste is not enough, the easiest way is to adjust it finer.

In view of the above two points, it can explain why poor grinding is easy to produce foreign taste, because there are more ultra-fine powders, which locally increases the extraction rate, resulting in foreign taste.

<2> Time. When other parameters are the same, the longer the time, the higher the extraction rate. This is known to everyone.

<3>. Stirring and adding external force will increase the extraction rate, whether through additional containers or through water flow.

<4> Temperature: different water temperatures for beans of different roasting degrees

Steaming and stirring method

Steaming and stirring method : Stir with a stirring rod. Usually, a cross stirring is performed during the steaming stage to allow the water to fully contact the coffee powder and increase the release of aromatic substances. The subsequent methods vary. Some people stir in a circle after the first, second or third stage of water injection. Some people stir after the first knife flow, and some people stir at all three stages. As long as the control is appropriate, all methods are acceptable.

This method can effectively increase the release of aromatic substances and also has a significant effect on the special flavor. The disadvantage is that it is difficult to control the degree of stirring. If you stir too much, it will have a harsh and sour taste, and if you stir too long, it will be bitter, and the strength must be gentle.

Advantages : The stirring method can amplify the advantages of the coffee beans, especially enhance the taste of the coffee beans, and not be too thin.

Disadvantages : Although its flavor is more obvious, its aftertaste is much weaker . Moreover, this method requires high quality of coffee beans. If inferior coffee beans are used, it will only infinitely magnify its bad flavor. In addition, since this method requires very fine grinding of coffee powder and sufficient stirring, it is easy to over-extract if not properly controlled.

In my opinion, making coffee is a trivial thing. It is always interesting to forget the form and try new methods. Stirring brewing is simple, common and cool.

1. In the steaming stage, the water volume is steaming and stirring > direct water injection > standard steaming; in the later stage, it is direct water injection > steaming and stirring > standard steaming; however, if the initial steaming water volume is 50 grams (corresponding to 20 grams of powder), then the entire instantaneous water volume trend chart will be different; the amount of water injection in the steaming stage will determine the instantaneous water volume trend in the later stage of brewing, so the instantaneous water volume trend chart in the article will also change.

2. From my experience of steaming and stirring, I would use a shorter extraction time than the standard hand-poured method (because stirring accelerates the possibility of uniform extraction, so there is no need to use such a long extraction time). In your experiment, steaming and stirring = standard steaming = direct water injection in terms of extraction time. This method of limiting the same extraction time is of course likely to lead to the view in the article that "coffee made by steaming and stirring is more turbid and dull". Because the coffee may be over-extracted.

How to stir to make delicious coffee

Recently, we have found that many people have begun to add the action of stirring with a wooden stick during the process of hand-brewed coffee. This can't help but arouse our curiosity. In the process of hand-brewed coffee, isn't the coffee powder already being stirred by water flow? Is it necessary to stir it with a wooden stick?

When I asked this question, I decided to prove it through experiments.

According to the extraction principle, if the water and extract are at the same temperature and the same disturbance is used at the same time, the same solution should be extracted. We do not think that coffee will have the same results at the microscopic level, but after many experiments, we can summarize a certain flavor trend. Therefore, we designed the following three methods for experimentation:

1. Direct water injection method: spiral water injection method without continuous water and steaming

2. Standard steaming method: steam for 30 seconds (medium baking) and then spirally inject water

3. Steaming and stirring method: Steam for 30 seconds (medium baking) and stir with a wooden stick for 10 seconds during steaming, then continue to spirally inject water

During the experiment, the grinding degree, powder amount, water-to-powder ratio, total water injection time, and water temperature of each coffee bean were equal. The three brewing processes were:

Direct water injection method: inject 320g of water at a uniform speed throughout the process. The water injection time for medium roasting is 2 minutes, and the water injection time for deep roasting is 1 minute and 30 seconds.

Standard steaming method: first add 20g of hot water, steam the medium roasted coffee powder for 30s, then add water at a constant speed and finish in 2 minutes;

Steaming and stirring method: first inject 50g of hot water (too little water will make stirring impossible, so 50g of hot water is injected during the steaming time), stir to make the water and coffee powder contact evenly, steam the medium roasted coffee powder for 30s before adding water, and complete the water injection in 2min; steam the deep roasted coffee powder for 15s before adding water, and complete the water injection in 1min30s.

When discussing from the perspective of sensory perception and data, it is difficult for us to explain why the direct water injection method and the steaming and stirring method have two extreme flavor tones even though the numerical difference is not large. From the results, we can only infer that the steaming and stirring method accelerates the extraction of flavor substances in a shorter time, dissolves some heterocyclic macromolecules, and causes a more turbid taste; the water flow in the direct water injection method also has an effective stirring effect and effectively increases the extraction rate of small molecular acidic substances, so it shows a brighter sour feeling in terms of sensory perception. We sincerely look forward to more advanced experiments to help explain the essential differences between the two stirring methods.