Coffee Extraction Series | The Effect of Coffee Powder-Water Ratio on Coffee Extraction Flavor

As a universal solvent, water plays a vital role in coffee extraction. Today, we will not discuss the effect of water quality on extraction, but the effect of the ratio of coffee powder to water on extraction.

In daily coffee shop production, the most common ratio of coffee powder to water is 1:15. Some Japanese brewing coffee shops often use 1:12. How do we determine what ratio we should use for extraction?

#Gold Cup StandardGold Cup Standard

According to the definition of the SCA (Specialty Coffee Association) Gold Cup Standard, when the concentration of a cup of coffee is between 1.15%-1.45% and the extraction rate is between 18%-22%, it is considered to be coffee that meets the Gold Cup extraction requirements.

The coffee extracted by Golden Cup basically meets the taste of most people, and it has become one of the standards for good coffee. According to the Golden Cup standard, the best coffee powder to water ratio should be: 1000ml water, 50-60g coffee powder

▲Concentration diagram

The Gold Cup provides a general direction and reference, but it is not the only standard. Normally, I will use the Gold Cup criteria as a tool, which I will write about in a subsequent article.

If you want to determine the amount of water while keeping the amount of coffee powder unchanged, you must first know how the change in water affects the concentration and extraction rate, and then what the impact is on the flavor.

▲Schematic diagram of the gold cup

Below are two sets of data, one for immersion extraction (cup test) and one for drip extraction (hand pouring)

▲Immersion extraction data

▲Drip extraction data

Immersion extraction has relatively few uncontrollable factors and is more stable. However, drip extraction does not rule out some uncontrollable factors and human errors, but the control parameters of the experimental samples vary greatly and will not affect the trend of the data, so the errors are temporarily ignored. (See the table above)

From the table, we can see that no matter whether it is immersion or dripping, when other extraction parameters are the same, as the amount of water increases, the extraction rate will increase accordingly and the concentration will decrease; conversely, as the amount of water decreases, the extraction rate will decrease accordingly and the concentration will increase .

Why is this happening?

First of all, coffee extraction is a process of transferring from high concentration to low concentration. Taking immersion as an example, when other parameters are the same, the less water, the easier it is for the solution to be saturated, so the concentration transfer becomes slower; when the water volume is large, the solution concentration is low and the concentration transfer is faster. Therefore, under the condition of fixed time, the extraction rate is higher when the water volume is large, and the extraction rate is lower when the water volume is small.

The situation of drip extraction is slightly different from that of immersion extraction. Drip extraction is from top to bottom, and actually every drop of liquid that falls into the lower pot has nothing to do with the extraction process. Take the 300g water injection sample as an example. When the liquid dripped into the lower pot reaches 200g, the liquid dripped into the lower pot reaches 200g compared with the sample with 255g water injection. Excluding uncontrollable factors, if the water injection is stopped at this time, theoretically their concentration and extraction rate should be similar. In the test, the 300g water injection sample continued to be injected with water, which resulted in the water in the latter part increasing the overall extraction rate. Since the soluble matter in the latter part of the coffee powder is already less and more difficult to extract, the concentration of the liquid dripped into the lower pot in the latter part is much lower than the 200g liquid in the former part, thus diluting the entire pot of coffee liquid. It can also be said that the 300g water injection extraction sample consists of two parts of liquid.

▲Liquid segmentation

Comparative flavor (immersion and dripping have the same flavor trend): when the amount of water is reduced, the body is higher, the flavor is concentrated, the acidity is higher and sharper, and the aftertaste is insufficient; when the amount of water is increased, the taste is thinner and even watery, woody, slightly astringent, and the flavor is weak; when the amount of water is moderate, a relatively balanced state is reached, with a rounded taste, soft acidity, stronger sweetness, and a more layered flavor display.

▲Flavor diagram

I believe everyone already knows the impact of changes in water volume on concentration and extraction rate, and then what the impact is on flavor.

But the most difficult part is how to change the amount of water according to the characteristics of the beans, and how to control the degree of change in the amount of water during the debugging process. According to this method, by controlling the variables and doing comparative brewing according to different coffee beans, you can quickly master it.

For example, for medium-dark roasted coffee beans with low acidity, we can reduce the amount of water to increase the concentration and reduce the extraction rate, so as to achieve a mellow taste without producing a burnt bitter taste due to over-extraction; and for medium-light roasted coffee beans with high acidity, by increasing the amount of water to reduce the concentration and increase the extraction rate, the flavor is fully displayed, the layering and sweetness are enhanced, and the acidity becomes softer. For relatively stale beans, we can also reduce the amount of water. The most important thing is to make changes according to your own flavor preferences, but remember that in the extraction stage, the barista can only try to cover up the defective flavor of the coffee beans and show its good flavor. There is no way to "create something out of nothing". For example, if you want to increase the mellowness of a very lightly roasted Kenya to the same level as Mandheling and reduce the amount of water, the coffee will become sour, which is counterproductive.

In the extraction stage, the factors that affect the final flavor are not only the powder-water ratio. Therefore, in the extraction process of water volume comparison test, if there are no other commonly used parameters, you can test it according to some parameters of cupping. Water temperature 92℃, cupping grinding degree (850μm sieved 70%), powder amount (hand brewed coffee is recommended to use 15g).

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If you are not sure about the powder-water ratio for the first time, here is a rough method: first set the required concentration and extraction rate according to the basic characteristics of the beans, and then use the simple extraction rate calculation formula to calculate the amount of water used for extraction.

Extraction rate % = coffee concentration % * coffee liquid weight g / coffee powder weight g

Suppose you want to make a cup of mellow Mandheling, we need a high concentration and low extraction rate. Take a random concentration of 1.40%, an extraction rate of 13%, and 15g of coffee powder.

Substitute the formula: g of coffee liquid = extraction rate % * weight of coffee powder in g / concentration %, and you will get that the weight of the coffee liquid is 139g. Taking into account the water absorption rate of coffee powder which is almost twice, your final water amount should be set at 170g.