The fifth part of the golden cup theory of coffee: the formula for calculating the extraction rate of coffee by immersion brewing.

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In the non-espresso coffee world, we have about two types of brewing:

Trickle filter (drip method): as commonly known as hand flushing, American coffee maker and so on.

Immersion (infusion-immersion method): such as Syphon, French pressure, Philharmonic pressure (AeroPress), smart filter cup and so on.

Many people will find that the amount of powder using Syphon is more than that of hand-flushing, so if we use the hand-flushing extraction rate method introduced last time, we will find that it seems to be insufficient extraction. Then when we reduce the amount of powder to find a way to "extract correctly", we will find that the coffee does not seem to taste that good. The reason is very simple, that is, the way to calculate the extraction rate by "immersion method" and "drip filtration method" is different! Why? This is the mystery we are going to solve today.

In drip filtration, the formula we use looks reasonable (in fact, it is also reasonable in drip filtration) is as follows:

Extraction rate = weight of finished coffee x TDS (that is, the amount of coffee extracted) / coffee powder consumption

We have a relationship:

The final brew of coffee

< 冲煮实际用水   那水跑到哪里去了呢? 最主要的就是被咖啡粉吸住了。这个吸住的水多少其实以后会是一个重要的课题, 不过我们暂时不理它, 就知道有一些水被吸住就是。在滴滤式的冲泡法中, 后面被吸住的咖啡, 基本上再用力冲出来我们也不要了, 所以在算萃取率时我们不用理会它。   但是在用 Syphon, 法国压, 爱乐压, 聪明滤杯时, 这些被吸住的咖啡, 浓度、品质差不多就是出来的咖啡! 事实上它是正确萃取的咖啡, 只是进不去我们的杯子里。我们在算萃取率时如果没有考虑进去, 就会以为我们萃取率过低! 这就好像说有个工厂做出 10 个很完美的产品, 在运送过程中失去 2 个, 所以只有 8 个真正上市。但我们不能说这间工厂只做到 80%, 要检讨也只能检讨运送过程。   所以呢, 我们在算浸泡法型的冲煮, 要用另一个、事实上更简单的公式 (简化版), 那就是:  

[example]

Let's take an example of 2004 WBC champion Tim Wendelboe using AeroPress: he used 14g of coffee powder, 215g of water, and TDS measured 1.38%.

Using our "new" formula, we can calculate

Extraction rate = 215x 0.0138 / 14 = 21.19%

But our WBC champion uses MojoToGo (an iPhone App from VST) to calculate 18.69%. Why is that? The reason is very simple, this is using our "old" formula, maybe the MojoToGo at that time did not consider the different extraction rate (the current one has been changed). Let's do the math. Although Tim Wendelboe does not show the weight of the finished coffee after brewing, we can calculate (and should also be MojoToGo's) that the finished coffee is:

189.62g

We will show you how to get this magic number later. Then using the "old formula" accordingly, it will be calculated.

"Old" extraction rate = 189.62 x 0.0138 / 14 = 18.69%

It is the film that shows the extraction rate of the old algorithm, so we can find that there is really a considerable gap! In fact, we are actually talking about a "simplified version" of the algorithm, let's now come to a more accurate algorithm. Here we are going to discuss the "water absorption" of coffee, that is, after the coffee is brewed, how much water is absorbed by the coffee and does not enter our last cup of coffee.

Water absorption is often explained by how much water 1g powder can absorb. For example, generally speaking, the water absorption rate is 2, that is, 1g powder will absorb 2g of water. So our 14g coffee powder will suck.

14 x 2 = 28

That's 28g of water. We assume that the 189.62g coffee brewed is basically the same concentration as the 28g water that did not enter our cup of coffee, so it is extracted altogether.

(28 + 189.62) x 0.0138 / 14 = 0.2145

That is, the extraction rate of 21.45%, our simplified version is still relatively close to this. In a word, the calculation methods of extraction rate of dripping method and immersion method are different. The exact formula of the immersion method is as follows: