Greetings!

Hi everyone! I’m Reika from the roasting team and this is my first post of the blog series on coffee extraction theory. 

It’s been 3 months since I joined Kurasu and I am building up my knowledge on coffee step by step, day by day.Whenever I have a question, I don't just google the answer - I actually form a hypothesis and test it to gain better understanding. 

So through the blog posts, I’d like to share with you test results and extraction theories to help you create a brewing recipe off the top of your head. Currently, I am experimenting with various topics on coffee grounds and water, so stay tuned!Let’s explore ways to make our home brew extra delicious and special together. 

Grind Size and Flavours 

Moving on to today’s topic - “Grind Size.”

The first thing that comes to my mind when I think about adjusting flavour is experimenting with grind size. 

How do you decide on your grind size? What kind of  information on the packaging do you check for?

How does grind size affect the flavour of coffee?

To explore this question, I have brewed multiple cups of coffee from fine to coarse grind and rated flavours on a scale of 5. 

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<Equipments>

Dripper: Hario V60

Recipe: Kurasu recipe for Hario V60 

Grinder: EK43

Coffee: Peru (light roast)

<Scale>

Grind size #5 Fine ----------------　#11 Coarse

Flavour 1 Weak ---------------- 5 Strong 

<Results>

Flavour ／ Size	#5	#6	#8	#8.5	#10	#11
Acidity	0	1	3	5	4	1
Sweetness	1	1	4	5	3	0
Body	0	5	4	3	2	0
After taste	0	1	4	5	2	0

 

<Comments>

#8.5 (ideal) - The acidity of the coffee beans came through clearly and it was in harmony with sweetness, while also having a  pleasant lingering aftertaste. 

#5 (too fine) - Brought out  various unpleasant tastes and neither acidity nor sweetness was extracted. 

#6 (slightly fine) - Produced little acidity and sweetness with lingering various unpleasant tastes and bitterness.

#10 (slightly coarse) - Produced acidity and sweetness but lacked in body with abrupt end to aftertaste.

#11 (too coarse)  - A hint of acidity came through but overall bland with very few flavours. 

* * *

Now I will explain the flavors in more depth, showing breakdowns of extraction with the amount of water poured. 

#5 (too fine) : Extraction time 3’07

#8.5 (ideal) : Extraction time 2’10

#11 (too coarse) : Extraction time 1’58

First of all, flavours of coffee are extracted in the following order:acidity, sweetness, aftertaste and unpleasant taste/bitterness.

This is in the order of  solubility. Concentrated flavours of acidity dissolve into water quickly. 

Sweetness is also relatively soluble and comes through after acidity. 

The delicious flavours of coffee consists mainly of acidity and sweetness.

However, note that #8.5 also includes “aftertaste” and the key to good and ideal coffee isto complete the brewing process at the extraction stage of the pleasant aftertaste.  

Over and Under Extraction

If the grind size is too fine, extraction speed becomes too fast and all of the good essence runs out in the first half of the extraction process, resulting in unpleasant tastes and bitterness to be extracted in the second half like in #5. 

With this in mind, let’s dig into over and under extraction.

If you feel bitterness and unpleasant aftertaste lingering for long, your coffee has been over-extracted. On the other hand, if the grind size is too coarse and extraction is slow and insufficient, your coffee will be under-extracted. This under-extraction results in weak and bland coffee with only a hint of acidity that dissolves at the beginning. Sweetness will not be extracted and once coffee is swallowed, flavours instantly disappear to leave with you an abrupt finish. Even if you use the same brewing recipe, your coffee would taste completely different depending on grind size. 

Summary: adjust grind size to extract the perfect balance of flavours and aftertaste.

A good cup of coffee consists of balanced flavours of acidity, sweetness and aftertaste. 

Experiment with grind size to avoid extracting unpleasant taste or ending up with weak coffee. Keep trying until you reach the ideal harmony of flavours!

* * *

Next topic is the ratio of coffee beans to water. 

How does the taste of coffee change with the amount of coffee beans you use? How do we decide on the most suitable ratio? Find out in my next blog post!