Discussion on the over extraction, under extraction and the extraction scheme of the coffee

Hello, this is Catch Mind as always whom want to play with the coffee. And today, I am going to discuss about the coffee brewing, under extraction and over extraction and how to design the extraction scheme of the coffee 

How does the coffee being extracted. 

Inside coffee, there are tons of substances that cannot even be pronounced, and 30% of them are potentially soluble. Just like the below drawing shows, when the coffee box contains 100 balls, 30 of them can directly be extracted.
In the box, when you bring out the balls, you can use the liquid called water. And this process is commonly called “extraction”.

Is it better to extract more substances from coffee? 

In Europe and US, when the coffee is extracted in a range between 18 to 22%, it is called “normally extracted coffee”. However, this range changes depending on the coffee’s condition. The coffee extracted in percentage out of the range can also create normal taste.

To make a good cup of coffee, you must take a look at other variables and bring out only the 15% of balls intentionally to be not considered as under extracted coffee. But if you were only able to take out fewer number of balls due to unexpected situations or take out too many balls, the taste and texture may be deteriorated. And such coffee is considered as under or over extracted coffee. 

How to define under extraction and over extraction of the coffee

This is judged by the number of balls you take out from the box, not by the amount of water or extracted water. Sometimes I met people who is confused, and they easily understands then we talk about the box and ball as metaphor. If you know coffee, box and balls, you can explain the logic behind the coffee extraction to anyone. 

But let’s be aware to not give “TMI” unintentionally.

Things to consider when thinking about the extraction scheme.

From now on I’ll give little “TMI” to discuss more important things,

In fact, this is the most important part. Maybe more related in setting up the coffee machine.

Coffee tend to have two distinctive characteristics depending on the condition and variables.

There are soft and tender coffee that is “very willing to be extracted just with a stream of water”

and though coffee that is more like “Try to extract me, I won’t even budge”.

For the former, you can easily get everything out from them but for the latter, it’s quite difficult. It takes more time and effort.
If you consider opposite method to these two different types of coffee, or take mediocre method, the extraction gets even harder.
In our world there’s such thing called white lies but in coffee world, lying does not works.
So, this is it. It was me giving out “TMI”. Now I am really going to talk about something more personal.

Designing extraction scheme for tough coffee

There are so many different tools and ways to bring out the balls out of the box, and this is called the extraction variable. From SCA, there are 20 different definition of such variables. If you are not going to bring the box upside down, the extraction process is never easy. So, I am going to share with you my personal story.

In the box shown below I put the factors that you can define at home or cafe without the extraction tools. 

The extraction process of the coffee is a team play of many different variables. Each variable does not apply individually in the extraction process. My teacher used to say, when one variable increases, the other variables tends to get smaller relatively. And this is called the concept of zero-sum.

So I take 4 variables that I think considerably significant in the extraction to build up the extraction scheme. As the drawing shows below, the extraction time and grind size is set up according to the coffee’s condition and degassing state, while other variables are remain fixed. (Increasing the box size of four variables and decreasing other boxes relatively)

After trying on the extraction like this, when the result is out of range, the head of water, turbulence, amount of coffee used and the extraction time is being adjusted. The grind size is not adjusted first because when you change the grind size prior to any other variables, the whole setting must be amended and it will take longer time. So, the grind size is not the first variable to be considered.

When the coffee is not extracted normally even after adjusting the brewing method represented by the water head and turbulence or extraction time, you must now change the grind size and the amount of coffee used like the orange box shown below. I have indicated the amount of coffee used as it may change according to the grind size.

Usually when it comes own to this level, you may be able to take out the number of balls close to the normal extraction. Science plays important role in many part of our life and coffee extraction is no exception to it. A good cup of coffee is made with “the science of a cup of coffee”.

Difficulties in brewing coffee (hand drip)

Maybe it is easier to extract coffee with a machine. Hand drip coffee involve lots of variables such as my technique in brewing the coffee. This takes lots of theory and practice.

If you use the machine, the setting fee substitute the variables involved around extraction process, and make the whole process much easier. That's why the machine's price changes according to the range and different it makes in the coffee extraction

So, how does over and under extracted coffee taste like,

The result must be judged by how a drinker taste and feel the coffee.

Taste and texture of under extracted coffee,

- Piercing and disturbing sourness

- Taste of raw glass and raw peanut

- Astringent taste like you ate under ripe persimmon

Taste and texture of over extracted coffee

- Dominant bitter taste, yet quite different from the bitter taste of dense coffee. It is still bitter when the density is low.

-  If severe, it taste like a medicine.

-  Rough texture, especially in your mouth and tongue. It may taste astringent.

Coffee is an acquired food thus, the taste may be defined differently according to drinker’s preference. Piercing sourness or disturbing bitterness may taste nice to some people. It is the drinker who has the right answer. However, the bad texture is a different thing. Anyone can feel the bad texture. Because between the texture and taste, there is a paper-thin boundary.

In conclusion...

Constructing a good extraction scheme is not only considered for brewing(hand-drip) coffee. The extraction tool varies from dripper to espresso machine that has 9 bar pressure.

My mum and her club members likes our neighborhood McDonald’s coffee very much. Out of curiosity, I went down to try their coffee. It was a little bitter but extracted to normal extraction and they were providing a good coffee regularly. My mum and her club members still go to that McDonald in our town to drink coffee.

Don’t you think you can make better coffee than a part timer in McDonald?

2019/03/22 - [행복한 커피] - The standard of the ideally extracted coffee

2019/04/08 - [행복한 커피] - Coffee Roasting Technique Tip 2. Density of green beans

2019/01/09 - [행복한 커피] - How to extract a perfect cup of coffee with your child.