How much caffeine is extracted from roasted ground coffee beans?

Question

What is the percentage of caffeine extraction when brewing coffee? In other words, how much of the caffeine in ground coffee dissolves in hot water? Is it correct that the degree of extraction is between 90% and almost 100% with whatever brewing method?

The different brewing methods were unequally efficient at releasing the caffeine from the coffee beans. Even our champion, the ristretto, only managed to release about 31 percent of the original caffeine. On average, all the techniques only release about 10 percent.
— How Much Caffeine Is Really in Your Coffee?

… caffeine levels can vary significantly but its been estimated that 90% of the caffeine is extracted within the first minute of brewing. The variance in caffeine levels is attributed to several factors including extraction time, temperature, grind level and type of coffee used - making true calculations difficult to publish.
— Caffeine in Coffee

Answer 1

I believe the confusion arises from what is extracted.

Normally, a sane person would like to extract the tasty aromatic oils out of the bean and dissolve them in the water to be able to enjoy it. Apparently, the effect of dissolved caffeine to the taste of the coffee is practically non-existent.

Two facts:

• It is difficult to extract all of the oils. Moreover, you probably do not want them all. You just want to extract the most delicious part^*.
• It is quite easy to extract caffeine just by leaving the beans in water even in a very short amount of time⁺.

Therefore, most of the caffeine dissolves in the water way early before any of the delicious oils dissolve. I have never had any measurement by myself but it is said that

• around 90% of caffeine is extracted even in a few seconds.
• around 15% of oils are extracted in a typical cup.

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^{* For example, over-brewed coffee tasted bitter. Most granule coffees are bitter, too. As they are prepared by extracting nearly everything out of the beans with huge percolators, then drying the extracted syrup out.}

^{+ This is actually how Swiss de-caffeination method works. You just leave the green beans in water for some time. Caffeine dissolves in water. You take the beans out of water and dry them.}