Effect of carbon dioxide in coffee beans on coffee extraction

The reason why there is a range of gold extraction rate in coffee extraction (keeping the coffee extraction rate between 18% and 22%, the probability of being delicious is the greatest). The most fundamental reason is that the sour, sweet and bitter flavor substances in coffee will be taken away by water because of their molecular weight and polarity.

In other words, in the whole extraction process, the sour substances and aroma components with small molecular weight and strong polarity are the first to be extracted, followed by sweet substances with medium molecular weight and weak polarity, and finally bitter substances with large molecular weight and non-polarity.

The figure above shows an extraction process with the increase of extraction rate, and the degree to which various components are extracted can be seen. When the extraction rate of coffee is 18%-22%, the sweet and sour taste of coffee can often be balanced.

And controlling this process is the process of making coffee, and the factors that affect this process are the thickness of the grinding degree (default is the same coffee bean, the same meteorological environment), the temperature of the water, the mechanical energy of the water (including water pressure, the stirring of the current, the height of water injection, etc.), time, etc., and we can regard all factors other than time as energy. If we want to spread these particles in coffee into the water, we need energy to do work on them or increase the contact time between coffee powder and water.

In fact, the smallest molecular weight in coffee is almost carbon dioxide (there are a small amount of small molecular weight volatile acids, aldehydes, aliphatic hydrocarbons, etc., which may be smaller than carbon dioxide). According to the above theory, in the process of extracting coffee, carbon dioxide should be the first to be dissolved by water, but in an instant it precipitates again and dissipates into the surrounding air in the form of gas. In other words, assuming that the shorter the roasting date of the coffee bean is, the more carbon dioxide remains, we need to use more energy to extract the coffee, or let the coffee powder come into contact with water for longer.