Coffee extraction describes the transfer of taste compounds from solid to liquid form and includes solubles and non solubles particles.
In solubles we find solids and gas that define the taste and the aroma of the coffee respectively.
In the non solubles we find solids and oils that combined characterize the body, the flavor and the aftertaste of the coffee.
Only 18-22% of the coffee bean is transferred to the cup and is translated in 1-1,5% of strength (acceptable concentration limits of solid coffee in 98,5-99% of water).
The extraction is the last part of the procedure, before that we have the pre-infusion and the increase of pressure (in espresso preparation).
During the extraction process, hot water comes in contact with the water molecules, removing the gas and soaking the solids.
The quantity of extraction is related to the rate of extraction and the contact time of hot water with ground coffee.
Factors that define coffee extraction
Extraction depends on the molecule size of ground coffee, the water temperature, the ratio of coffee to water and the stirring regarding drip coffee.
Factors that influence the rate of extraction
Factors that influence the rate of extraction are group temperature if it is about espresso and temperature of the brewing machine if it is about drip coffee. Other factors are the molecule size of ground coffee and the ratio of water to ground coffee.
Quality of preparation
The quality and the taste balance are defined by the extraction temperature of the solubles, the molecule size of coffee, the chemistry of water and the contact time. Moreover, the homogeneity of the extraction influences taste.
Water temperature and extraction
Water temperature influences the rate of extraction but also taste. There are compounds that dilute faster in higher temperatures and other in lower ones. This different alternation of solubles defines the balance of taste.
Bed and extraction
The shape of the bed is defined by the basket shape, influences the extraction and the upper layers of coffee are over-extracted resulting in a bitter and astringent taste while the lower layers are under-extracted.