Extraction in the context of coffee brewing, is the process of dissolving soluble solids and emulsifying aromatic oils in water. Coffee extraction is a precise process, and there are a few parameters that will determine the taste, aroma, and strength of the brewed coffee. Correctly brewing coffee requires using the correct amount of coffee grounds, extracted to the correct degree, (largely determined by the correct time), at the correct temperature.
Coffee is a liquid solution consisting of various substances found in the coffee bean dissolved in water. The extraction of these substances can be improved by increasing the solubility. Solubility can be increased by temperature, pressure, and agitation. Extraction can be tweaked by changing the grind size, and the extraction time.
For the espresso brewing method, coffee is extracted using pressure. The use of pressure means that the coffee can be extracted at a lower temperature, thus allowing more of the properties found in the bean to survive the brewing process and to be extracted into the cup. Extracting using high pressure as with espresso also allows the coffee properties to be extracted quicker. For this reason espresso coffee extraction takes between 20 and 30 seconds. Other methods that use pressure for extraction are the moka pot, percolator steam based espresso machines.
Filter coffee, on the other hand, is extracted just using heat and gravity. This means that coffee needs to be extracted at a higher temperature and for a longer period with the filter coffee brewing method.
Cold brew coffee extracts coffee properties from the coffee bean without any addition of heat. This means that the cold coffee brewing process takes between 12 and 24 hours for the coffee properties to be successfully extracted from the ground coffee.