A solvent (from the Latin solvō, “I loosen, untie, I solve”) is a substance that dissolves a solute (a chemically different liquid, solid or gas), resulting in a solution. A solvent is usually a liquid but can also be a solid or a gas. The maximum quantity of solute that can dissolve in a specific volume of solvent varies with temperature.
In coffee brewing, the solvent is the water. Water dissolves soluble particles in the solute, which is the coffee bean, and the result is the coffee drink.
How the conditions concerning the solvent are manipulated determine the type of coffee extraction that is achieved.
The main factors concerning the solvent that can be adjusted are temperature, volume and time. If any one of these factors are adjusted, the coffee extraction will be different.
For example, more of the solvent (water) will result in a weaker overall extraction. If the solvent is heated to a higher temperature, more properties of the solute are extracted. Finally, if the solvent is in contact with the solute for a longer period of time, more of the properties will be extracted.
Grinding coffee beans finer also increases extraction as grinding finer increases the surface area that is in contact with the solvent.