6- Contact time:
It’s the time the brewing water stays in contact with the ground coffee. It’s the time spent to brew the coffee. Extraction is proportional to contact time so more contact time means producing greater extraction of solutes.
This happens because the solvent molecules can either interact with sites or solvent molecules for which they wouldn’t otherwise have time. It could reach a point where no additional extraction would be produced.
Longer contact times will increase intensity of body, coffee flavor, bitterness, and sourness. With short contact times the coffee would be under extracted (weak, flat.. etc). There are a range of molecules we want extracted. Under or over extracting produce unfavorable cups.
Therefore, as is the case with the other extraction parameters we need to be in the acceptable range. Contact time will vary depending on the grind size, and filtration method.