There is an overall tendency for the molecules in a mixture to migrate from areas of higher concentration towards areas of lower concentration via a process known as diffusion.
Molecules diffuse faster at higher temperatures. In a cold environment, each molecule has less kinetic energy and therefore can’t diffuse as quickly.
Higher temperatures increases the possibility of extracting compounds from the coffee bed whilst also migrating out fines and emulsifying coffee oils into suspension
There is a law in physics called the no slip boundary condition which states that the velocity of a liquid flowing past a surface is exactly zero at the surface itself. In other words, particles of fluid will adhere to the walls (or boundary) of a solid.
Unless there is a turbulent flow, the NSBC means that extraction relies on diffusion which is a slow process.
Methods involving more turbulence, such as ibrik or syphon, usually require shorter time frames for the extraction process.
Further away from the particle surface in a slurry of coffee grinds and water, if the fluid is moving, the flavour molecules can be carried away by the movement of the liquid, a process called advection.
When a coffee bean breaks under the forces involved in grinding, some large fragments (boulders) and some small fragments (fines) are produced.
Cutting is expected to cleave through beans without producing many fines; most of the fines productiontakes place when beans are shattered between grinder burrs.
At higher temperatures, the kinetic energy of water molecules is increased. This raises the rate of extraction by giving each water molecule higher mobility, which increases the possibility of leaching out compounds from the coffee bed whilst also migrating out fines and emulsifying coffee oils into suspension
We recommend that immersion brew methods should be prepared with grind sizes much finer than what is traditionally recommended.
But grinding too fine with immersion brews can result in excessively turbidity.