STiR coffee and tea 59
Extraction has its limits
So far, this concept seems straightforward: Increase
the surface area of the coffee exposed to the water
= increased extraction; however, there is a prob-
lem. Every brewing methodology has its target for
how much area should be exposed, and it is critical
that there is not an over-extraction of soluble solids
from the coffee, which would be just as detrimental
as an under-extraction of the soluble solids.
The graphic (at right) depicts the concept.
This empirical illustration illustrates that there
is a lower and upper limit to the desired extrac-
tion, with too little extraction resulting in a weak,
underdeveloped brew and too much extraction
resulting in a bitter, off-tasting result.
The next goal is to optimize the mean, or av-
erage particle size of the ground coffee precisely
to the desired exposed surface area, given the
brewing methodology. Also, to make things more
difficult, it is critical to optimize the mean particle
size for the brewing method, as well as optimize
the percentage of particles in the desired particle
distribution range(s).
The graph at right shows the difference be-
tween a standard filter brew, K-Cup, and espres-
so grind. It is important to note the "bump" on
the espresso grind profile, which is desired for
the unique "bricks and mortar" grind profile of
an espresso product.
