  The process of grinding coffee generates particles with high levels of
electrostatic charge, causing a number of detrimental effects including
clumping, particle dispersal, and spark discharge. At the brewing level,
electrostatic aggregation between particles affects liquid-solid accessibility,
leading to variable extraction quality. In this study, we quantify the
effectiveness of four charge mitigation strategies. Our data suggests that
adding small amounts of water to whole beans pre-grinding, or bombarding the
grounds with ions produced from a high-voltage ionizer, are capable of
de-electrifying the granular flows. While these techniques helped reduce
visible mess, only the static reduction through water inclusion was found to
impact the brewing parameters in espresso format coffee. There, wetting coffee
with less than 0.05 mL / g resulted in a marked shift in particle size
distribution, in part due to preventing clump formation and also liberating
fine particles from sticking to the grinder. With all other variables kept
constant, this shift resulted in at least 15% higher coffee concentration for
espresso extracts prepared from darker roasts. These findings pose financial
and sustainability implications, and encourage the widespread implementation of
water use to de-electrify coffee during grinding.
