Why is it recommended to grate only the amount of real wasabi rhizome intended for immediate consumption to maximize its potency?

Because the enzyme myrosinase begins degrading immediately upon grating, causing the therapeutic compounds to dissipate rapidly.

The health benefits of freshly grated wasabi are directly tied to the immediate chemical reaction that occurs during grating, specifically when the enzyme myrosinase interacts with glucosinolate to form active ITCs. This reaction and the resulting ITCs are highly volatile. Upon exposure to air following grating, the myrosinase enzyme begins to degrade rapidly, leading to the quick dissipation of the therapeutic ITCs. Therefore, for maximum effect, the root must be consumed almost immediately after the grating process is complete, as the chemical structure responsible for the potency breaks down quickly over time.