All tea is graded by the size of the final leaves and starts with the fermentation process. To start the fermentation process the tea leave is generally broken and twisted breaking the leave into smaller particles. After the fermentation and drying processes the tea leave is passed through various shaking sieves that separates the larger and smaller levels of leaves. The choice teas are of the larger particle size and considered of a higher grade. The smallest particles are tea dust (called fannings or fines) and should never be mixed with the larger particles. This is because during infusion (steeping) the leaves of different sizes take different amounts of time to release their taste. Thus, small tea dust is over extracted and the larger tea particles are under extracted.