Hollander beater

[1] However, the wooden paddles and beating process of a stamp mill produced longer, more easily hydrated, and more fibrillated cellulose fibers; thus increasing the resulting paper's strength.

The Hollander used metal blades and a macerating action to separate the raw material, resulting in shorter cellulose fibers and weaker paper.

These contaminants often acted as catalysts for oxidation that have been implicated in browning of old paper called foxing.

Under power, the blades rotate to beat the fiber into a usable pulp slurry.

The objective of using a beater (rather than another process like grinding, as many wood-pulp mills do) is to create longer, hydrated, fibrillated fibers.