Finings are processing aids added to unfiltered beer to remove yeast and protein haze. During fermentation yeast cells and beer proteins largely derived from the malt form a colloidal suspension that appears as a haze. A colloidal suspension forms when very small, charged particles are suspended in a liquid. An electrostatic charge, known as a zeta potential, repels one particle from the next and serves to impede the settlement of the solid particles from the liquid phase.
In beer styles originating in the British Isles this turbidity was traditionally removed by the addition of a solution of a charged polymer solution. Examples include isinglass, gelatin, and gum arabic solutions. In unclarified beer, yeast cell walls carry a negative charge. Isinglass and gelatin solutions are proteins that carry a positive charge. When added to newly fermented beer, the charged finings interact with the yeast and neutralize the zeta potential present on the cell wall. This eliminates the repulsive forces and sticks the yeast cells together to form a larger particle called a floc. These larger particles settle considerably faster than they would otherwise, as dictated by Stokes’ law.
The neutralization happens quickly and the use of finings can be remarkably efficient, so much so that it enabled British brewers to present fresh, unfiltered, cask-conditioned beer with a pleasing clarity without the need for filtration or extensive settling time. Some brewers will use finings to reduce the yeast suspended in beer before preparing a beer for filtration.
Preparations intended to precipitate proteins rather than yeast are referred to as auxiliary finings. Often derived from carrageenans or alginates, these preparations carry strong negative charges that attract and form flocs with positively charged proteins. Although yeast finings such as isinglass can be used in conjunction with auxiliary finings, they cannot be added at the same time because each would neutralize the other, rendering both fining agents ineffective.