Lesson 6 - Process Aids and Additions

Tannic acid is a class of polyphenol derived from gall nuts. Gallotannin is a commercial form that is used in breweries. Gallotannin adsorbs and precipitates haze forming protein from the beer.

Tannic acid is negatively charged and interacts with positively charged areas of sensitive (haze forming) protein. This forms an insoluble complex that precipitates out of the beer, as modelled by Stokes’ Law. There are a number of advantages of tannic acid:

• It is supplied in granulated powder form, creating no dust during handling.

• It does not interact with foam positive proteins and thus has no impact on foam stability.

• It reacts instantly with proteins, so does not require an extended contact time.

• As tannic acid is a form of polyphenol, it improves shelf-life by increasing the beer’s natural antioxidant potential (polyphenol content).

• It has no impact on flavour or mouthfeel.

• It has a positive impact on flavour stability by complexing with metal ions that catalyse aldehyde formation, such as iron and aluminium, which leads to staling of the beer. Reducing the metal content can slow the beer’s ageing process. These metal ions are quickly co-precipitated with the gallotannin-protein complex and removed during centrifugation or filtration.

Tannic acid is prepared by mixing it with deaerated water to form a slurry. We can add it to the beer during transfer to maturation or pre-filter; it is typically used at a dosing rate of 2-8 g/hL, Pre-maturation addition results in the formation of voluminous or fluffy precipitate, otherwise known as tank bottoms. This beer should be centrifuged pre-filter to remove the tank bottoms, which contain a high concentration of solid particles. These solids could otherwise block the filter pores and shorten filter runs.

New preparations are now available for pre-filter addition that have a short contact time. They can be removed easily by filtration without negatively affecting filter run lengths. They can also be used in conjunction with other stabilisation aids such as PVPP.