Lesson 2 - Warm and Cold Maturation
This lesson explores the processes of warm maturation and cold maturation. Warm maturation can also be described as flavour maturation This process removes negative or unwanted flavours from the beer post-fermentation. Cold maturation occurs at lower temperatures (below 0°C), which in turn causes haze-forming components to form. These components can then be removed by precipitation or clarification via centrifuge or filtration. This lesson highlights the importance of these processes, how they affect the quality of the final product, and how we manage these maturation steps.
Cold Maturation
The main reason why we use cold maturation is to form and ultimately remove haze forming components, to ensure long term colloidal stability, e.g. to lower the risk of haze formation during a beer’s shelf-life.
A number of beer styles (and consumers) demand that the beer must not contain any haze throughout its shelf-life. The brewer must thus remove all haze forming materials to avoid a non-biological haze.
The Haze lesson in the Beer Properties unit goes into significant detail about the types, formation, and measurement of haze in beer. The Processing Aids and Additions lesson details the mechanisms of how various process aids help to form and remove these haze complexes. We are discussing non-biological haze here to provide a high-level explanation as to why we use cold maturation.
The articles below provide a brief overview of the formation and measurement of colloidal stability:
Haze is most commonly caused by the formation of protein and polyphenol complexes. Beer contains acidic proteins and numerous polyphenols that form loose hydrogen bonds when they come together. The polyphenols can further polymerise and oxidise to form tannoids. When tannoids bond with numerous proteins, they can create a reversible chill haze. The haze forms around at 0°C but then re-dissolves at around 20°C. If the beer is cooled again, there is a risk of stronger bonds forming, resulting in an irreversible permanent haze.
Because of this, the brewer must ensure that the haze is formed in the brewery and not in the consumer’s beer fridge, hence the need for cold maturation. By chilling the beer to -1 to -2°C for 3-7 days, these protein-polyphenol haze complexes (often referred to as a chill haze) are formed. Once formed, the haze particles can then be removed by precipitation (described by Stokes’ Law) or by centrifugation/filtration.
The beer must not be allowed to reach above freezing until the haze particles have been removed from the beer, otherwise these complexes will break apart and remain in the beer.