How is Beer Stabilized in a Brewery?

Beer stabilization is essential for ensuring a long shelf life and maintaining critical qualities like foam retention, flavor, clarity, and microbial stability. There are several techniques brewers use to stabilize beer, and these can be categorized into biological and non-biological methods.

Cold Stabilization and Gravity Settling

One of the most cost-effective and time-proven methods for stabilizing beer is cold storage with gravity settling. By cooling the beer to temperatures between -1°C and 3°C, yeast and other solids settle naturally, reducing biological activity. This process, called lagering, is especially important in traditional lager production and can last anywhere from 2 to 7 weeks after primary fermentation (Ockert, 2006).

High-dextrin beers (those with higher residual sugar content) benefit from extended lagering, with typical holding times at 1-2°C for 7-12 days per 2°Plato of original gravity. Low-dextrin beers can be stabilized more quickly, needing 3-7 days per 2°Plato (Noonan, 2003). The cold temperatures help precipitate out tannins and haze-forming proteins, contributing to improved clarity and flavor stability.

Diacetyl Reduction and Yeast Reabsorption

Diacetyl, a by-product of yeast metabolism, can produce undesirable buttery flavors in beer, particularly in lagers. This compound is formed when yeast consumes valine during fermentation. While yeast naturally reabsorbs and breaks down diacetyl during maturation, the process can be slow, especially at colder temperatures (Krogerus and Gibson, 2013).

To speed up diacetyl reduction, some brewers add α-acetolactate decarboxylase, an enzyme that rapidly converts α-acetolactate to diacetyl, reducing diacetyl levels in as little as 24 hours and shortening the overall lagering period (Godtfredsen and Ottesen, 1982).

Non-Biological Stabilization Techniques

Non-biological stabilization focuses on preventing haze formation and improving the beer’s visual clarity. These techniques involve three key processes: adsorption, precipitation, and enzymatic hydrolysis.

• Adsorption: Finings such as gelatin or isinglass are commonly used to bind and remove particles like yeast cells, tannins, and haze proteins. These finings improve head retention, clarity, and reduce maturation times, performing best when beer has been chilled to colder temperatures. Wood chips like beech or hazelnut can also be used to naturally clarify beer by serving as agglomeration points for yeast and proteins (Noonan, 2003).

• Precipitation: Process aids such as silica gel and polyvinylpolypyrrolidone (PVPP) are added after primary filtration to remove haze-causing proteins and tannins. Silica gel works by adsorbing proteins, while PVPP binds tannins, both contributing to a clearer and more stable final product (Ockert, 2006). Composite products combining silica gel and PVPP provide even longer filtration runs and lower filter differential pressure.

• Enzymatic Hydrolysis: Enzymes such as Brewer’s Clarex degrade haze-forming proteins, preventing them from interacting with polyphenols. This method allows breweries to achieve colloidal stability with minimal filtration equipment and reduces oxygen exposure during fermentation (Van Zandycke, 2015).

Mechanical Filtration and Centrifugation

When traditional gravity settling is too slow or inefficient, breweries often turn to mechanical methods like centrifugation and filtration to clarify beer. A disk centrifuge in the cellar can rapidly remove yeast and other solids, reducing the solids load on subsequent filters and lowering filtration media costs (Ockert, 2006).

Powder filtration using kieselguhr or perlite is another common method, though there are concerns with kieselguhr due to the risk of silicosis. Perlite and crossflow membrane filtration are becoming more popular alternatives due to their safety and efficiency (Briggs et al., 2004).

Final Clarification and Packaging

Before beer is packaged, any added stabilization agents, such as silica gel or PVPP, must be removed. This is typically done with a final polishing filtration step, often combined with centrifugation. These processes not only enhance clarity but also help reduce the cell counts of live microorganisms, ensuring the beer remains microbiologically stable before it reaches consumers.

Cold membrane filtration is a modern alternative to pasteurization, offering a gentler approach to microbiological stabilization without the risk of altering the beer's flavor through heat. However, it requires the beer to be highly filterable and sterile utilities to be properly connected (SPX Flow, 2013).

References

Bilge, D. (2015). Beer Stability and Stabilization.

Briggs, D., Brookes, P., Stevens, R. and Boulton, C. (2004). Brewing, Science and Practice. Cambridge: Woodhead Pub., pp.541-588.

Godtfredsen, S. and Ottesen, M. (1982). Maturation of beer with α-acetolactate decarboxylase. Carlsberg Research Communications, 47(2), pp.93-102.

Krogerus, K. and Gibson, B. (2013). 125^th Anniversary Review: Diacetyl and its control during brewery fermentation. Journal of the Institute of Brewing, pp.86-97.

Kunze, W., Manger, H. and Pratt, S. (2010). Technology Brewing & Malting. 5th ed. Berlin: VLB, pp.481-526.

Noonan, G. (2003). New Brewing Lager Beer. Boulder, Colo.: Brewers Publications, pp.191-201.

Ockert, K. (2006). Fermentation, cellaring, and packaging operations. St. Paul, MN: Master Brewers Association of the Americas, pp.135-160.

SPX Flow, (2013). Removal of Bacteria and Spores from Milk, Using Membrane Filtration. [online] Available at: https://www.spxflow.com/en/assets/pdf/APV_Bacteria_Removal_in_Milk_ESL_22011_04_08_2013_GB_tcm11-7661.pdf [Accessed 10 Feb. 2019].

Van Zandycke, S. (2015). Clear Beer Made Easy and Other Benefits of Using Brewers Clarex in Beer. MBAA Technical Quarterly, 52(3), pp.141-145.