How is beer stabilized in a brewery?

There are different pathways to analyze the stability of brewery products and promote long term shelf life. The final beer should be stable with: foam, flavour, non-biological haze, and microbiological haze (Bilge, 2015). Stabilization using gravity at cold temperatures is one of the most cost-effective and time-proven techniques for extending shelf life (Ockert, 2006). A required secondary closed fermentation consists of a period of 7-21 days after the krausen has fallen. Traditional lagering requires holding the beer for an extra 2-7 weeks for clarification and stabilization. Chilling the beer to between (-1)-3°C aids in settling the yeast and inhibits biological activity. The maltriose and dextrin content of the beer set the fermentation; if the post-krausen gravity is one-third of the original gravity, then the fermentation of high-dextrin beer should be at 1-5°C for fourteen days or more. When the beer gravity is less than one-third, then the fermentation of the low-dextrin beer should be at 1-3°C for under ten days before lagering (Noonan, 2003). Lagering allows for a more stable product from the combined effects of slower yeast metabolism, increased acidity, and lower temperatures. Additionally, tannins coagulate with haze-forming proteins, precipitating these and sulfurous compounds out of solution. Yeast cells do not decompose during lagering, they become more dormant as extract levels and glycogen reserves deplete; as the polysaccharides decline, yeast will reabsorb some esters and sulfur compounds. Downstream any oxygen introduced to the nearly-finished beer will cause the irreversible formation of diacetyl and oxidization of fusel alcohols and lipids. Determining the length of the lagering period comes from the malt; high-dextrin beers should be held at 1-2°C for 7-12 days each 2°Plato of original gravity, where low-dextrin beers should be held at 1-2°C for 3-7 days for each 2°Plato of original gravity (Noonan, 2003).

Since moderate diacetyl is a flaw in lagers, its reduction is one of the main goals of beer maturation. Diacetyl production comes from yeast's consumption of valine, and procedural condition alterations conditions that increase yeast growth or reduce valine uptake will produce increased diacetyl. The rate of spontaneous decarboxylation of α‐acetolactate to diacetyl dictates the rate of reducing diacetyl, while the yeast carries out the decomposition of diacetyl. Cold storage, limited oxygen and contemporary sanitary practices inhibit the formation of diacetyl (Krogerus and Gibson, 2013). Furthermore, adding bacteria-derived α-acetolactate decarboxylase to the beer at cellar temperatures, a period of 24 hours reduces diacetyl levels minimizing lagering periods (Godtfredsen and Ottesen, 1982).

The primary methods for non-biological stabilization are adsorption, precipitation, and enzymatic hydrolyzation (Bilge, 2015). Used in conjunction with cool ageing, the addition of finning improves head retention, clarity, and reduces maturation times. Finings such as gelatin and isinglass act by enveloping particles such as yeast cells, haze proteins, and tannins out of the beer. When a beer has reached terminal gravity, it is ready for fining. Finings perform better at colder temperatures; isinglass has a maximum utilization temperature of 16°C (Noonan, 2003). Wood chips can clarify cellar beer. Beech or hazelnut chips in the bottom of the lagering vessel will absorb moisture, polysaccharides will coat the chips, followed by yeast cells bonding as an agglomeration point and increasing beer clarity. Wood chips may be re-used with proper cleaning; yet, they add a significant amount of labour and are best implemented in horizontal vessels; resulting in infrequent use (Noonan, 2003).

While gravity settling is the most cost-effective method of stabilization, gravity is constant and settling difficult to speed up. Centripetal acceleration can replace gravity via a centrifuge. In the cellar, a disk centrifuge aids in removing yeast and other solids. Clarification by centrifuge can reduce the solids going to the filter which reduces the required filter material and their disposal costs (Ockert, 2006).

Process aids such as silica gels can absorb haze-proteins. Microscopic pores on silica gel house charged sites that bind haze-proteins while having a negatable effect on head retention. Hydrated silica gel gets added after primary filtration, as yeast decreases the effectiveness. Proper contact time may need a balance tank. Treatment with polyvinylpolypyrrolidone (PVPP) removes tannins, which acts like silica gel. PVPP reacts fast so it does not need the long resonance time. It is possible to regenerate PVPP, but the equipment required has a higher-capital cost. Filtration or settling can remove these stabilizing agents (Ockert, 2006). Composite products that combine silica gel and PVPP are available. The products lower filter differential pressure and allow for longer filtering runs than either product on their own (Bilge, 2015). An alternative method to prevent colloidal haze is to degrade the haze proteins so that they are not able to form a network with the polyphenols by using a peptidase such as Brewer’s Clarex at the start of fermentation, this allows lower oxygen exposure and uses with more limited filtration equipment (Van Zandycke, 2015).

The final stages before packaging involve removing any process aids and to perform a polishing filter step. A disk centrifuge removes most of the solids, a final filter removes products such as silica gel and PVPP and helps reduce cell counts of any live microorganisms. The most cost-effective beer clarification is achieved by powder filtration. Using materials such as kieselguhr or perlite as the process aid and can either be found in prefabricated sheets to use in plate and frame, lenticular or cartridge filters; or in loose powder applications such as leaf and candle filters. Rising concerns with powder handling with kieselguhr and respiratory diseases such as silicosis have made perlite and alternative technologies such as crossflow membrane filters utilized more often (Briggs et al., 2004). Heat treatments such as pasteurization always involve a risk of changing beer constituents. Increasing the microbiological stability of the product before pasteurization reduces the need for higher temperatures and holding times, it can also limit the amount of any heat-tolerant spore-forming contaminants (SPX Flow, 2013). The product must have the following criteria to be cold membrane filtered: good filterability, sterile utility connections, and high levels of Clean-In-Place for packaging equipment (Kunze, Manger and Pratt, 2010). 

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.