We all enjoy a good beer and lager! But if we leave it too long it will lose its flavour and taste stale and no one wants that. Any ale must retain its freshness until at least before the ‘best-before date’.
Loss of shelf-life in any product is a cause for concern for anybody involved in trying to ensure flavour and texture stability. It is still an issue even in this day and age with all the sophisticated methods available for controlling reactions in the packaging.
Preventing the development of off-flavour is one of those serious issues for a brewer because consumers judge a product like ale by its taste and flavour. If any ale has an issue it will produce brand rejection and loss of sales (Stephenson & Bamforth, 2002).
Much of the changes that occur in beer and lagers are similar to those experienced in other products especially beverages. It often pays to see if there are ways and means found in the storage of these products that can be applied to reducing staling in beer.
Sensory Testing of Beer
To understand how a beer will lose flavour, develop off-notes or go stale usually requires a trained sensory panel who can articulate and even quantify aged characteristics in ales and lagers.
A typical lexicon for a stale beer will be cardboard flavour, apple-like, wine-like, hay and straw aroma. These are all terms that have been employed to varying degrees when trying to characterise an aging brew.
The Flavour Of Beer
Ales are acknowledged to be some of the most delicate beverages of all. A vast amount of time and money is spent attempting to understand the complexity of beer flavour and how it changes with time. It is a process worth understanding because it has such a profound impact on our understanding of quality.
Over 1,000 different flavour compounds contribute to the myriad range of flavours in ale. Most of them are at concentrations below their respective sensory threshold levels. In total all of them contribute to some aspect of flavour but to varying degrees.
Beer is generally regarded as having poor stability compared to other beverages.
The two main factors according to Kamimura and Kaneda (1992) is oxidation and the other is contamination by contact with unsuitable materials, impurities and the ‘accidental introduction of harmful microorganisms’.
The chemical reactions that occur in say ale can also be found to some extent in other fermented products for example such as wine.
Compounds Contributing to Staling Notes
The fatty acid composition of the beer is the main contributor of flavour compounds as well as those associated with staleness and aging. Some in particular are critical and are specifically associated with the different descriptors mentioned earlier.
The formation of trans-2-nonenal is one of the main causes of beer staling. The main mechanism contributing to the generation of trans-2-nonenal in beer is the enzymatic or nonenzymatic oxidation of lipids and oxidized free fatty acids.
The enzyme lipoxygenase is the main culprit in catalysing the formation of trans-2-nonenal. It’s activity as well as the content of trans-2-nonenal in a beer before packaging is a useful measure of how badly an ale might age on storage (Drost et al., 1990).
Linoleic acid (C18:2) is a common fatty acid which is associated with the cardboard flavour of beer (Drost et al., 1971)
Reactions Occurring During Storage
Inside packaged beer, aldehydes might be produced de novo from intermediates of fatty acid oxidation, formed during the malting and brewing process or from Strecker degradation of amino acids present in the beer matrix (Baert et al., 2012).
Methods to Reduce Beer Aging
Sulphur dioxide has often been added to beer. The regulations on levels and how it is monitored are discussed elsewhere. It must be declared when levels demand it in the final product. Sulphur dioxide binds to certain functional groups on flavour molecules which dulls them from a flavour point of view. Whilst that might reduce or dampen down flavour impact it also means that those chemical groups that can go on for further reaction are taken out of the system. By that it means they will not contribute as much to beer staling.
Sulphur dioxide operates as a powerful antioxidant so it stops the formation of further free radicals which would normally go on to produce further reactions in beer that lead to staling.
Polyvinylpolypyrrolidone is sometimes added to remove polyphenols. It has very little effect on beer stability.
References
Baert, J. J., De Clippeleer, J., Hughes, P. S., De Cooman, L., Aerts, G. (2012) On the Origin of Free and Bound Staling Aldehydes in Beer. J. Agric. Food Chem. 60, pp. 11449–11472. (Article)
Drost, B.W., van Eerde, P., Hoekstra, S.F. & Strating, J. (1971) Proceedings of the European Brewery Convention, Estoril. pp. 451
Drost, B. W., Van den Berg, R., Freijee, F. J. M., Van der Velde, E. G., & Hollemans, M. (1990). Flavor stability. Journal of the American Society of Brewing Chemists, 48(4), 124-131 (Article)
Kamimura, M., & Kaneda, H. (1992). Off-flavors in beer. In: Developments in Food Science (Vol. 28, pp. 433-472). Elsevier.
Stephenson, W. H., & Bamforth, C. W. (2002). The impact of lightstruck and stale character in beers on their perceived quality: A consumer study. Journal of the Institute of Brewing, 108(4), pp. 406-409 (Article).
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