Good Malt - Good Beer? How does malt influence the storage properties of beer? Malt is the soul of beer!
Beer has a tendency to develop chill hazes and permanent hazes during storage. Although malt quality plays an important role in this process, brewing technology has evolved to minimize its impact. Additions of cross-linking agents (such as formaldehyde) to mashes are still made in some developing countries, but such practices are outlawed in many parts of the world. More commonly, adsorbents are used at the beer filtration stage to remove haze precursors. For example, polyvinyl polypyrrolidone (PVPP) is used to remove polyphenols from beer. Silica hydrogels are used to remove proteins. Appropriate use of such materials can minimize the impact that `problem' malts have on final beer quality. In some parts of the world, proteolytic enzymes such as papain are still used to modify the proteins that lead to chill haze formation, thereby extending beer shelf life.
Ideally, we would have no need for such processing aids and additives; the quality of our raw materials and process would suffice to assure beer quality. Some beers are produced in this way. In such circumstances it is essential to focus on the soluble nitrogen content and profile of the malt, and on the polyphenol content and profile of both malt and hops.
Oxidative flavour stability
Recently, malt has taken much of the blame for the instability of beer flavour during storage. Is this warranted? At least some of the instability of the flavour of pale lager beers is due to unsaturated carbonyl compounds, the most infamous being trans-2-nonenal. One theory, which is widely subscribed to, suggests that this compound has its origins in oxidation of barley lipids. This may be catalysed by a specific enzyme (lipoxygenase 1) during the malting or mashing processes. Oxidation of unsaturated fatty acids (in particular linoleic acid) leads to formation of hydroperoxides, which then undergo further reactions, ultimately leading to volatile, highly flavour-active aldehydes, such as nonenal.
But the flavour stability story is not as simple as it first seems. Numerous studies have shown a relationship between many malt-associated parameters and beer flavour life. These include total nitrogen and free amino nitrogen. Heterocylic compounds from malt are also involved in beer staling, either directly via the Maillard reaction, or via yeast metabolism. And recently it has been shown that trans-2-nonenal can itself bind to beer proteins during production to be released during storage.