The shelf life of beer depends on its rate of oxidative staling and
its antioxidant capacity.
Oxidative staling occurs as a result of free radical oxidation. Free radicals are atoms, molecules or ions that have an unpaired electron, which makes them unstable and highly reactive because they seek out and steal electrons (oxidation) from nearby molecules, which causes damage and premature aging.
While beer is being stored, molecular oxygen inside it is converted to “reactive oxygen species” (ROS) free radicals by trace metals such as iron. When a free radical stabilizes itself by taking an electron from a neighbor, that neighbor also becomes a free radical and, in turn, steals an electron from another neighbor. In this way, a “free radical cascade” is triggered, a perpetuating chain reaction that results in the production of aldehydes and ketones. These are the compounds in beer that give it its stale flavor.
For example, one of the aldehydes that causes the “cardboard-like” flavor of stale beer is trans-2-nonenal. This has a typical carbon flavor, which doesn’t make the beer very fresh or sessionable and deters people from drinking it, since it is very bitter.
The main problem when it comes to optimizing a beer’s shelf life is that the majority of manufacturers can only perform shelf life testing on packaged beer, which makes it impossible to determine which steps in the beer making process have had a positive or negative impact.
Head of Flavor Stability at FlavorActiV, Heidi Grimmer, recently talked about how Bruker BioSpin’s e-scan electron paramagnetic resonance spectroscopy (EPR) systems enable each manufacturing step to be analysed in order to find out which beer processing steps could be changed to improve shelf life.
FlavorActiV is the global leader in the supply of Good Manufacturing Practice (GMP) standards, training panels and proficiency in quality control environments. Grimmer explains that it’s important to be able to link some of the tasting to an analytical method, particularly because a lot of the tasting can’t happen in process, but only in packaged beer.
What the Bruker systems do is measure the rate of free radical formation in the beer, which tells the brewer about its shelf life. Basically, the faster the rate of radical formation in the beer, the more quickly the beer ages.
Initially, antioxidants present in the beer quench free radicals before they can be captured. Antioxidants are molecules that keep free radicals in check because they can donate an electron without becoming unstabilized, thereby stopping the free radical cascade or chain reaction in its tracks. This quenching creates a “lag” in the time profile of EPR signal intensity and this lag directly reflects the beer’s antioxidant content.
Bruker’s EPR Lagtime Analyzer is a compact, easy-to-use bench-top device that serves as a powerful tool for directly measuring the antioxidant capacity of the beer. Brewers can perform a lag time assay to check the impact of various manufacturing steps on the beer’s final antioxidant content. The technology enables measurement of anything from brewing, to malting, all the way through to wort cooling, fermentation and maturation.
With EPR, you can go all the way through the process, right up to the packaging and it provides a very good fingerprint of the beer freshness throughout, says Grimmer: “At each point, you then identify those steps that either impact positively or negatively on the brewing process, and hence you are then able to measure how that improves your beer freshness and enjoyment for the consumer.” The next step, she continues, is to then try to optimize the raw materials and the brewing process, such that the antioxidants in the beer are optimized. This can reduce the rate of radical formation in the beer and hence increase the shelf life.
Generally, breweries use sensory analysis (beer tasting) to assess the staleness of beer, but this is not always practical for assessing process changes. Furthermore, it can take weeks or months to perform and it is also confounded by subjectivity.
With EPR, brewers can combine the lag time assay with sensory feedback to provide a two-way approach to ensuring beer freshness.
Grimmer says the important thing is to identify and then to fix: “It’s about finding the critical points in your process that you then measure in your packaging. Critical points such as increasing the fermentation rate or increasing the dissolved oxygen, and then answering the question ‘how does that impact on the beer?’ “
It’s about identifying and making sure that once you have measured the method, what gets fixed stays fixed, she concludes.