Oxidation in brewing is a critical factor that can impact the final beer's quality, flavour, aroma, and stability. When oxygen interacts with various compounds in the wort or finished beer, it initiates chemical reactions that can lead to undesirable flavours and aromas, loss of freshness, and a shorter shelf life.
The shelf life of beer is affected by two parameters: dissolved oxygen present in the bottle and off-flavour precursors already present in the beer. Oxidation reactions continue during storage, especially if any residual oxygen remains in the packaging, gradually breaking down compounds that contribute to the beer's freshness. Oxygen that remains in the beer after packaging (often referred to as dissolved oxygen or headspace oxygen) is a primary driver of oxidation. Even trace amounts of oxygen can lead to the formation of off-flavours.
Oxidation processes in brewing can be broadly categorized based on causes (the source of oxidation) or processes (the mechanisms of oxidation).
During mashing, the high temperature and agitation create an ideal environment for biochemical reactions to happen very fast. At 55°C (131°F), lipoxygenase enzymes (LOX 1 and LOX 2) from the malt interact with oxygen to break down lipids, producing trans-2-nonenal, a compound responsible for the undesirable "cardboard" flavour often associated with stale beer.
LOX enzymes are iron-containing enzymes that catalyze the oxidation of polyunsaturated fatty acids, primarily linoleic acid in malted barley.
Auto-oxidation is a non-enzymatic process where oxygen interacts with unsaturated lipids and flavour compounds in wort. Trans-2-nonenal is also formed via auto-oxidation of linoleic acid through a free radical chain reaction, contributing around 50% of trans-2-nonenal production, with the other 50% coming from LOX.
Beyond lipid oxidation, polyphenol oxidation also impacts flavour stability. Here, oxygen interacts with polyphenols (e.g., tannins, flavonoids), which can then react with proteins, forming haze and contributing to staling. This pathway causes bitterness, astringency, and haze, reducing clarity and flavour stability in beer.
There are two main ways to improve flavour stability. The first way is to limit the interaction between the raw material and the external environment within the brewery, reducing contact between oxygen and raw materials is a critical factor in minimising oxidation in brewing, but it is typically not sufficient on its own to fully prevent oxidation. Even with reduced external exposure, raw materials, such as malt, contain compounds that are susceptible to generating oxidised compounds. They can undergo internal enzyme-induced oxidative reactions, leading to flavour degradation over time.
While using a closed system helps to reduce oxidation, it is almost impossible to eliminate all oxygen exposure during production and packaging. Therefore, stabilizing agents are often necessary to capture any residual oxidative elements.
The second way to improve flavour stability is to control the process, in two approaches. Selecting the best possible raw materials and using antioxidants. By doing so, the expression of off-flavour compounds is neutralised and delayed.
ANTIOXIN® SBT is a blend of antioxidants. Each component—Vitamin C (ascorbic acid), metabisulfites, and selected tannins (gallotannins)—plays a unique role in preventing oxidative damage. Here’s a breakdown of how each component works to protect beer from oxidation, along with their mechanisms of action.
By combining these antioxidants, ANTIOXIN® SBT provides a multi-faceted approach to oxidation protection, targeting free radicals, dissolved oxygen, and catalytic metals that contribute to flavour degradation and staling providing full protection Each component works in synergy to maintain the freshness and flavour stability of beer throughout its shelf life, from brewhouse to consumer.
AEB conducted a study, with a brewhouse of 500 hl per brew evaluating two sets of six brews. ANTIOXIN® SBT was added in a dosage of 5 kg/batch equivalent to 10 g/hl of hot wort.
An Indicator Time Test (ITT) test was conducted to monitor oxidative stability with the variable being the presence and absence of ANTIOXIN® SBT additive. The test involves observing the decolourization of DCPIP (2,6-dichloroindophenol) a chemical indicator used to assess oxidative stability. It’s initially dark blue when in its oxidized form. When it encounters a reducing environment (an environment with antioxidant capacity), it loses colour and becomes colourless as it gets reduced.
QUICK DECOLORIZATION (HIGH STABILITY): In a fresh or protected beer with high antioxidant capacity, DCPIP decolorizes rapidly to a clear, colourless state. This indicates that the beer has a strong ability to reduce oxidizing agents, meaning it is less prone to oxidation and staling. The beer’s freshness helps it quickly neutralize DCPIP, preserving its pale or natural colour.
SLOW/INCOMPLETE DECOLORIZATION (LOW STABILITY): In an oxidized or less stable beer, DCPIP decolourization is slow, and it may retain some of its blue or red hues by the end of the test. This suggests that the beer has limited antioxidative capacity and is already partially oxidized. As a result, it struggles to reduce DC
Protected Beer (Pale/Golden Color): A fresh, stable beer sample that effectively reduces DCPIP will retain a pale or golden colour, with no residual colour from the DCPIP. This appearance reflects good oxidative stability, as the antioxidants in the beer have neutralized the indicator quickly.
Oxidized Beer (Reddish or Darker Color): In a beer that has already undergone some oxidation, you may observe a red, amber, or even pinkish tint. This is partly due to the slow reduction of DCPIP, which leaves residual colour. Additionally, oxidation in the beer itself can darken its colour over time, leading to a reddish or amber hue that signals to stale.
The colour change from dark blue to colourless can be measured using a spectrophotometer, allowing for an objective assessment of the sample's redox potential.
All samples without ANTIOXIN® SBT have a similar curve, confirming that the test results are consistent and reliable.
Samples with ANTIOXIN® SBT show slower decolourization, indicating that ANTIOXIN® SBT is effective in slowing down oxidation.
AEB conducted a quantification study to assess the effectiveness of ANTIOXIN® SBT in reducing aging and off-flavor compounds. The analysis was performed using Gas Chromatography (GC).
ANTIOXIN® SBT substantially lowered aging compounds, helping to prevent stale or aged flavours and demonstrating its effectiveness in prolonging beer shelf life by reducing specific oxidative compounds.
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Ana Victoria Vasquez de la Peña
ana@neumaker.com.au
8 November 2024
References:
AEB Group. (n.d.). Antioxin SBT final report: Romaqua Group trial. AEB Group.
AEB Group. (n.d.). Improving flavour stability during beer aging: Antioxin SBT.
AEB Group. (n.d.). Antioxin SBT flavour stability: AEB trials. AEB Group.
Bamforth, C. W. (2000). Beer: Tap into the art and science of brewing. Oxford University Press.
Narziss, L., & Back, W. (2009). Abriss der Bierbrauerei (9th ed.). Wiley-VCH.
Kunz, T., & Müller, C. (2015). Oxygen management in brewing. Journal of the American Society of Brewing Chemists, 73(3), 231-239.