Oxygen in beverages

Oxygen is a key quality control parameter because it can negatively affect the final product in many ways. Therefore, it needs to be closely monitored. Oxygen can lead to reduced shelf life, flavor deterioration, alteration of color, and degradation of certain ingredients.

The physical and chemical impact of oxygen has different root causes, depending on the product and package type. In the case of beer, the presence of yeast leads to oxygen consumption, and thus to a reduction in the oxygen concentration. In soft drinks, on the other hand, the decrease in oxygen content over time is caused by the oxidation process of ingredients such as fruit juices, vitamins and flavors. Soft drink producers often aim for the so called “air in can” amount, which is defined as the air content present within the whole package, including nitrogen and oxygen gas.

For products packed in metal cans, dissolved oxygen is the main cause of corrosion, making it an even more important key parameter in quality control. The corrosion process is accelerated with higher oxygen concentrations, significantly affecting the quality of the final product. Monitoring and controlling the oxygen content in the packaging step is crucial for preventing corrosion. (Davis 1999)

Oxygen concentrations can be measured using different techniques. The most relevant methods are: 

• Chemical analysis (Winkler titration)
• Electrochemical method (Electrode)
• Optochemical method (Optode)

While instruments based on chemical analyses are no longer state-of-the-art, electrochemical and optical methods are precise and accurate measuring techniques used in many different instruments.

However, conditions that contribute to accuracy must be considered, including proper standard operating procedure upon usage, sensor geometry and design, environment, and calibration/adjustment. 

The advantages of the optochemical method are:

• No consumption of oxygen during measurement
• No stirring necessary 
• No use of chemicals

Sensors based on optochemical methods consist of a luminescent dye on a carrier material. The sensor is in direct contact with samples, either in the liquid or gaseous phase. 

An optochemical oxygen sensor works by using a special dye that fluoresces when exposed to light. When there is oxygen around, it interacts with the dye and reduces the fluorescence through a process called dynamic quenching. The higher the level of oxygen, the less the dye will fluoresce. By measuring the intensity of the fluorescence, it is possible to determine how much oxygen is in the environment.

The correlation between O₂ concentration and emission intensity is summarized in Table 1. 

More information can be found here: Optochemical oxygen sensor

The key production steps for oxygen monitoring depend on the industry. Table 2 summarizes the steps where oxygen monitoring is necessary within the production of beer: 

Table 2: Key steps including oxygen monitoring throughout beer production.

Table 3 and Table 4 summarize the steps where oxygen monitoring is necessary within production of soft drinks and wine, respectively. 

Table 3: Key steps including oxygen monitoring throughout soft drink production.

Table 4: Key steps including oxygen monitoring throughout wine production

For example, if there are issues with the syrup mixing, this will result in increased dissolved oxygen readings, whereas problems with package seaming lead to increased headspace oxygen values. 
Moreover, hardware-related issues can also contribute to elevated oxygen levels, such as: 

• De-aeration systems
• Insufficient purging of tanks and pipes upon storage 
• Leaking pumps, valves and pipes
• Issues with filtration aid dosing systems 
• Outdated separator systems 

Instruments based on optical oxygen sensors may display different influencing factors compared to other techniques. Some factors which contribute to accuracy and reproducibility are summarized in Table 5.

Table 5: Influencing factors on oxygen measurements and their origin.

After filling the soft drink into the package, the ratio between headspace oxygen and dissolved oxygen is approximately 0.9:1. After sample preparation, the oxygen molecules will migrate from the liquid into the headspace. However, the overall total package oxygen concentration will remain constant. 

In addition to the typical applications that mainly measure dissolved oxygen concentration in-line, at-line or in the laboratory environment within industries such as soft drink, beer and wine production, there is a constant need for oxygen measurement in various other applications. 

Headspace and total package oxygen concentrations are becoming increasingly significant. Monitoring these parameters, in addition to dissolved oxygen, provides insights and information on which manufacturing process needs to be verified for proper functioning.

The demand for oxygen monitoring in the food industry is increasing, since the presence of oxygen may contribute to microbial growth and cause oxidation of e.g. fats and proteins. 
Examples of possible applications include: 

• Tetra-Pak packages 
• Plant-based drinks 
• Milk 

Further industries where dissolved oxygen measurement is relevant are:

• Power plants
• Pharmaceutical industry
• Medical research industry

In quality control within the beverage industry, the measurement of dissolved oxygen is a fundamental requirement. This critical parameter holds significant importance due to the substantial impact on the final products. Maintaining low levels of oxygen throughout the manufacturing process is the goal, meaning continuous monitoring is necessary. 
Through effective control of this variable, beverage producers can uphold superior quality standards, reduce costs and consistently meet customers’ expectations. Filling and packaging processes, particularly, can be optimized and errors can be detected immediately at the production line by continuous monitoring of dissolved oxygen, headspace O₂ and total package oxygen. 

Manufactures are investing in instruments that enable accurate and precise measurements to meet the requirements and demands. State-of-the-art technologies like luminescence quenching in optochemical sensors are indispensable for achieving the necessary accuracy and precision. 

Such sensors can be used either in-line, at-line or in the laboratory environment, providing a comprehensive overview across the entire production line. 

For more information about carbon dioxide in beverages, see the corresponding Anton Paar Wiki Article: Carbon Dioxide in beverages.

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Davis, J. R. Corrosion of Aluminum and Aluminum Alloys. ASM International, 1999.
Howard, G. A., and J. D. R Mawer. "The determination of dissolved oxygen in beer." J. Inst. Bew. , October 4, 1976: 144-152.
Janßen, Georg, und Karin Dr. Biebernik. "Oxygen the importance of measurement in soft drinks." Soft Drinks International, Oktober/November 2019: 74-77.
Merima Cajlakovic, Alessandro Bizzarri, Christian Konrad, Hannes Voraberger. "Optochemical Sensors Based on Luminescence." (American Scientific Publishers) 7, 2006.
Rana, Muhammad Aadil, Muhammad Madni Ghulam, Roobab Ume, ur Rahman Ubaid, and Zeng Xin-An. Quality Control in the Beverage Industry. Academic Press, 2019.