Bottling is the last beer brewing process during which dissolved oxygen can be added and have a significant negative impact on the aging potential and quality of beer being released to the consumer. Thus, extreme care must be employed in minimizing the amount of oxygen entry at bottling. Oxygen has the potential to dissolve into the beer at every stage of the bottling process. Temperature has an important effect on the oxygen level in beer. It is well known that decreasing beer temperature accelerates oxygen uptake.
Total Package Oxygen
Total package oxygen (TPO) management at bottling is crucial to avoid beer oxidation and is expressed as milligrams per liter (mg/L) or parts per million (ppm). Total package oxygen (TPO) is the sum of dissolved oxygen (DO) in the beer and headspace oxygen (HSO) contents.
After filling, oxygen in the headspace of the bottle is another source of oxygen absorption. This is due, in part, to the variability of the bottle headspace, which is influenced by such factors as beer temperature, solubility of gases in the beer, bottle size, closure, and filling operations. Headspace oxygen usually represents more than 50 percent of the TPO, which makes it the biggest reservoir of oxygen in a bottle.
After bottling, oxygen measurement should be initiated as soon as the bottles come off the bottling line. If there is any delay in measuring the oxygen, the reading will be artificially low because the oxygen has had a chance to bind with other compounds and will not be detectable. If the beer was exposed to oxygen in the cellar before packaging, it is likely that the oxygen is already bound and undetectable. Always measure packages immediately after filling and before pasteurization, because the heating process allows dissolved oxygen to react rapidly with the beer.
Gas Extraction and Piercing Systems. Gas extraction and piercing systems are used for measuring TPO, i.e., dissolved oxygen. For TPO measurement, typically the bottle is shaken for approximately 5 minutes to equilibrate the gas phase (in the headspace) and dissolved gases in the beer before the oxygen in the beer is measured.
Oxygen Sensors. Optical sensors allow for non-invasive measurement of dissolved oxygen and headspace oxygen through the glass bottle wall.
Sources of Dissolved Oxygen
Any time beer is moved, brewers run the risk of the product picking up air. Air pickup in beer before it reaches the filler most often comes from transfer and filtering operations. The usual suspects are the bright beer tanks, the seals and gaskets along the pathway, and the pumps. To help displace air that may have been picked up during transfer and filtering operations, brewers can perform final carbonation in the bright tank before sending it to the filler.
Oxygen in the Package vs. Shelf Life
The biggest issue that a brewer faces is the shelf life of the product. This is a measure of how long the beer can survive before the flavor or the cloudiness of the beer changes to a point where it doesn’t represent the beer brand’s desired quality. The flavor of the beer does change over time. Natural aging occurs when the compounds in the beer react with each other and form new compounds. These new compounds can impart a flavor to the beer, and over time, this becomes notable to the consumer. Apart from natural aging temperature can affect the aging process, not to mention the presence of yeast.
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