Le rôle de l'oxygène dans la fermentation de la bière

When brewing, exposure to too much oxygen during the brewing process can cause oxidation, which can destroy the flavor and aroma of your beer, cider, or wine. Yeast uses oxygen more for energy, so fermentation occurs only when necessary. The process of brewing beer involves several steps, including fermentation, the process of converting sugar into alcohol and carbon dioxide. Fermentation is a critical step in beer production and requires a range of conditions to be successful, including the presence of oxygen. In this article we discuss the role of oxygen in beer fermentation.

What is oxygen?

Oxygen is a chemical element that is a reactive gas and is essential for life on Earth. Oxygen is also an important element in the beer fermentation process.

During fermentation, yeast cells consume sugar and produce alcohol and carbon dioxide. This process requires the presence of oxygen, which is necessary for yeast cells to grow and reproduce. Without enough oxygen, yeast cells will not be able to produce the enzymes and compounds needed for fermentation.
Yet, too much oxygen can also be detrimental to the fermentation process. Excess oxygen can cause the yeast cells to develop off-flavors and aromas, resulting in a less than ideal final product. So, controlling the amount of oxygen during fermentation is very important to ensure high quality beer.

Does yeast need oxygen?

During alcoholic fermentation, yeast produces by-products ethanol (alcohol) and carbon dioxide. Yeast cells are able to use the energy produced by this process to survive and reproduce. In the presence of oxygen, yeast will use oxygen for cellular respiration to produce energy rather than produce alcohol, which is a less efficient process for the yeast. This is why yeast can only produce alcohol under anaerobic conditions, ensuring that the yeast produces alcohol rather than using oxygen for cellular respiration.

How much oxygen is there?

Oxygen demand is variable and depends on the yeast strain used, pitch rate, original gravity of the wort and wort residue level.
The nutritional content of the wort and the amount of oxygen consumed by the wort affect the yeast’s need to function . In an environment where the wort contains enough unsaturated fatty acids but insufficient sterols, oxygen is required for sterol synthesis. Yeast grown in a low-oxygen environment will have higher demands while brewing because sterol synthesis will be limited; yeast grown in oxygen-rich conditions will have less demand because the compounds have already been synthesized and the yeast is in an ideal fermentation state.

Oxygenation method

The best way to dissolve oxygen into the solution is to inject pure oxygen through the sintered stone in line during break-in. There are some brewing devices that can increase the solubility of injected oxygen. Greater solubility is achieved by creating a confinement into which oxygen is injected, then a much less restrictive chamber, and then another confinement. This design creates turbulence, which allows for longer contact time and mixing between the oxygen bubbles and the wort, thereby increasing the rate of oxygen transfer to the wort. The amount of pure oxygen or air required to achieve adequate dissolved oxygen levels depends on many factors, which vary from brewery to brewery.

Factors affecting oxygen levels in beer fermentation

Yeast Type: Different types of yeast have different oxygen needs. For example, ale yeast generally requires more oxygen than lager yeast.
Temperature: The temperature of the fermentation environment also affects the amount of oxygen present. At lower temperatures, oxygen is less soluble in the wort. So, lower temperatures may result in lower oxygen levels.
Oxygenation techniques: The method used for wort aeration (the process of introducing oxygen into the wort) can also affect oxygen levels during fermentation.

How to control oxygen content in beer fermentation?

Correct yeast handling: Correct yeast handling is also important to control oxygen levels during fermentation.
Temperature control: Maintaining a constant temperature during fermentation helps control the oxygen content in the wort.
Proper wort aeration: Proper wort aeration is essential to ensure that the yeast cells have enough oxygen for fermentation.
Use of headspace blanket: A headspace blanket is a layer of gas located on top of the fermentation vessel that helps prevent oxygen from entering the wort.

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