The Importance of Oxidation in Beer Wort

Oxygen plays a special role in the entire beer brewing process. Oxygen is necessary to ensure adequate growth of yeast cells during the lag and exponential phases of fermentation. Many people choose the simple stirring aeration method. If you want to introduce oxygen into the cooled wort, mixing oxygen with hot or warm wort will inhibit bacterial growth and increase the possibility of beer contamination. Always make sure that the wort is cooled to the optimal temperature immediately after the boil is completed and before aeration.

Why does yeast need oxygen?

At every stage of the post-fermentation beer brewing process, oxygen is beer's number one enemy. Because it destroys the beer's appearance, aroma, and most importantly - flavor, this process is called oxidation.

During the brewing process, the wort is boiled, which removes many unwanted compounds, makes the wort sanitary and ready for the yeast to work, but also removes most of the oxygen in the wort.

How much oxygen is needed?

Most textbooks recommend a standard dissolved oxygen rate of 8-10 ppm (mg/L) for a moderately strong wort. 5 ppm is considered the minimum standard. 8 ppm of dissolved oxygen can be achieved using normal atmospheric air, but above this level pure oxygen must be used. The key here is to understand that we are talking about dissolved oxygen, and the rate at which oxygen dissolves in wort depends on many factors, including the temperature of the wort, the specific gravity of the wort, and the size of the bubbles.

Many factors determine the amount of oxygen required by yeast. For example, the type of yeast strain, the amount of yeast inoculated, the starting specific gravity of the wort, and the amount of trub in the wort. The ability of the wort to absorb oxygen depends on factors such as specific gravity (sugar content) and temperature. The higher the specific gravity or temperature of the wort, the less oxygen it will absorb.

How to introduce oxygen into wort?

There are many ways to introduce wort, but there are two main methods: aeration and oxygenation. Aeration is the addition of air to the solution, while oxygenation is the addition of pure oxygen to the solution. The difference between the two is that air is only about 20% oxygen. Due to the different composition, using pure oxygen is the faster method. Both methods are performed after the wort has been boiled and cooled to fermentation temperature.

Aeration Methods

Ways to add air circulation when homebrewing:

• Stirring the wort with a masher, stirrer or other implement

• Using a paint stirring attachment on a drill

• Covering and shaking the fermenter or jar

• Pouring the wort between two fermenters or carboys

• Using a mesh filter to create a splash effect when transferring to the fermenter

Since the added air is about 21% oxygen, it may take 15-20 minutes to introduce the required amount of oxygen into the wort. These methods make it difficult to know exactly how much air or oxygen is being added to the wort.

Aeration

Aeration is more effective and efficient than adding pure oxygen to the wort, but requires some additional specialized equipment. Common methods of aeration are:

• Diffuser stones submerged in the wort

• Inline aeration, where oxygen is injected as the wort moves from the kettle to the fermenter

Because pure oxygen is used, the process is faster and more efficient than aeration, and is less risky, as it is unlikely that any microorganisms or other organisms will survive in a pure oxygen environment.

What happens when there is not enough oxygen?

Oxygen in the wort increases germination, which promotes cell growth and improves fermentation efficiency. During fermentation, if more oxygen is not added, the yeast cannot reach the cell mass required for aerobic fermentation, resulting in a long lag time and sometimes even failure to reach the desired final gravity.

The long-term effects of low oxygen levels on yeast polymorphism are also important if the yeast is re-pitched. Lack of oxygen in the early yeast can lead to weakened cells later. This leads to reduced cellular glycogen reserves, cell membranes that cannot withstand the stress of fermentation and a high alcohol content and low pH environment in beer.

Helps Brew Better Beer

Oxygenation of boiled wort after cooling is essential for proper fermentation of brewer's yeast. To be successful, homebrewers must take this important step in the brewing process seriously and select and implement effective wort oxygenation techniques that fit their equipment and budget. Oxygen is essential for the growth of brewer's yeast.