Quality control in brewery industry - Unlocking Yeast metabolism secrets: Nitrogen and Sulfur Dioxide effects on beer

Nitrogen in the wort and in the finished product is evaluated by detecting free amino nitrogen (FAN) also defined as primary amino nitrogen (PAN). FAN analyses test the concentration of amino acids used by yeast for cell growth and proliferation. Together with ammonia, FAN/PAN constitutes what is known as Yeast Assimilable Nitrogen or YAN. FAN levels in wort are often considered the best indicator of potential yeast growth and are therefore directly related to fermentation efficiency. Yeast needs FAN to grow and reproduce, so theoretically the more you have, the faster your yeast will grow and the more efficient fermentation will be. Yeast consumes most of the FAN in the first 36 to 40 hours of fermentation. This allows them to produce a range of metabolic byproducts, some of which affect the flavor and stability of the finished beer.

There are several reasons why a brewer should measure the FAN content of wort.

If the FAN content in the wort is insufficient, the yeast cannot grow and develop effectively conveying in slow fermentation and production of potentially unpleasant aromas. Inadequate amount of FAN at the beginning of fermentation may contribute to higher SO₂ and diacetyl production. On the other hand, if the FAN content is too high in the wort, the yeast will not be able to assimilate all of it. This will result in residual amino acids in the finished product, which can lead to further post-fermentation chemical reactions and cause premature aging of the beer and sensory defects.

The ideal value of FAN should be between 200 and 250 mg/L, depending on the gravity of the initial wort (or the initial value of fermentable sugars). For wort from high-density beers, it has been observed that an optimal FAN value is between 250-300 mg/L. Whether the quantity is sufficient can be measured in 4 minutes with the CDR BeerLab®. FAN values at the end of the fermentation should be around 30-40% lower on average than the initial value while in the finished beer it has to be as low as possible in order to preserve, over the time, the stability of the product.

Sulfur dioxide (SO₂) in beer mainly originates from yeast metabolism. Yeast converts sulfate to sulfite for amino acid production. The process is controlled by a negative feedback process: if more sulfite is produced than is needed, the excess is released into the beer. The amount of SO₂ released is influenced by the yeast's condition, especially early in fermentation. Poor oxygenation slows yeast development, leading to less SO₂ used for amino acids and more released into the wort. Insufficient FAN in the wort also increases SO₂ production due to reduced negative feedback.

Factors affecting SO₂ production include high wort pH, temperatures between 14-17°C, high sulfate concentrations in water, and high initial gravity. Sulfites are also added to beverages to prevent spoilage and oxidation, with sulfur dioxide being crucial for beer preservation. Breweries often use potassium metabisulfite (K₂S₂O₅), labeled as E224. Some people may have sensitivity to SO₂, causing symptoms like nausea and headaches. Therefore, regulations limit SO₂ concentrations in beer, such as the EU's maximum of 20 mg/L. Levels above 10 mg/L require a "Contains Sulfites" label.

Real-time determination of SO₂ and FAN is essential for uninterrupted production and maintaining fermentation quality. Once again, the determination of these two parameters in real-time is crucial to keep the production running without damaging the fermentation. The CDR BeerLab® offers rapid SO₂ detection in 2 minutes, avoiding wasteful distillation and hazardous methods used by traditional techniques.

As previously mentioned, pH is a key factor in the development of SO₂ and plays a crucial role in controlling enzyme activities during mashing. For example, α-amylase has optimal activity at a pH of 5.6-5.8, β-amylase at 5.4-5.6. Despite its importance, pH management is often overlooked in the craft brewing industry. Throughout the brewing process, pH levels decrease steadily: starting from the water pH of 6.2-7.0 (depending on the type of water used), dropping to 5.5 in the pre-boiling wort, further decreasing to 5.2 during boiling, and finally reaching a pH of 3.9-4.5 in the finished product.

Understanding and managing the levels of FAN, SO₂, and pH throughout the brewing process is crucial for achieving a stable and high-quality beer. Proper nitrogen availability ensures efficient yeast growth, while monitoring SO₂ production helps prevent unwanted sensory defects and regulatory issues. Additionally, maintaining optimal pH levels improves enzyme activity and overall fermentation efficiency. By utilizing real-time analysis tools such as the CDR BeerLab®, brewers can take precise control over these key parameters, enhancing both production consistency and final product quality.