By Katie Fromuth, Colorado State University Malt Quality Testing Lab
Understanding the experiences and needs of the customer is an important tool for maltsters in building strong and healthy relationships with the brewers and distillers they support. The ability of a maltster to acknowledge the reasons behind a brewer’s wants and needs can promote a powerful and reciprocal relationship. When a brewer looks at a malt Certificate of Analysis (CoA), hopefully, they are taking all those values and considering what they mean for their process and products. One important value sometimes overlooked on a CoA is free amino nitrogen (FAN). FAN is a broad measurement having important implications in malt and beer however, it is not well understood.
For us to get a better understanding of FAN, let’s start by going back to the fundamentals. Amino acids (proline, valine, tryptophan) are the building blocks of proteins. They are organic chemical structures that have an amino group (-NH2), a carboxyl group (-COOH), and a functional side chain (-R) which is responsible for differentiating the 20 amino acids depending on the structure of that side chain.
In barley, proteins are stored in the endosperm for growing a plant from the seed, similar to how starches are stored. For the plant to use the stored protein, it first forms various enzymes (proteases) during germination to break down proteins into smaller peptides (short chains of amino acids) and singular amino acids. The combined singular or “free” amino acid subunits present in the malt are what we consider FAN. Soluble protein, by contrast, consists of larger peptide chains. On the CoA, soluble protein is also reported as a percentage of the total protein through the soluble/total (S/T) value. FAN and S/T together aim to represent the level of protein modification and are linearly correlated.
But why does a brewer care about the FAN in their malt?
A brewer might have various reasons for considering FAN in the malt they use. Just as the barley kernel needs nitrogenous building blocks to grow into a plant, a brewer’s yeast, Saccharomyces sp., requires FAN. Yeast assimilates available nitrogen in the form of FAN and ammonium present in the wort to synthesize new cell growth and attain optimal fermentation. If there is insufficient FAN in the wort, the yeast cannot grow enough new cells and this results in slow fermentation and development of off-flavors, in turn, affecting time, tank space, effort, and costs to the brewery. If FAN is too high in the wort, the yeast will not be able to assimilate all the FAN. This will result in residual amino acid in the finished product, which can lead to further chemical reactions post-fermentation, and result in beer staling off-flavors1-3. This is a classic “Goldilocks” scenario in which the yeast (and by default the brewer) require the FAN not too low, not too high, but just right. According to Yin, the ideal FAN ranges between 150 – 220 parts per million (ppm), depending on the starting wort gravity3.
It is well understood that excess FAN correlates to beer staling and is negatively correlated to beer stability1-3. Beer stability refers to the capacity of beer to maintain its original quality, flavor, and chemical profile as long as possible. A brewer might not know when their product is going to reach the consumer, so it is essential for beer to be stable for as long a period as possible so when the consumer does get to enjoy the tasty suds, they are fresh tasty suds and the truest representation of that brand.
There are many mechanisms that result in the staling of beer, including oxidation mechanisms (e.g. lipids, free radicals, higher alcohols, and iso-alpha-acids) and aldol condensation resulting in the formation of a cardboard-like or papery off-flavor. However, the majority of beer staling results from amino acids transforming into chemical compounds called “Strecker aldehydes” (SA)3. To simplify the mechanism, a complex cascade of chemical reactions occurs between amino acids and dicarbonyls that form SA when the beer is in its final package. The amino acids are a product of excess FAN at the end of fermentation, and the dicarbonyls are a product of Maillard reactions. Maillard reactions are the interactions between proteins and sugars in the presence of heat and are responsible for the roasted and toasty flavor attributes of malt and beer.
SA reactions accelerate at higher temperatures but will also progress at room temperature at a slower rate. Beer typically has a shelf life of 4-6 months, but SA can form in as quick as one month depending on environmental conditions (light, heat, packaging type)3. The resulting flavor attributes can be generalized as caramel, toffee, nutty, fruity, meaty, and brothy notes. Additionally, research has correlated specific amino acids to their resulting SA and their accompanying sensory attributes3,4. For example, the amino acid valine and its corresponding SA will impart a fruity green apple aroma, the proline SA results in bready characters, and phenylalanine results in pungent floral rose aromas. Many of these aromas could be appropriate for some beers however, if they are misplaced and not part of the beer brand or style profile they will be considered off-flavors. Therefore, it is important to prevent the formation of SA in beer and preserve the original flavor profile.
The potential flavor changes caused by SA formation during beer storage depend on the amino acid profile of the excess FAN at the end of fermentation. This profile will vary depending on multiple factors. Yeast assimilates amino acids in a specific order depending on the importance to the yeast2,3. Proline is the only amino acid that yeast will not assimilate out of the 20 amino acids. Additionally, the amino acid profiles in malt vary depending on the geographical region of where it is grown and barley variety3. Analytical testing to understand the amino acid profiles of malts, brewer’s wort, and finished beer is one opportunity for gaining a better understanding of beer stability however, this analysis remains uncommon.
Beer stability is a complex chemical process in which many factors, not just the malt, will have an impact. FAN and the amino acids that contribute to the value you find on a malt CoA are just a small part of that impact and part of the bigger story maltsters can consider using as a relationship-building tool with their customers. It is the role of both the maltster and the brewer to ensure beer stability is high and consumers are happy.
Sources
- Mallet, J. Malt: A practical guide from field to brewhouse. (Brewers Publications, 2014).
- Briggs, D. E., Brookes, P. A., Stevens, R. & Boulton, C. A. Brewing: Science and Practice. (Elsevier Science & Technology, 2004).
- Yin, X. S. Malt. (American Society of Brewing Chemists, 2021).
- Meilgard, M. C. Vol. 12 151-168 (MBAA Technical Quarterly, 1975).
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