beerIf I mentioned that I recently sampled an amazing new craft beer, you might assume that there is a brilliant artisan behind the brew. Maybe there is. Creating the perfect brew may be part art, but also is a great deal of good beer chemistry. Beer is brewed using the following basic ingredients: water, a source of starch (such as barley, wheat, rice, or corn), and hops. Variations in flavor result from the ingredients and additives used as well as the brewing process utilized.

In fermentation, the yeast Saccharomyces converts sugar to ethanol and carbon dioxide. Besides sugar, nitrogen is the most important nutrient for yeast health and growth. Too little nitrogen results in incomplete fermentation whereas too much nitrogen is responsible for off flavors or spoilage. Nitrogen levels are often assessed through Free Amino Nitrogen (FAN) or Primary Amino Nitrogen (PAN) measurement. Along with ammonia, FAN/PAN constitutes Yeast Assimilable Nitrogen (YAN).

Levels of YAN in wort influence the formation of higher alcohols, specifically ethanol, which contributes to the flavor of beer and further influences the flavor contribution other alcohols will make. Considered a better predictor of healthy yeast growth, viability, fermentation efficiency and resulting beer quality and stability, YAN levels demonstrate enzyme action during malting. Most of the YAN is consumed within the first 36 hours of fermentation. While a YAN level of 150 mg/L indicates complete fermentation, for some higher Alcohol by Volume (ABV) beers, the level can be 250 mg/L or higher. Craft breweries, because they often use all malt wort, need to monitor YAN levels in order to control haze and the production of off flavors from higher alcohols. Excess YAN levels can also provide the best environment for growing organisms that will spoil beer.

Traditionally, the ninhydrin method has been used to estimate amino acids, ammonia, and the terminal nitrogen groups of peptides and proteins (YAN) and is listed as the method of choice by the European Brewery Convention (EBC), MEBAK, and American Society of Brewing Chemists (ASBC). Recently, the EBC approved a simpler and more rapid method called alpha amino nitrogen by OPA (NOPA) which determines the amino acid content in beer using a photometric measurement of OPA (o-Phthaldialdehyde) and NAC (N-acetyl cysteine). A rapid 2-reagent method was developed for a multi-purpose automated discrete analyzer (Thermo Scientific Gallery Plus Beermaster). This method has previously been tested in a side-by-side comparison against the EBC FAN protocol and demonstrated similar results. Furthermore, no additional ammonia measurements were needed. Total analysis time for six samples (60 tests) is approximately 45 minutes. The advantage of using the automated analyzer is its ability to simultaneously measure other analytes like beta-glucan, pH and SO2 on the same sample used for the NOPA measurement.

Additional Resources:

Application Note 71798, Correlation of the Free Amino Nitrogen by O-Phthaldialdehyde Methods in the Assay of Beer

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