Beer Bitterness Testing


Beer Bitterness Testing and Other Quality Controls for the Brewery

Although not all wine lovers may be inclined to agree, the product of the fermentation of malted grains, flavoured by the addition of hops, is every bit as complex and varied as that resulting from the fermentation of the fruit of the vine. Connoisseurs of the golden brew can be just as obsessed with the finer details of its composition and the effect that this can have upon its taste, its aroma, its appearance and, of course, its alcoholic content.

The art of the brewer has its origins in prehistory and is thought to date from around 6000 BC. Today, the process begins by steeping a suitable source of starch in water. In most cases, the starchy material chosen will be some form of cereal grain, of which barley now tends to be the most popular. The fermentation is achieved by the addition of yeast and, as one of the products of the reaction is sugar, hops are added to ensure that the beer displays the characteristic degree of bitterness that makes it more palatable to the drinker. In a modern brewery, testing is carried out to measure just how bitter the final product may actually be.

As one might imagine, this is a somewhat subjective quality and, as such, one that depends upon an individual’s palate. So, if in practice, it was to be determined by a human taster, one could certainly not hope for any degree of uniformity. Instead, such measurements are based upon the concentration of certain key compounds that are known to be responsible for this particular quality, found to be present in a given batch. The compounds in question are formed by the isomerisation of substances known as humulones and alpha acids, present in and extracted from the hops, once they have become dissolved in the wort and subjected to heat.

Because the origin of this quality is chemical in nature, it may be evaluated using a technique commonly applied in chemical analyses. In the case of beer, its degree of bitterness may be determined precisely by spectroscopic testing of a suitable extract of the wort. The pH of the latter must first be reduced, causing the isomers to become hydrophobic. Thereafter, these compounds can then be extracted using a suitable organic solvent. Reading its absorbance at a wavelength of 275 nanometres allows the concentration of responsible isomers present to be calculated by comparison with an extract of known concentration. The results are then expressed using the so-called IBU (International Bittering Units) scale. High Performance Liquid Chromatography (HPLC), Mass Spectrometry and Fluorescence spectroscopy have all been used for this purpose, but while the first of these is much slower, the others are far more expensive.

Another quality that is important to the consumer is colour, which can be determined using a simple comparator. The colour depends both upon the ingredients and the particular physical and chemical processes employed by the brewer. The colours range from a pale yellow for lager and Pilsner, to near black for stout. The alcohol content is determined from the difference in specific gravity of the wort, prior to, and following fermentation.

Better still, chat to IEPSA about the innovative BeerLab analyser for rapid determination of colour, pH, alcohol content and bitterness testing in multiple beer samples.

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