Lesson 7 - Beer Flavour and Stability SAQ
This lesson allows you to test yourself on the material covered in the lesson on Beer Flavour and Stability and determine the level to which you have met the learning outcomes.
Suggested Response - Q2
**Describe the taints in beer originating from cleaning materials and the steps brewers can take to minimise them.
Response:
Detergent cleaning agents are not normally reactive in beer and taint the product with their base material. Sanitisers are often reactive and produce compounds from reactions with water or beer, which also causes taints.
Caustic soda is the most commonly used detergent in cleaning brewing vessels and mains. It can cause alkaline or soapy taints in beer.
To avoid the risk of tainting, rinses from mains and vessels are analysed for the presence of caustic soda using the dye known as phenolphthalein, which turns a pink colour above pH 8.2. A quantitative test, using a sodium-sensitive electrode, measures the sodium concentration compared with the water. This method can easily be adopted at operator level.
Brewery acid cleaning utilises nitric or nitric-phosphoric acid blends. Tainting beer with acid produces an acidic tasting product with a low pH. Detection can be done by the pH measurement of rinses. For increased sensitivity, disposable nitrate strips are used. Their colour becomes proportional to the nitrate’s concentration.
Chlorinated sanitisers can cause medicinal taints from chlorine reaction with organic molecules forming chloromethanes and chlorophenols.
Chlorine is detected in rinse water using DPD (n n-diethyl-paraphenylenediamine), which is a red colorimetric reaction. Measurement can be taken by using a comparator instrument or simply on colour strips.
Combined forms of chlorine are measured by adding potassium iodide. For a more accurate measurement, a colorimeter is used, which measures the amount of coloured light absorbed by the sample in proportion to the chlorine concentration.
Hydrogen peroxide can oxidise components of beer and form the reactive hydroxyl radical, which catalyse oxidation reactions. It can be measured using colorimetric strips or the titration of liberated iodine from an acidic solution (in the presence of peroxide). Acetic acid is normally combined with peroxide to form peracetic acid.