Hach-Lange DR 5000 brewerie analysis, supplementary software LZV570 - Manual (Page 29)

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Working procedures
2.7 Steam-volatile phenols
The degree of fumigation of whisky malts is determined by
analysing steam-volatile phenols. In the beer industry, small
amounts of smoke-dried malts are used to produce “Rauchbiere”
(smoked beers), a speciality of Franconia. Technical problems
during kilning can impart a smoky taste to malts that are intended
for the production of normal beers. This taste is carried through into
the finished product, resulting in complaints from consumers.
Besides organoleptic checks, spectrophotometric determination of
the steam-volatile phenols has proved to be the best method of
identifying malt batches that will impart the undesirable smoky
taste, and of determining the extent to which tank beer and beer
that has gone through the filling stage is affected.
Principle
The phenol fraction obtained with steam reacts in an alkaline
environment with 4-amino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one
(4-aminophenazone) and the oxidising agent potassium
hexacyanoferrate(III) to form a colour substance, which can be
measured with a spectrophotometer after being extracted with
chloroform.
Fields of application
Malt, beer
Measuring range
0–20 mg/kg
Remarks
Wheat beers cannot be analysed by this method, because the
activity of the top-fermenting yeast results in the presence of a
considerable amount of steam-volatile phenols, which do not,
however, impart a smoky taste.
Accessories
• DLFU mill (aperture 1 mm)
• Steam distillation unit
• Separating funnels (1 l)
• Spectrophotometer (460 nm)
• 40 mm rectangular cuvette (OS grade)
Reagents
• Chloroform, ultrapure
• Silicone antifoam emulsion
• Phosphoric acid, conc. (d = 1.71)
• Copper sulphate, CuSO
4
x 5 H
2
O (10%)
• Ammonium chloride (5%)
• 4-Amino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one (2%):
prepare freshly each day