Hach-Lange LZV936 - DR 6000 Brewery Analysis software Benutzerhandbuch
Seite 37
English 37
•
Phenol standard solution: Dissolve
1.000 g phenol in dist. H
2
O to 1000 mL (1 mL=1 mg). The solution
must be clear and colorless. From this solution freshly prepare
thinners for constructing the calibration curve 0.02–0.1 mg/L as
required.
•
Dilute ammonia, diluted (1+4):
1 part concentrated ammonia (d=0.91) with 4 parts dist. H
2
O.
Sample preparation
1.
Steam distillation
a.
Add 50 g coarse malt with 500 mL dist. H
2
O (for tests of
300 mL of beer) to a distillation flask.
b.
Add 3 mL copper sulfate solution.
c.
Adjust the pH value through addition of phosphoric acid to
pH<4.
d.
Add the silicone anti-foam emulsion.
e.
Perform steam distillation until 300 mL have been recovered.
2.
Color reaction
a.
Add 10 mL of Ammonium Chloride solution to the distillate. For
real smoke malts or whiskey malts, use correspondingly less
distillate (for example 100 mL).
To produce the blank value, introduce 300 mL dist. H
2
O
instead of distillate and also add 10 mL ammonium chloride
solution.
b.
Shake the solution.
c.
In each case (distillate and blank value) adjust the pH value
with ammonia to pH 10.2 ± 0.1.
d.
Transfer each solution to a 1 L separatory funnel.
e.
Add to each 3 mL 4-amino-2,3-dimethyl-1-phenyl-3-pyrazolin-
5-one and 3 mL potassium hexacyanoferrate(III).
f.
Shake the solution.
g.
Allow the solutions to rest for 3 min.
h.
Shake each separatory funnel 3 times at one minute each
with 10 mL chloroform to extract.
i.
Wait 10 min each for the phase separation.
j.
Filter the chloroform extracts through paper filters into 25 mL
volumetric flasks.
k.
Rinse the filters with some chloroform.
l.
Fill with chloroform respectively up to the mark.
m.
Measure the chloroform extract (prepared distillate) in 40 mm
rectangular cuvette at 460 nm against the prepared blank
value.
3.
Calibration values
a.
With phenol standard solutions of 0.02–0.1 mg/L (introduce
300 mL) carry out steam distillation and convert as described
above.
Results specifications
In mg/kg with two decimals (or mg/L for beer)
Accuracy
Vk = ± 5 % (repeat error)
Target values
Malts: < 0.2 mg/kg: no smoke taste expected
Beers: < 0.03 mg/L: harmless in most cases
The penetration of the smoke taste depends on the beer composition,
which is why the named lower limit applies only with reservations.
Literature
MEBAK brew-technical analysis methods, 3rd edition, Volume I
Procedure for steam-volatile phenols
1.
Prepare the blank value and the samples according to the work
procedure.
2.
Select STORED PROGRAMS > SELECT BY NUMBER.
3.
Enter the number 2009 for the program "Steam-volatile phenols".
Confirm with OK.
4.
Press START to start the program.
5.
Enter the blank value (see sample preparation) and press ZERO.