Hach-Lange LZV936 - DR 6000 Brewery Analysis software - Handbuch (Seite 34)

English 34
Accessories
• Reagent flasks with ground-in stoppers, 16 × 150 mm
• Variable pipette 1.0–5.0 mL (BBP065)
• Pipette tips for pipettes (BBP068)
• Boiling water bath
• Water bath at 20 °C (68 °F)
• Spectrophotometer, 570 nm
• 10 mm rectangular cuvette OS
Reagents
• Color reagent: Dissolve 10.0 g di-sodium-hydrogen phosphate
(Na
2
HPO
4
x 12 H
2
O), 6.0 g potassium di-hydrogen phosphate
(KH
2
PO
4
), 0.5 g ninhydrin, 0.3 g fructose in dist. H
2
O and fill up to
100 mL (This solution can be stored for 2 weeks in a dark flask. The
pH value must be 6.6–6.8).
• Thinner: Dissolve 2 g potassium iodate in 600 mL dist. H
2
O and
add 400 mL 96 % ethanol
• Parent solution: Dissolve 107.2 mg glycine in 100 mL dist. H
2
O.
Store this parent solution at 0 °C (32 °F).
• Standard solution: Fill up 1 mL parent solution with dist. H
2
O to
100 mL. This standard solution contains 2 mg/L amino nitrogen.
Sample preparation
1. Dilute wort 100 times, beer 50 times (1–3 mg/L amino nitrogen).
2. Analyze the sample, standard solution and the blank value three
times each.
3. Pipette 2 mL of the diluted sample or the standard solution or the
dist. H
2
O into a reagent flask.
4. Add 1 mL color reagent and mix.
5. Loosely seal the reagent flasks with glass stoppers to prevent loss
due to evaporation.
6. Heat the reagent flasks for exactly 16 min in a boiling water bath,
then allow to cool for 20 min in the water bath of 20 °C (68 °F).
7. Add 5 mL of thinner.
8. Measure the extinction within 30 min in a 10 mm rectangular
cuvette at 570 nm against the equivalently treated blank value
(dist. H
2
O + color reagent).
9. Correction for dark worts and beers (carry out three times)
a. Add 2 mL of the diluted sample to a reagent flask.
b. Add 1 mL dist. H
2
O instead of the color reagent and proceed
as described above.
c. After adding 5 mL of thinner measure against dist. H
2
O.
Results specifications
In mg/L without decimals
Accuracy
r = 17
R = 28
Standard values
Cast wort (12 %): 200–250 mg/L
Beer (12 %): 100–120 mg/L
For a satisfactory primary and secondary fermentation approximately
220–250 mg/L of free amino nitrogen should be present in the engaged
wort.
Interferences
Because this test measures small amounts of amino acids,
contamination must be avoided. The carefully cleaned flasks must only
be touched on the outside. Ground-in stoppers etc. must be handled
with tweezers.
Literature
MEBAK brew-technical analysis methods, 4th edition 2002
Volume II, P. 62 et seq