Hach-Lange LZV936 - DR 6000 Brewery Analysis software - Handbuch (Seite 41)

English 41
Accessories
• Centrifuge flasks with solvent-proof screw closure, 100–110 mL
capacity
• Shaking machine
• Centrifuge, 3000 rpm
• Spectrophotometer, 255 nm and 360 nm
• 10 mm rectangular cuvette QS
Reagents
• Hydrochloric acid, 6N
• Iso-octane (2,2,4-trimethylpentane), spectroscopic purity
• Sodium sulfate, anhydrous
• Methanol
• Hydrochloric acid, 4N
• Sodium hydroxide, 6N, decarbonated
• Acidic methanol solution: mix
64 mL methanol and 36 mL 4N hydrochloric acid (prepare fresh
daily)
• Alkali methanol solution: top up
0.2 mL 6N sodium hydroxide with methanol to 100 mL (prepare
fresh daily)
Sample preparation
1. Clear wort or cloudy beer through centrifuging at 3000 rpm for
15 min (do not filter).
2. Remove the carbon dioxide from the beer without foam loss.
3. Pipette 50 mL of the sample maintained at 20 °C (68 °F) into a
centrifuge flask.
4. Add 3 mL 6N hydrochloric acid and 25 mL iso-octane.
5. Seal the centrifuge flask and shake it mechanically for 30 min at
optimal mixing intensity.
6. Centrifuge to separate the phases and break up the emulsion for
5 min at 3000 rpm.
7. Remove the lower aqueous phase through suction with a pipette
and discard it. Displace the iso-octane phase with enough sodium
sulfate so that the solution is clear after brief vigorous shaking.
8. Pipette 10 mL of the iso-octane phase into a 25 mL volumetric
flask.
9. Add 10 mL acidic methanol solution, seal the flask and mix the
contents by inverting the flask 100 times.
10. Pipette 5 mL of the excess clear iso-octane phase into a 25 mL
volumetric flask.
11. Fill to the mark with alkali methanol solution and mix.
12. Measure the extinction of the iso-octane solution against a blank
value at 255 nm and 360 nm.
13. Blank value preparation
a. Pipette 5 mL iso-octane into a 25 mL volumetric flask.
b. Fill to the mark with alkali methanol solution and mix.
Results specifications
In mg/L without decimals
Accuracy
Vkr = ± 5 %
Standard values
Beer: 10–40 mg/L iso-
 acids, depending on nature, sort, type and origin
(< 2mg/L  acids)
Wort: 15–50 mg/L iso-  acids, depending on beer and bitters yield
1–15 mg/L
 acids depending on degree of isomerization
Literature
Brew-technical analysis methods, 4th edition 2002,
Volume II, P. 116 et seq