Hach-Lange DR 5000 brewerie analysis, supplementary software LZV570 - Manual (Page 39)

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Working procedures
2.10 Iso- α-acids and α-acids
Principle
The bitter substances are extracted from the acidified sample with
iso-octane. Certain substances that cause interference are
removed by washing the extract with acidified methanol, and the
concentrations of iso-
α-acids and α-acids are determined by
measuring the absorbance in alkaline methanol at 255 nm and
360 nm.
Fields of application
Beer, wort
Measuring range
0–60 mg/l
Accessories
• Centrifuge tubes with solvent-tight screw tops (100–110 ml
content)
• Shaker
• Centrifuge (3000 rpm)
• Spectrophotometer (255 nm and 360 nm)
• 10 mm rectangular cuvettes (QS grade)
Reagents
• Hydrochloric acid, 6N
• Iso-octane (2,2,4-trimethylpentane), of spectroscopic purity
• Sodium sulphate, anhydrous
• Methanol
• Hydrochloric acid (4N)
• Sodium hydroxide (6N, carbonate-free)
• Acidic methanol solution: Mix 64 ml methanol and 36 ml 4N
hydrochloric acid (prepare freshly each day).
• Alkaline methanol solution: Take 0.2 ml 6N sodium hydroxide
and make up to 100 ml with methanol (prepare freshly each
day).
Sample preparation
1. Clarify wort or cloudy beer by centrifuging at 3000 rpm for
15 min (do not filter).
2. Expel carbon dioxide from beer without losing any foam.
3. Bring the sample to 20 °C, then pipette 50 ml into a centrifuge
tube.
4. Add 3 ml 6N hydrochloric acid and 25 ml iso-octane.
5. Close the centrifuge tube and shake mechanically for 30 min at
optimal mixing intensity.