Hach-Lange DR 5000 brewerie analysis, supplementary software LZV570 - Manual (Page 12)

12
Working procedures
2.2 Total polyphenols (EBC method)
Principle
Polyphenols react with iron(III) ions in an alkaline solution to form
coloured iron complexes; the resulting brown colour is measured
with a spectrophotometer.
Fields of application
Beer, worts
Measuring range
0–800 mg/l
Accessories
• Centrifuge
• Spectrophotometer (600 nm)
• 10 mm rectangular cuvette (OS grade)
Reagents
• Carboxymethylcellulose-ethylenediaminetetracetic acid
solution (CMC-EDTA-Na):
a. Weigh out 10 g CMC (low viscosity) and 2 g EDTA-Na
2
.
b. Dissolve these substances in about 500 ml H
2
O while
stirring. When they are completely dissolved, fill up to 1 l
with H
2
O. If necessary, clarify by centrifuging.
• Ammonium iron(III) citrate (3.5%):
a. Dissolve 3.5 g ammonium iron(III) citrate, green (16% Fe),
in H
2
O and make up to 100 ml. The solution must be
completely clear. It remains stable for about 1 week.
b. Ammonia, dilute:
Dilute 1 part concentrated ammonia (d = 0.91) with 2 parts
H
2
O.
Sample preparation
1. Shake beer to expel carbon dioxide.
2. Clarify cloudy wort or beers by centrifuging.
3. Mix 10 ml test solution and 8 ml CMC-EDTA solution
thoroughly in a 25 ml measuring flask.
4. Add 0.5 ml iron(III) solution and mix thoroughly.
5. Add 0.5 ml dilute ammonia solution and mix thoroughly.
6. Make up to 25 ml with H
2
O and mix.
7. Wait 10 min, then measure the absorbance in a 10 mm
rectangular cuvette at 600 nm against a blank sample.