Hach-Lange LZV936 - DR 6000 Brewery Analysis software - Handbuch (Seite 33)

English 33
Accessories
• Spectrophotometer, 430 nm (± 0.5 nm)
• 10 mm rectangular cuvette OS
Sample preparation
1. Dilute the sample so that the extinction lies within the linearity of
the spectrophotometer.
2. Filter the sample through a membrane filter. The filtration can be
omitted if the turbidity of the diluted sample is below 1 EBC turbidity
unit.
3. Clarify the beer as required by addition of 0.1 % diatomaceous
earth and a filter upstream of the membrane filter.
4. Measure the extinction (E) at 430 nm against dist. H
2
O (blank
value).
Results specifications
In EBC units with 2 indicative numerals
Interferences
A spectrometric absorption curve does not reflect the color impression of
the human eye, as light of equal intensity in various parts of the
spectrum influences the eye differently. Also the extinction curves are at
430 nm very steep, so that slight measuring errors can occur. There are
also differences during comparison of light beers with diluted dark beers.
Literature
MEBAK brew-technical analysis methods, 4th edition 2002, Volume II, P.
88 et seq
Procedure for beer color
1. Prepare the zero solution and the samples accordance to the work
procedure.
2. Select STORED PROGRAMS > SELECT BY NUMBER.
3. Enter the number 2006 for the program "Beer color". Confirm with
OK.
4. Press START to start the program.
5. Enter the zero solution (dist. H
2
O) and press ZERO.
6. Insert the analysis cuvette with the prepared sample and press
READ.
The result is shown on the display.
Note: In order to analyze further samples, repeat the procedure
from step 6.
Free amino nitrogen (ninhydrin method according to
EBC)
Principle
The examination solution is heated at pH 6.7 with ninhydrin and the
resultant color measured at 570 nm. The method records the amino
acids, ammonia and also the terminal alpha amino groups of peptides
and proteins. Prolin is partially co-determined at the applied wavelength.
The method is not specific to alpha-amino-nitrogen, because gamma-
amino-butanoic acid, which occurs in worts, also develops a color with
ninhydrin.
Application areas
Beer, worts
Measurement range
0–400 mg/L