9. Spectrometric determination of the colour of beer

PRINCIPLE

The absorbance of beer is measured at a wavelength of 430 nm. The colour in EBC (European Brewery Convention) units is obtained by multiplying the absorbance by a factor.

EQUIPMENT

• Spektra^TM spectrophotometer,
• micropipette,
• blisters,
• membrane filters, pore size 0.45 µm,
• membrane filter holder.
   

REAGENTS

• deionised water.
   

PROCEDURE

Filter the beer sample through a membrane filter. Dilute the sample, e.g., 10x (only dark beer), so that the transmittance at 430 nm falls within the measuring range.

Pipette 400 µL of deionised-water / blank solution into the hollow of a blister. Use the blue LED at its maximum intensity and set the transmittance for the blank to 100. Then pipette 400 µL of the beer sample into the next hollow of a blister and read the transmittance. Calculate the absorbance and evaluate the colour of the beer sample.
 

CALCULATION

Colour (EBC units) = A x f x 4 x 25 = A x f x 100

A = absorbance of the sample
f = dilution factor

A = - log T 

T = transmittance of the sample

EXPRESSION OF RESULTS

Beer regulations determine that for all types of beer:

• Light beer up to 30 EBC units,
• dark beer higher than 30 EBC units.

Developed and prepared by: Avrelija GOJKOVIČ KUMPERGER, Živilska šola Maribor