Lesson 4 - Wort and Beer Analysis
This lesson looks at how to analyse the composition of wort and beer. It covers the current methods for each analysis, outlining the basics of how they are undertaken. It then explains the methods and standards used to ensure that analysis is both precise and accurate. Finally, it discusses how laboratories collaborate so that proficiency levels can be determined.
Analyses on Wort and Beer (Bitterness and Colour)
Bitterness is, to a certain extent, what makes beer, beer. High levels of bitterness are loved by some consumers and hated by others. Consistently right levels are essential for the success of a brand, so we now look at how we measure it.
Bitterness Units (BU) by spectrophotometry
We can measure the IBU of our beer by extracting bitter substances into the solvent 2,2,4 trimethylpentane (iso-octane) and then measuring its absorbance at 275 nm in a spectrophotometer. The absorbance figure is multiplied by 50 to calculate the IBU of the sample. There is an automated version of this analysis available called the Skalar SP2000 Beer Analyser where the activities normally undertaken by hand are completed by robotics.
Here is a video of the spectrophotometric analysis of IBU.
An IBU is roughly equivalent to 1 mg/L of iso-α-acids but they are not the same thing. This method is not suitable for the analysis of beers produced using reduced iso-α-acids hop products.
Bittering compounds by HPLC
We can use HPLC to measure total iso-α-acids as well as to quantify the individual acids and isomers. The solvent used for sample preparation is methanol and the iso-α-acids of interest are used as an external standard. A UV detector is used to detect the compounds as they leave the column at 270 nm. The equipment required to complete the analysis is very expensive and requires operation by skilled personnel. Results are reported in mg/L for the acid in question.
The Gallery Beermaster automatically processes a degassed sample of beer to produce a bitterness measurement.
Colour by spectrophotometer
Beer colour is characteristic of style, and the customer of a brand expects the correct colour. Beer colour can be measured in a spectrophotometer. A degassed and filtered sample of beer is measured at 430 nm in a spectrophotometer. The colour in EBC is calculated by multiplying the absorbance by 25, and in SRM units by 12.7. ASBC have two versions of this method for wort based on sample preparation: in the celite method, the sample is first mixed with kieselguhr; in the filter paper or discs method, paper filters are used.