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 Principally on Beer (Sulphur Dioxide)
Sulphur Dioxide (SO2) is produced in beer by yeast but may also be added to beer as an antioxidant. It can trigger asthma and allergic rhinitis, so measuring the concentration in beer is important to ensure the beer is safe to consumers. There are a number of methods for the determination of total SO2 in beer; some are historic and one fairly hazardous.
Sulphur dioxide by distillation
In the Monier-Williams distillation method, we remove SO2 from beer acidified with orthophosphoric acid by distilling it with steam (or nitrogen or CO2) before oxidising it with hydrogen peroxide into sulphuric acid. The sulphuric acid is then titrated with sodium hydroxide. We calculate the total SO2 from the amount of sodium hydroxide used to neutralise the sulphuric acid.
A video showing the procedure undertaken on wine is here:
Note, this is for illustrative purposes only and is not a recommendation or endorsement of a particular supplier’s product.
In another distillation method, we pass vapour from a steam distillation into an iodine solution. The iodine solution is then titrated with a standard solution of sodium thiosulphate with starch as an indicator. This method is more accurate than the Monier-Williams method at lower levels of SO2.
This method is shown in this video:
Note, this is for illustrative purposes only and is not a recommendation or endorsement of a particular supplier’s product.
Sulphur dioxide by colourimetry
One method for colourimetric determination of SO2 is based on the reaction between SO2, r-rosaniline, and formaldehyde. The sample reacts with r-rosaniline to form r-rosaniline sulphite, a coloured compound, and the absorbance of the solution is measured at 550 nm. r-Rosaniline is a known carcinogen so this procedure is falling out of favour.
In another spectrophotometric determination of SO2, we use nitrogen to strip the SO2 from the acidified beer. The SO2 vapour is then absorbed in a buffered solution of 5,5-dithiobis (2-nitrobenzoic acid) (DTNB). The absorbance of the DTNB solution is measured at 415 nm by a spectrophotometer.
The Thermo Scientific Gallery Beermaster is an automated system which can handle samples of beer without pre-treatment. The Gallery Beermaster uses the reaction of DTNB with SO2 at 37 °C to produce a sample that it analyses in a discrete photometric analyser at 405 nm. The manufacturers report that the results are in line with the r-rosaniline method. The Gallery Beermaster methods are yet to be accepted by EBC, ASBC, or MEBAK.
Here is a video showing the Gallery Beermaster:
Note, this is for illustrative purposes only and is not a recommendation or endorsement of a particular supplier’s product.