Question

In 1516 the Duke Wilhelm IV of Bavaria introduced the german purity law for brewing beer. More than 500 years later the law is still strictly enforced and it states that for brewing beer you must not use any ingredients other than water, barley and hops. Barley is contributing starch that is broken down to di- and monosaccharides during the fermentation process. Production of some cheap (and in Germany illegal) beer, however, utilises sucrose as sugar. Using the indicated reagents, describe an experiment with suitable controls that allows authorities to determine if a beer was produced using barley or sucrose. Explain the carbohydrate chemistry behind the test to justify your answer.

In addition to general laboratory equipment the ONLY reagents available to you are:

• a beer sample
• the enzymes invertase and maltase
• the Somogyi-Nelson reagents for the determination of reducing sugars.

i) concisely describe the tests that you would use

ii) concisely describe the observations in case that the beer was made with barley,

iii) concisely describe the observations in case that the beer was made with sucrose,

Answer 1

Answer i)

Test using Somogyi-Nelson reagents -

• Take 2mL of beer sample.
• Add 1mL of alkaline copper tartarate reagent (Somogyi reagent) to the sample.
• Place the sample in boiling water bath for 10 minutes.
• Cool the tubes.
• Add 1mL of arsenomolybdic acid (Nelson's reagent) to the sample.
• Check for the blue color development.

Answer ii)

Somogyi-Nelson reagent is used to check the presence of reducing sugars in the sample.

• If the beer is made of barley, maltose will be present, as it is the fermented product of barley. Thus the sample at the end of the test will give a blue colored reaction.

Answer ii)

• If the beer is made of sucrose, reducing sugars will be absent. Thus the sample at the end of the test will not give a blue colored reaction.