Lesson 6 - Beer Flavour and Stability
In this lesson we will discuss beer flavour and beer flavour stability. This will include the effects raw material has on beer flavour, followed by a discussion on common taints, their flavours and consumer reaction. We will examine the flavour changes that occur during beer storage: focussing on oxidation reactions, the species of oxygen involved, and how we can utilise antioxidants to protect against aged beer flavour change. Finally, we will summarise the selection of raw materials and process optimisations available to improve beer flavour stability.
Strecker Degradation of Amino Acids
Amino acids can react with the di-carbonyl intermediates in Maillard reactions to form corresponding flavour-active aldehydes with one less carbon atom. The flavour contribution of Strecker products is shown below:
Table: Strecker degradation products in beer and their aromas
|
Amino acid |
Strecker degradation product |
Aroma |
|
Valine |
2-methylpropanal |
Grainy, varnish, fruity |
|
Isoleucine |
2-methylbutanal |
Almond, apple-like, malty |
|
Leucine |
3-methylbutanal |
Malty, chocolate, cherry, almond |
|
Methionine |
Methional |
Cooked potatoes, worty |
|
Phenylalanine |
Phenylacetaldehyde |
Hyacinth, flowery, roses |
|
Phenylalanine + phenylacetaldehyde |
Benzaldehyde |
Almond, cherry stone |
Strecker degradation of the amino acid methionine gives methional, which is responsible for the worty flavour of alcohol-free beers. It is also the precursor of dimethyl trisulphide which develops as beer ages.