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.
Taints from Contact Materials
The two main sources of these taints are from the water supply and packaging raw materials.
Earthy or soil taints
Bacterial and algal growth in water can lead to taints in beer. Geosmin (damp soil, sugar beet or beetroot) is a taint associated with moderate consumer rejection. Methoxypyrazine imparts an earthy taint to beer. It is described by consumers as ‘dirty’ or ‘contaminated’ and is also likely to lead to moderate consumer rejection.
Anisole taints
2,4,6-Trichloro and tribromo-anisole taints arise from contaminated raw materials, specifically wood or cardboard. Their taste threshold is between 10-500 ng/l and gives the same flavour as that found in contaminated wine corks, similar to being corked or that of a musty cellar.
Tribromo-anisole additionally introduces overtones of rubber.
Catty taints
Mesityl oxide gives a catty or ‘tomcat urine’ unpleasant odour to beer. It is transferred to malt through contact with paint or paint products and is associated with a high level of consumer rejection.
Taints from can linings
Cans are coated with lacquer to protect the metal from corrosion. If this lacquer is compromised during manufacture or degraded over time, metallic taints can arise.
Furthermore, the lacquer itself can be a direct or indirect source of taints. Incompletely cured lacquer can produce plastic or medicinal phenolic taints.
Lacquer has also been known to absorb volatiles from packing layer boards, forming cardboard ‘Labox’ taints.
Styrene is another taint that can come from packaging, as well as CO2.