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.
Yeast
Yeast produces the majority of flavours found in beer. These have been adequately described in the Fermentation unit (lesson 4), but we will examine further, yeast’s direct influence on flavour, as well as carbon dioxide – one of the principle products of fermentation.
Yeast flavour
Yeast, if not removed after active fermentation, can autolyse (or burst open), following membrane disruption, releasing its contents. This is a particular risk if the beer is not adequately cooled at the right time. Other factors, such as prolonged cropped yeast storage and presence of high concentrations of alcohol and CO2, together with warm temperatures, can also induce autolysis.
The resulting flavour changes may be complex due to the amount of compounds released; however, the principle flavour change is referred to as yeast-bite bitterness or cooked yeast extract (Marmite or Vegemite).
Carbon dioxide
Carbon dioxide is integral to beer flavour. Anyone who has consumed a flat beer will know what we are talking about. Beer without carbon dioxide is lifeless and unpalatable.
Carbon dioxide in the beer acts on the trigeminal nerves mentioned at the start of this lesson. It produces a tingle sensation in the mouth, something that is emphasised by the lower pH and temperature.
This is a stimulation of pain, something like a small electric shock.
It is noticeable that different beer styles call for various levels of CO2, ranging from 1.2-3.5 volumes. Higher levels of CO2 are associated with mouthfeel descriptors such as ‘prickling’, ‘lively’ and ‘refreshing’.
Cask ales have low carbonation, accentuating malt and hop flavours and supporting sessionability. Examples of high carbonation beer include Hefeweizen, Trappist, Belgian Strong Golden Ale and Witbier.
Nitrogen
Nitrogen is not a product of fermentation. It is introduced into the beer either just before or during packaging, as well as during draught beer dispense. It is used in conjunction with low levels of CO2 and reduces the extent of CO2 tingle and acidic flavour. The small stable N2 bubbles replace the tingle and acidic flavour with a sensation described as creamy.