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.
The Control of Oxidation Throughout the Brewing Process
So, how does the brewer control oxidation? There are several things they can do, from the choice of raw materials to the manipulation of processing conditions. Let us summarise these using a table.
Table. Process impacts on flavour instability
|
Process |
Aspect |
Control |
|
Malt |
LOX levels |
Use LOX-less malt |
|
Mash conversion |
LOX levels |
Mash in above 60°C to reduce LOX levels |
|
Favour lower mash pH to reduce LOX levels |
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|
Decoction |
Decoction oxygen pickup higher than single mash |
|
|
Superoxide radical formation |
Higher mash pH reduces radical formation |
|
|
Raw materials |
Use higher coloured malts containing antioxidant melanoidins |
|
|
Use lower rice, maize – can be high in lipid |
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|
Vessel material of construction |
Use stainless steel, Copper and iron catalyse ROS formation |
|
|
Wort separation |
Turbidity |
Run brighter worts to give more yeast derived SO2 antioxidant |
|
Weak worts collection |
Avoid collecting as weak worts have increased lipid levels |
|
|
Wort boiling |
Boil time thermal damage |
Longer boils are more thermally damaging |
|
Boil volatile stripping |
Rolling boil is more effective at volatile stripping thus better |
|
|
Liquid adjuncts |
Liquid adjuncts favour stable beer as they contain negligible lipids |
|
|
Hops |
Pellets contain more antioxidant polyphenols than extracts |
|
|
Vessel material of construction |
Use stainless steel, Copper and iron catalyse ROS formation |
|
|
Whirlpool |
Wort clarity |
Clear worts promote SO2 production from yeast |
|
Vessel material of construction |
Use stainless steel, Copper and iron catalyse ROS formation |
|
|
Wort cooling |
Oxygen pickup |
Correct level for yeast promotes health and carbonyl reduction |
|
Fermentation |
Yeast strain |
Some strains are high SO2 producing |
|
Cold break removal |
Remove cold break to create brighter wort therefore more SO2 production by yeast |
|
|
Warm maturation |
Warm conditioning removes VDK’s |
|
|
Vessel material of construction |
Use stainless steel, Copper and iron catalyse ROS formation |
|
|
Maturation |
Oxygen pickup. |
CO2 injection during transfer and sometimes in maturation vessel reduces oxygen |
|
Vessel material of construction |
Use stainless steel, Copper and iron catalyse ROS formation |
|
|
Filtration |
Metal pickup |
Low iron kieselguhr better, KG free filtration (eg membrane), best |
|
Polyphenol removal |
PVPP removes protective polyphenols |
|
|
Dissolved oxygen pickup |
Latest designs packaging lines guarantee lower DO |
|
|
pH |
The higher the pH the lower the ROS produced. |
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|
Packaging |
Dissolved oxygen pickup |
Scavenging crown liners reduce DO |
|
lightstruck reaction |
Cans and kegs protect from lightstruck. Reduced hops offer significant protection. Bottle colour protection is best for brown, then green, and least protective, flint (clear) glass containers |
|
|
Beer analysis |
Dissolved oxygen content |
Lower is better |
|
SO2 |
Higher SO2 is better as staling aldehydes are bound |
|
|
Warehouse |
Lightstruck reaction |
Avoid sunlight and damaging artificial light wavelengths |
|
Temperature |
Lower temperature retards oxidation |
|
|
Stock rotation practices |
Practice FIFO (first in, first out), not FILO (first in , Last out) |
|
|
Temperature |
Lower temperature retards oxidation |
|
|
Distribution and outlets |
Lightstruck reaction |
Avoid sunlight, damaging artificial light wavelengths |
|
Agitation of containers |
Avoid where possible as oxygen is introduced into the liquid |
|
|
Time |
Store as short as possible |
|
|
Stock rotation practices |
Practice FIFO, not FILO |
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|
|
Temperature |
Lower temperature retards oxidation |
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Inventory control |
Shelf life |
Best before date on package |