Maturation and stabilsation

What are the qualities of green beer post fermentation?

• flavour not fully matured

• Flavour and colour may require adjustment

• Lacks sufficient carbonation

• Turbid

• Physically and microbiologically unstable

What is meant by the term finishing processes?

Maturation (lagering or aging), carbonation, clarifying and stabilisation address this and are know as finishing processes

What is secondary fermentation?

Fermentation of residual or additional sugar by yeast after peak primary fermentation subsides.

Controlled by low temperature and low yeast count

Examples include cask or bottle consigned beers, kräusen fermentations and lagering

What occurs briefly in the storage/aging process?

Yeast concentration and or temperature too low to permit fermentation.

Modification of primary fermentation characters for maturation (e.g., diacetyl rest), CO2 injection for carbonation

In traditional cask conditioned or bottle conditioned ale, with the addition of priming sugar what may also be added?

Fining agents, hops, or hop products as well as colour/flavour adjustment - caramel, roasted malt extract

Casks/bottles then sealed and held in order to “come to condition”

Results in carbonation and yeast sediment

What is Kräusening?

The addition of sugar post primary fermentation is made by addition of the kräusen: addition of 10% by volume of freshly fermenting wort (which is at peak fermentation rate)

Held for 1-3 week at about 8C

During this prolonged cold deco day fermentation beer flavour matures, beer is carbonated and clarified by sedimentation

What occurs in traditional lagering?

Same general practice as kräusen fermentation except sugar for the prolonged secondary fermentation is unfermented original sort.

I.e., beer is cooled to about 8 C or below and moved to secondary vessel before primary fermentation is complete

May last up to several weeks or months

As with kräusening, during this prolonged cold secondary fermentation beer flavour matures, beer is carbonated and clarified by sedimentation

What is the lengthened primary fermentation temperature stage called?

Diacetyl rest

What is diacetyl rest?

Stage after primary fermentation where temperature is held at a low level to encourage yeast to reabsorb diacetyl produced in fermentation

This step is important when creating a clean style beer

What is maturation monitored by?

By measurement of declining VDKs ( vicinal diketones) and precursors

Holding beer for in short term cold storage (typically up to 1 - 2 weeks) at 2 to 4 C allows yeast to what?

Permit yeast to scavenge O2 incorporated during transfer, allow formation of chill haze particles for removal by subsequent filtration, allow time for yeast sedimentation

What methods of clarification used in brewing?

• Sedimentation and centrifugation

• Filtration

• Fining agents - related to beer stability

What methods are used in beer filtration?

Dead end filtration - batch process

Or

Cross flow filtration - enables continuous operation and filtration

In beer stability what should be considered?

Microbiological, physical and flavour

In the biological stability of beer what methods can be used?

Good hygiene and sanitation practices, sterile filtration or pasteurisation

What is involved in the pasteurisation of beer?

• Thermal inactivation of microorganisms

• Flash heat treatment

• 1 pasteurisation unit (PU) = 1 minute at 60C

• Brewers typically operate at 5-15 PU

What is to be managed in the physical stability of beer? And their treatments?

• Colloidal haze

• Chill haze (redissolves after warming, treatment = filtration after cold storage) vs permanent haze (does not redissolve after warming, treatment = filtration after cold storage)

• Haze components:

  • proteinaceous (bentonite, silica gels are used as adsorbents; tannic acid precipitates proteins)

  • Polyphenols - tannins (removal - adsorbents pvpp)

  • Metal ions

  • Polysaccharides

What fining agents are commonly used?

• Carrageenan - Irish moss, whirlfloc

• Silicates

• Natural clays - bentonite

• Polyamides - nylon PVPP

• Isinglass and gelatin

For flavour stability what are the methods or processes behind this?

• Chemical oxidation leads to stale beer flavour

• Generally attributed to oxidation of higher alcohols to aldehydes by melanoidins

• Yeast - oxygen scavenger

• Flavour stability enhanced by minimising O2 pickup during finishing processes once yeasts is removed

• Antioxidants - SO2, ascorbic acid can be used

• Package container type and closure - O2 transfer rate