16.4 White Winemaking: Clarification of Must Flashcards
When is the juice of white grapes clarified?
- Between pressing and fermentation
- (Also post-fermentation)
What is the aim for must clarification?
To reduce the amount of suspended solids within the must (solids include particles of grape skin, stem, and seeds)
What is the ideal percentage for the proportion of solids in the must?
.5-2%
Why might producers choose to retain higher proportions of solids in their must?
- add to the texture of the wine
- gives a subtle astringency
- give a greater range of aromas from fermentation
- greater complexity
For what types of wines is a lower proportions of solids in the must desirable?
Fresh, fruity styles
Why do fermentations with high level of solid require careful monitoring?
- Various compounds within the solids and their reactions can lead to off-flavours (e.g. reductive sulfur compounds)
Why is a small amount of solids beneficial?
- provides nutrients for yeast
- over-clarifying must can lead to stuck fermentations
Why do fermentations with a very low level of solids require careful monitoring?
May need to add yeast nutrients (such as DAP)
What is sedimentation?
- aka ‘settling’
- simplest form of clarification (can be used on must and wines)
- suspended solids in the must are left to fall over time with gravity
During sedimentation, to what temperature is the must generally chilled?
4°C (39°F)
Why is must chilled?
- to reduce the rate of oxidation
- to reduce microbial spoilage
- to avoid a spontaneous fermentation
What affect does the size and shape of the vessel have on sedimentation?
Sedimentation takes longer in large, tall vessels than in smaller, shorter vessels due to the depth over which the solids need to fall
How long does sedimentation typically take?
12–24 hours
What is racking?
When the clear juice is transferred to the fermentation vessel, leaving the sediment of solids at the bottom of the sedimentation vessel
What happens to solids left behind after sedimentation?
Often filtered by cross flow or depth filters to extract extra juice
What are the advantages of sedimentation?
- cheapest in terms of equipment
- requires no additives
What are the disadvantages of sedimentation?
- takes long
- not energy efficient (chilling)
For what types of wine production is sedimentation typically used?
Small-volume production of premium wines
What is flotation?
- involves bubbling gas (typically nitrogen) up through the must
- as the bubbles of gas rise, they bring with them the solid particles
- solid particles are then skimmed off the top of the vessel
- can only be used on must, not wine
What are the advantages of flotation?
- speeds up the rate of clarification
- continuous or batch process
- doesn’t require chilling (saving on energy costs)
What are the disadvantages of flotation?
- more expensive (equipment)
If oxygen is used as the gas in flotation, flotation is also a method of what?
Hyperoxidation
What is a centrifuge?
- machine that comprises a rapidly rotating container which uses centrifugal force to separate solids from liquids
- can be used on must and wines
What are the advantages of centrifuges?
- clarify the must quickly
- used continuously (not batch), saves time and labour costs
What are the disadvantages of centrifuges?
- expensive (only feabile in large wineryes)
- increase the must’s exposure to oxygen unless the machine is flushed with inert gas (extra cost)
Why might clarifying agents be added to grape must?
- processing aids: speed up the rate of sedimentation
- can only be used in must, not wine
What clarifying agent is typically added to grape must? What is its specific purpose?
Pectolytic enzymes
- break down pectins in the must
- pectins are naturally found in plant cell walls
- allows a more rapid separation between the liquid juice and solids
What are the cost associated with clarifying agents for grape must?
- purchasing these agents
- may be justified against the time and energy saved compared to sedimentation (chilling)
