16.4 White Winemaking: Clarification of Must

Question 1

When is the juice of white grapes clarified?

Answer 1

• Before and after fermentation

Question 2

What is the aim for must clarification?

Answer 2

• reduce the amount of suspended solids in must to 0.5 - 2% solids

Question 3

Why might producers choose to retain higher proportions of solids in their must?

Answer 3

Some choose to stop at 1%

• add to the texture of the wine
• gives a subtle astringency
• give a greater range of aromas
• greater complexity

Question 4

For what types of wines is a lower proportions of solids in the must desirable?

Answer 4

Fresh, fruity styles

Question 5

Why do fermentations with high level of solid require careful monitoring?

Answer 5

• Various compounds within the solids and their reactions can lead to off-flavours
• e.g. reductive sulfur compounds

Question 6

Why is a small amount of solids beneficial?

Answer 6

• provides nutrients for yeast

- over-clarifying must can lead to stuck fermentations

Question 7

Why do fermentations with a very low level of solids require careful monitoring?

Answer 7

May need to add yeast nutrients (such as DAP) to avoid stuck fermentation

Question 8

Explain sedimentation?

Answer 8

Form of clarification aka ‘settling’
- simplest form of clarification used on must and wines
- suspended solids in the must are left to fall over time with gravity
Process:
Wine chilled to 4°C - ROTSO & SF
Period of 12 - 24hrs
Quicker in large flat container than tall vertical
Must/wine racked off, solids left behind may be filtered to reclaim useable juice.
Cheap process small batch process - def premium wines only

Question 9

What are the advantages & disadvantages of sedimentation?

Answer 9

Advantage
- cheapest in terms of equipment
- requires no additives
Disadvantage
- takes long
- not energy efficient (chilling)

Question 10

What is flotation?

Answer 10

• 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

Question 11

What are the advantages/disadvantages of flotation?

Answer 11

Advantages
- speeds up the rate of clarification
- continuous or batch process
- doesn't require chilling (saving on energy costs)
Disadvantage
- more expensive (equipment)

Question 12

If oxygen is used as the gas in flotation, flotation is also a method of what?

Answer 12

Hyperoxidation

Question 13

What is a centrifugation

Answer 13

• machine that uses centrifugal force to separate solids from liquids
• can be used on must and wines

Question 14

What are the advantages/disadvantages of centrifugations?

Answer 14

Advantages
-can be used on must and wine
- fast
- used continuously (not batch), saves time and labour costs
Disadvantages
- expensive (only feasible in large wineries)
- increase the must’s exposure to oxygen unless the machine is flushed with inert gas (extra cost)

Question 15

Explain the use of clarifying agents to clarify wine

Answer 15

Clarification with agents is the use of processing aids to speed up the rate of sedimentation
- can only be used in must, not wine

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

Cost associated

• purchase of agents
• may be justified against the time and energy saved compared to sedimentation (chilling)

Clarification of WINE with clarifying agents would use Bentonite, gelatine or caseine.