16.4 White Winemaking: Clarification of Must

Question 1

When is the juice of white grapes clarified?

Answer 1

• Between pressing and fermentation

- (Also post-fermentation)

Question 2

What is the aim for must clarification?

Answer 2

To reduce the amount of suspended solids within the must (solids include particles of grape skin, stem, and seeds)

Question 3

What is the ideal percentage for the proportion of solids in the must?

Answer 3

.5-2%

Question 4

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

Answer 4

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

Question 5

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

Answer 5

Fresh, fruity styles

Question 6

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

Answer 6

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

Question 7

Why is a small amount of solids beneficial?

Answer 7

• provides nutrients for yeast

- over-clarifying must can lead to stuck fermentations

Question 8

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

Answer 8

May need to add yeast nutrients (such as DAP)

Question 9

What is sedimentation?

Answer 9

• 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

Question 10

During sedimentation, to what temperature is the must generally chilled?

Answer 10

4°C (39°F)

Question 11

Why is must chilled?

Answer 11

• to reduce the rate of oxidation
• to reduce microbial spoilage
• to avoid a spontaneous fermentation

Question 12

What affect does the size and shape of the vessel have on sedimentation?

Answer 12

Sedimentation takes longer in large, tall vessels than in smaller, shorter vessels due to the depth over which the solids need to fall

Question 13

How long does sedimentation typically take?

Answer 13

12–24 hours

Question 14

What is racking?

Answer 14

When the clear juice is transferred to the fermentation vessel, leaving the sediment of solids at the bottom of the sedimentation vessel

Question 15

What happens to solids left behind after sedimentation?

Answer 15

Often filtered by cross flow or depth filters to extract extra juice

Question 16

What are the advantages of sedimentation?

Answer 16

• cheapest in terms of equipment

- requires no additives

Question 17

What are the disadvantages of sedimentation?

Answer 17

• takes long

- not energy efficient (chilling)

Question 18

For what types of wine production is sedimentation typically used?

Answer 18

Small-volume production of premium wines

Question 19

What is flotation?

Answer 19

• 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 20

What are the advantages of flotation?

Answer 20

• speeds up the rate of clarification
• continuous or batch process
• doesn’t require chilling (saving on energy costs)

Question 21

What are the disadvantages of flotation?

Answer 21

• more expensive (equipment)

Question 22

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

Answer 22

Hyperoxidation

Question 23

What is a centrifuge?

Answer 23

• machine that comprises a rapidly rotating container which uses centrifugal force to separate solids from liquids
• can be used on must and wines

Question 24

What are the advantages of centrifuges?

Answer 24

• clarify the must quickly

- used continuously (not batch), saves time and labour costs

Question 25

What are the disadvantages of centrifuges?

Answer 25

• expensive (only feabile in large wineryes)

- increase the must’s exposure to oxygen unless the machine is flushed with inert gas (extra cost)

Question 26

Why might clarifying agents be added to grape must?

Answer 26

• processing aids: speed up the rate of sedimentation

- can only be used in must, not wine

Question 27

What clarifying agent is typically added to grape must? What is its specific purpose?

Answer 27

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

Question 28

What are the cost associated with clarifying agents for grape must?

Answer 28

• purchasing these agents

- may be justified against the time and energy saved compared to sedimentation (chilling)