15.1 Post-Fermentation Clarification

Question 1

What is clarification?

Answer 1

• physical and chemical processes used to make wine clear :
  
  • sedimentation (time consuming)
• faster methods:
  
  • centrifugation
  • fining
  • filtration

Question 2

What is sedimentation?

Answer 2

particles with higher density than wine collect naturally at the bottom of the container

• when wine is stored in cool cellar conditions
• if a wine is barrel aged
• wine then needs tb racked off, leaving the sediment behind (may need to be repeated depends on the size of the containers being

Benefit

• clarification by sedimentation avoids the potential loss of texture and flavour that may occur if the wine is fined or filtered
• some premium wines are clarified only in this way
• this method is only used on prem or super prem wines due to the length of time taken

Question 3

What is centrifugation?

Answer 3

Rapid process that spins the wine at high rotational speed to clarify it

• can replace depth filtration and allow early bottling

Effective for

• wines with a lot of matter in suspension

Used for high-volume wineries (justify the cost)

Question 4

What is fining?

Answer 4

Procedure in which a fining agent is added to speed up the process of sedimentation.

Different types of fining agents do different things

Removing unstable proteins: Bentonite*

Removing phenolics (undesirable colours / bitterness):

egg white, gelatine*, casein*, isinglass, vegetal protein, pvpp

Removing colour and off odours: charcoal

Some fining agents can only be used on must.

Other fining agents can be used on must and wine*.

Caution - fining agents:

• can remove positive compounds from wine
• can make the wine unstable when too much is added

Question 5

What types of fining are there, and

Answer 5

• protein or mineral origin colloid = - microscopic particles too small to be removed by filtering - each fining agent has particular properties that can offer solutions to problems (e.g. removal of harsh tannins in red wines, browning in white wines) - fining agent must have the opposite charge from the wine colloid to be removed - fining agent and the colloid attract each other - form a solid large enough (sink to bottom of liquid) to be removed by racking or by filtration

Question 6

How do winemakers determine how much of a fining agent is used?

Answer 6

• laboratory trials establish min effective amount
• comparison in the winery
• adoption of agent

Question 7

Explain the use of Bentonite to remove unstable proteins

Answer 7

In white wines
grape-derived proteins can agglomerate into a visible haze if warmed up (e.g. in transit) = a fault

In red wines (bentonite not needed normally)
grape-derived proteins bind with tannins, precipitate naturally and are removed when the wine is racked

Use of bentonite

• A form of clay which adsorbs unstable proteins and unstable colloidal colouring matter
• minimal effect on the flavour and texture of wine.
• leads to some colour loss in red wines
• produces large amounts of sediment (wine is lost when racked)

Question 8

Describe the 6 fining agents that remove phenolics (undesirable colour and bitterness)

Answer 8

1. egg whites fresh or powdered form

• high-quality red wines
• ability to remove harsh tannins and clarify wine
• gentle

Caution

• must be declared on label - it’s an allergen
  2. gelatin (fines must and wine)
• A protein collagen extracted from pork
• aids clarification
• removes bitterness and astringency in red wine
• removes browning in white wine pressings

Caution!

• too much strips flavour and character & risk of protein haze later
  3. casein (fines must and wine)
• A milk-derived protein
• removes browning from white wines
• clarifies wines to some extent

4. insinglass

• clarifies white wines, giving them a bright appearance
• derived from fish bladders

Caution!

• min amount to avoid protein haze later
• the creation of a fishy smell

5. vegetable protein products

• derived from potato or legumes
• vegan-friendly

6. PVPP - insoluble plastic in powder form

• removes browning and astringency from oxidised white wine
• gentler than charcoal
• can reduce astringency and brighten the colour in red wine

Question 9

Describe a fining agent that removes colour and off-odours.

Answer 9

Charcoal

• removes brown colours (e.g. to create Pale Cream Sherry) and off odours

Caution

• easily overfines, removing desirable colours/flavours
• counteract by fining one batch, and blend it with the rest.

Question 10

Explain the use of filtration in post fermentation clarification.

Answer 10

• a physical separation technique used to eliminate solids from the wine by passing them through a filter of porous layers that trap solid particles

Two types

1. depth filtration (DE and Sheet filters)

• traps particles in the depth of the material that forms the filter
• small particles are trapped within the many irregular channels through the filter

Disadvantage

• too much pressure or if used too long, some particles get through
  2. surface filtration (membrane/ cross-flow )
• stops particles that are bigger than the pore size
• absolute filters

Question 11

Explain what DE is and how it works

Answer 11

• Diatomaceous earth-
• most common form of depth filtration
• filters very thick and cloudy wine
• Although drum is exposed to air, filters can be flushed with gas for non-oxidative process
• can remove large or very small (e.g. yeast) particles.
• must be disposed of responsibly - adds an additional cost

Question 12

Explain what sheet filters are and how it works

Answer 12

• aka “plate and frame” or pad filter
• wine is passed through a sheet of the filtering material
• The more sheets in the filter, the quicker the wine can be filtered
• Can be used at bottling to remove any remaining yeast (very fine graded sheets 0.45 micron)

Costs

• require investment initially
• cost of filter sheets is low
• trained personnel must operate them to work properly

Question 13

What are the 2 types of surface filtration?

Answer 13

1. membrane filters 2. cross-flow filters

Question 14

Explain how the membrane filter works

Answer 14

• • aka ‘cartridge filter’
• commonly used as a final precaution immediately before the wine is bottled to ensure the wine completely clear and microbiologically stable
• commonly called sterile filtering - however its not that precise, but does ensure wine is microbioligically stable
• catch particles that will not go through the pore size of the filter <1 micron
• wine must be pre-filtered first (e.g. by depth filtration)otherwise, membrane filters can easily get blocked

Costs:

• initial investment is small
• cartridges are expensive

Question 15

What is a cross-flow filter?

Answer 15

• • aka ‘tangential filter’
• allows wine to pass through the filter while uniquely cleaning the surface of the filter as it works
• solid particles cannot pass through the filter
• can filter wine with a high load of particles or lees very quickly

Costs

• the machines are expensive - suit large, well-funded wineries
• no replacement sheets, cartridges or earth to buy or dispose of.

Question 16

Controversy re filtering?

Answer 16

Some argue

it can negatively affect a wine’s character stripping it of texture

Others that any immediate loss of texture is compensated in two ways

1. wine will recover from the shock of filtration after some months
2. much less chance of wines developing faults as bacteria and yeasts have been removed

and the fruit and the terroir may express themselves better in a correctly fined and filtered wine