15.1 Post-Fermentation Clarification

Question 1

What is clarification?

Answer 1

Includes all the processes, physical and chemical, that are used to make wine clear

Question 2

What is sedimentation?

Answer 2

• suspended matter precipitating in a wine over time
• wine is allowed to stand and the particles with higher density than wine will form a sediment at the bottom of the container
• wine then be racked off, leaving the sediment behind

Question 3

When will sedimentation happen naturally?

Answer 3

• when wine is stored in cool cellar conditions

- if a wine is barrel aged

Question 4

How many rackings are typically required?

Answer 4

• depends on the size of the containers being used and the available labour
• larger vessels = greater number of rackings required to avoid a thick layer of sediment

Question 5

What are the benefits of sedimentation?

Answer 5

• 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

Question 6

What types of wines is sedimentation used for? Why?

Answer 6

• usually only suitable for premium or super-premium priced wines
• takes time

Question 7

Name 3 ways a winemaker can accelerate the clarification process.

Answer 7

1. Centrifugation
2. Fining
3. Filtering

Question 8

What is centrifugation?

Answer 8

• a rapid process that spins the wine at high rotational speed to clarify it
• can replace depth filtration and allow early bottling

Question 9

What types of wines is centrifugation effective with?

Answer 9

• wines with a lot of matter in suspension

Question 10

What styles of wines is centrifugation typically used for?

Answer 10

• high-volume wineries to spread the considerable cost of buying the machine

Question 11

What is fining? Name 3 effects fining has on a wine.

Answer 11

A procedure in which a fining agent is added to speed up the process of the precipitation of suspended material in the wine

1. removes a small proportion of unstable colloids
2. clarifies
3. stabilises against the formation of hazes later in the bottle

Question 12

Of what origin can fining agents be?

Answer 12

• protein or mineral origin

Question 13

What are colloids?

Answer 13

• microscopic particles too small to be removed by filtering

Question 14

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

Answer 14

• conduct laboratory trials before using fining agents to ensure that the minimum effective amount is used
• compare the fined sample with the original wine before proceeding

Question 15

Why is it important to not over-fine, and to only add the minimum effective amount?

Answer 15

• can remove positive compounds from wine

- can make the wine unstable when too much is added

Question 16

When choosing a fining agent, what factors are taken into consideration?

Answer 16

• 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

Question 17

Describe how fining works.

Answer 17

• 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 18

What are the 3 categories of fining agents?

Answer 18

1. those that remove unstable proteins
2. those that remove phenolics that contribute undesirable colour and bitterness
3. those that remove colour and off-odours

Question 19

Why is it important to remove grape-derived proteins from white and rose wines? Why is it less important with red wines?

Answer 19

• White: grape-derived proteins can agglomerate into a visible haze if warmed up (e.g. in transit) = a fault
• Red: grape-derived proteins bind with tannins, precipitate naturally and are removed when the wine is racked

Question 20

How are wines with grape-derived proteins fined?

Answer 20

With Bentonite

Question 21

What is bentonite?

Answer 21

A form of clay which adsorbs unstable proteins and unstable colloidal colouring matter

Question 22

What is the effect of bentonite on the final wine?

Answer 22

• 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 23

Name 6 fining agents that remove phenolics that contribute undesirable colour and bitterness in wine.

Answer 23

1. egg whites
2. gelatin
3. casein
4. insinglass
5. vegetable protein products
6. PVPP

Question 24

In what form are egg whites used to fine wines?

Answer 24

fresh or powdered form

Question 25

For what types of wines are egg whites typically used as a fining agent? Why?

Answer 25

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

Question 26

Why must egg whites be declared on a label if used in the EU?

Answer 26

- it's an allergen

Question 27

What is gelatin?

Answer 27

- A protein collagen extracted from pork

Question 28

What effect does gelatin have as a fining agent?

Answer 28

- aids clarification - removes bitterness and astringency in red wine - removes browning in white wine pressings

Question 29

Why must one be careful when fining with gelatin?

Answer 29

- must be added in the smallest effective amount - easy to over-fine with gelatin - stripping flavour and character - creating the risk of a protein haze forming later - not suitable for vegetarian wine as it is derived from animals

Question 30

What is casein?

Answer 30

- A milk-derived protein

Question 31

What effect does casein have as a fining agent?

Answer 31

- removes browning from white wines | - clarifies wines to some extent

Question 32

What is isinglass?

Answer 32

- A protein collagen that very effectively clarifies white wines, giving them a bright appearance - derived from fish bladders

Question 33

Why must one be careful when fining with isinglass?

Answer 33

- smallest effective amount must be added - potential for the formation of a protein haze later - the creation of a fishy smell - not suitable for vegetarians as it is derived from fish bladders

Question 34

What are vegetable protein products?

Answer 34

- fining agents derived from potato or legumes | - suitable for vegan-friendly wines

Question 35

What is PVPP?

Answer 35

- Polyvinylpolypyrrolidone - insoluble plastic in powder form - removes browning and astringency from oxidised white wine - gentler than charcoal

Question 36

What types of wines is PVPP used on? Rarely used on?

Answer 36

- oxidised white wine | - rarely used on red wines (but can reduce astringency and brighten the colour)

Question 37

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

Answer 37

Charcoal

Question 38

What does charcoal do?

Answer 38

- removes brown colours (e.g. to create Pale Cream Sherry) | - removes some off-odours

Question 39

Why must one be careful when fining with charcoal? What solution can be used?

Answer 39

- over-fines easily removing desirable aromas and flavours | - Solution: only one batch of the affected wine and then blend it with the rest of the wine to reduce this effect.

Question 40

What is filtration?

Answer 40

A physical separation technique used to eliminate solids from a suspension by passing it through a filter medium consisting of porous layers that trap solid particles, thus making the liquid clear

Question 41

What is the most common way of clarifying wine?

Answer 41

Filtration

Question 42

What are the two types of filtration?

Answer 42

1. depth filtration | 2. surface filtration

Question 43

What is depth filtration?

Answer 43

- traps particles in the depth of the material that forms the filter - can cope with fluid with many particles in it (e.g. wine that has just been pressed or lees) - small particles are trapped within the many irregular channels through the filter

Question 44

Why is depth filtration not always reliable?

Answer 44

- if too much pressure is applied or if the filter is used for too long, some particles will make their way through the filter - not an absolute filter

Question 45

What is the most common form of depth filtration?

Answer 45

Diatomaceous earth

Question 46

What is diatomaceous earth?

Answer 46

- form of depth filtration - once processed, is pure silica and inert - aka 'DE', 'Kieselguhr'

Question 47

What type of filter uses diatomaceous earth to filter wines in an oxidative way?

Answer 47

- Rotary vacuum filters use this method to filter very thick and cloudy wine (e.g. wine mixed with lees) - oxidative process (drum is exposed to air)

Question 48

What type of filter uses diatomaceous earth to filter wines in a non-oxidative way?

Answer 48

- Enclosed DE filters do the same job | - Can be flushed with an inert gas (e.g. nitrogen) to avoid oxidation

Question 49

How is DE flexible?

Answer 49

DE comes in a range of particle sizes and thus can remove large or very small (e.g. yeast) particles

Question 50

What happens with used DE?

Answer 50

- must be disposed of responsibly | - adds an additional cost

Question 51

What are sheet filters? Name 2 synonyms for sheet filters.

Answer 51

- aka ‘plate and frame’ or ‘pad’ filters - wine is passed through a sheet of the filtering material - the more sheets in the filter, the quicker the wine can be filtered because any portion of wine only passes through one sheet

Question 52

At bottling, how can remaining yeasts be removed?

Answer 52

Filtering with very fine graded sheets

Question 53

What are the costs associated with sheet filter systems?

Answer 53

- require investment initially (the frame must be very robust to withstand the pressures involved) - cost of filter sheets is low - trained personnel must operate them to work properly

Question 54

What are the 2 types of depth filtration?

Answer 54

1. diatomaceous earth | 2. sheet filters

Question 55

What are the 2 types of surface filtration?

Answer 55

1. membrane filters | 2. cross-flow filters

Question 56

What is a surface filter?

Answer 56

- stops particles that are bigger than the pore size of the filter from going through - absolute filters

Question 57

Which filters are absolute: depth or surface filters?

Answer 57

Surface filters

Question 58

What is a membrane filter? What's another name for membrane filter?

Answer 58

- aka 'cartridge filter' | - catch particles that will not go through the pore size of the filter

Question 59

What is slower: membrane filters or depth filters? Why?

Answer 59

- membrane filters | - the pores are smaller

Question 60

What must happen before a membrane filter is used? Why?

Answer 60

- wine must be pre-filtered first (e.g. by depth filtration) | - otherwise, membrane filters can easily get blocked

Question 61

When are membrane filters typically used?

Answer 61

- as a final precaution immediately before the wine is bottled to ensure that the wine is completely clear and microbiologically stable

Question 62

What does the term 'sterile filtering' refer to?

Answer 62

When membrane filters are used as a final precaution immediately before the wine is bottled to ensure that the wine is completely clear and microbiologically stable - not entirely accurate - the point is that yeasts and bacteria have been removed and therefore the wine is microbiologically stable

Question 63

What are the costs associated with a membrane filter?

Answer 63

- initial investment is small | - cartridges are expensive

Question 64

What is a cross-flow filter? What is another name for cross-flow filter?

Answer 64

- aka 'tangential filter' - allow 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

Question 65

What are the costs associated with a cross-flow filter?

Answer 65

- the machines are expensive, making them more suitable for large and or well-funded wineries - no replacement sheets, cartridges or earth to buy or dispose of

Question 66

What are the downsides of filtering? Why is it a controversial winemaking technique?

Answer 66

- Some believe that it can negatively affect a wine’s character, especially stripping it of texture - Others believe 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 - the fruit and the terroir may express themselves better in a correctly fined and filtered wine