15.1 Post-Fermentation Clarification Flashcards
1
Q
What is clarification?
A
Includes all the processes, physical and chemical, that are used to make wine clear
2
Q
What is sedimentation?
A
- 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
3
Q
When will sedimentation happen naturally?
A
- when wine is stored in cool cellar conditions
- if a wine is barrel aged
4
Q
How many rackings are typically required?
A
- 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
5
Q
What are the benefits of sedimentation?
A
- 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
6
Q
What types of wines is sedimentation used for? Why?
A
- usually only suitable for premium or super-premium priced wines
- takes time
7
Q
Name 3 ways a winemaker can accelerate the clarification process.
A
- Centrifugation
- Fining
- Filtering
8
Q
What is centrifugation?
A
- a rapid process that spins the wine at high rotational speed to clarify it
- can replace depth filtration and allow early bottling
9
Q
What types of wines is centrifugation effective with?
A
- wines with a lot of matter in suspension
10
Q
What styles of wines is centrifugation typically used for?
A
- high-volume wineries to spread the considerable cost of buying the machine
11
Q
What is fining? Name 3 effects fining has on a wine.
A
A procedure in which a fining agent is added to speed up the process of the precipitation of suspended material in the wine
- removes a small proportion of unstable colloids
- clarifies
- stabilises against the formation of hazes later in the bottle
12
Q
Of what origin can fining agents be?
A
- protein or mineral origin
13
Q
What are colloids?
A
- microscopic particles too small to be removed by filtering
14
Q
How do winemakers determine how much of a fining agent is used?
A
- 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
15
Q
Why is it important to not over-fine, and to only add the minimum effective amount?
A
- can remove positive compounds from wine
- can make the wine unstable when too much is added
16
Q
When choosing a fining agent, what factors are taken into consideration?
A
- 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
17
Q
Describe how fining works.
A
- 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
18
Q
What are the 3 categories of fining agents?
A
- those that remove unstable proteins
- those that remove phenolics that contribute undesirable colour and bitterness
- those that remove colour and off-odours
19
Q
Why is it important to remove grape-derived proteins from white and rose wines? Why is it less important with red wines?
A
- 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
20
Q
How are wines with grape-derived proteins fined?
A
With Bentonite
21
Q
What is bentonite?
A
A form of clay which adsorbs unstable proteins and unstable colloidal colouring matter
22
Q
What is the effect of bentonite on the final wine?
A
- 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)
23
Q
Name 6 fining agents that remove phenolics that contribute undesirable colour and bitterness in wine.
A
- egg whites
- gelatin
- casein
- insinglass
- vegetable protein products
- PVPP
24
Q
In what form are egg whites used to fine wines?
A
fresh or powdered form
25
For what types of wines are egg whites typically used as a fining agent? Why?
- high-quality red wines
- ability to remove harsh tannins and clarify wine
- gentle
26
Why must egg whites be declared on a label if used in the EU?
- it's an allergen
27
What is gelatin?
- A protein collagen extracted from pork
28
What effect does gelatin have as a fining agent?
- aids clarification
- removes bitterness and astringency in red wine
- removes browning in white wine pressings
29
Why must one be careful when fining with gelatin?
- 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
30
What is casein?
- A milk-derived protein
31
What effect does casein have as a fining agent?
- removes browning from white wines
| - clarifies wines to some extent
32
What is isinglass?
- A protein collagen that very effectively clarifies white wines, giving them a bright appearance
- derived from fish bladders
33
Why must one be careful when fining with isinglass?
- 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
34
What are vegetable protein products?
- fining agents derived from potato or legumes
| - suitable for vegan-friendly wines
35
What is PVPP?
- Polyvinylpolypyrrolidone
- insoluble plastic in powder form
- removes browning and astringency from oxidised white wine
- gentler than charcoal
36
What types of wines is PVPP used on? Rarely used on?
- oxidised white wine
| - rarely used on red wines (but can reduce astringency and brighten the colour)
37
Name a fining agent that removes colour and off-odours.
Charcoal
38
What does charcoal do?
- removes brown colours (e.g. to create Pale Cream Sherry)
| - removes some off-odours
39
Why must one be careful when fining with charcoal? What solution can be used?
- 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.
40
What is filtration?
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
41
What is the most common way of clarifying wine?
Filtration
42
What are the two types of filtration?
1. depth filtration
| 2. surface filtration
43
What is depth filtration?
- 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
44
Why is depth filtration not always reliable?
- 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
45
What is the most common form of depth filtration?
Diatomaceous earth
46
What is diatomaceous earth?
- form of depth filtration
- once processed, is pure silica and inert
- aka 'DE', 'Kieselguhr'
47
What type of filter uses diatomaceous earth to filter wines in an oxidative way?
- 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)
48
What type of filter uses diatomaceous earth to filter wines in a non-oxidative way?
- Enclosed DE filters do the same job
| - Can be flushed with an inert gas (e.g. nitrogen) to avoid oxidation
49
How is DE flexible?
DE comes in a range of particle sizes and thus can remove large or very small (e.g. yeast) particles
50
What happens with used DE?
- must be disposed of responsibly
| - adds an additional cost
51
What are sheet filters? Name 2 synonyms for sheet filters.
- 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
52
At bottling, how can remaining yeasts be removed?
Filtering with very fine graded sheets
53
What are the costs associated with sheet filter systems?
- 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
54
What are the 2 types of depth filtration?
1. diatomaceous earth
| 2. sheet filters
55
What are the 2 types of surface filtration?
1. membrane filters
| 2. cross-flow filters
56
What is a surface filter?
- stops particles that are bigger than the pore size of the filter from going through
- absolute filters
57
Which filters are absolute: depth or surface filters?
Surface filters
58
What is a membrane filter? What's another name for membrane filter?
- aka 'cartridge filter'
| - catch particles that will not go through the pore size of the filter
59
What is slower: membrane filters or depth filters? Why?
- membrane filters
| - the pores are smaller
60
What must happen before a membrane filter is used? Why?
- wine must be pre-filtered first (e.g. by depth filtration)
| - otherwise, membrane filters can easily get blocked
61
When are membrane filters typically used?
- as a final precaution immediately before the wine is bottled to ensure that the wine is completely clear and microbiologically stable
62
What does the term 'sterile filtering' refer to?
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
63
What are the costs associated with a membrane filter?
- initial investment is small
| - cartridges are expensive
64
What is a cross-flow filter? What is another name for cross-flow filter?
- 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
65
What are the costs associated with a cross-flow filter?
- 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
66
What are the downsides of filtering? Why is it a controversial winemaking technique?
- 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
