15.1 Post-Fermentation Clarification Flashcards
What is clarification?
Includes all the processes, physical and chemical, that are used to make wine clear
What is sedimentation?
- 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
When will sedimentation happen naturally?
- when wine is stored in cool cellar conditions
- if a wine is barrel aged
How many rackings are typically required?
- 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
What are the benefits of sedimentation?
- 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
What types of wines is sedimentation used for? Why?
- usually only suitable for premium or super-premium priced wines
- takes time
Name 3 ways a winemaker can accelerate the clarification process.
- Centrifugation
- Fining
- Filtering
What is centrifugation?
- a rapid process that spins the wine at high rotational speed to clarify it
- can replace depth filtration and allow early bottling
What types of wines is centrifugation effective with?
- wines with a lot of matter in suspension
What styles of wines is centrifugation typically used for?
- high-volume wineries to spread the considerable cost of buying the machine
What is fining? Name 3 effects fining has on a wine.
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
Of what origin can fining agents be?
- protein or mineral origin
What are colloids?
- microscopic particles too small to be removed by filtering
How do winemakers determine how much of a fining agent is used?
- 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
Why is it important to not over-fine, and to only add the minimum effective amount?
- can remove positive compounds from wine
- can make the wine unstable when too much is added
When choosing a fining agent, what factors are taken into consideration?
- 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
Describe how fining works.
- 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
What are the 3 categories of fining agents?
- those that remove unstable proteins
- those that remove phenolics that contribute undesirable colour and bitterness
- those that remove colour and off-odours
Why is it important to remove grape-derived proteins from white and rose wines? Why is it less important with red wines?
- 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
How are wines with grape-derived proteins fined?
With Bentonite
What is bentonite?
A form of clay which adsorbs unstable proteins and unstable colloidal colouring matter
What is the effect of bentonite on the final wine?
- 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)
Name 6 fining agents that remove phenolics that contribute undesirable colour and bitterness in wine.
- egg whites
- gelatin
- casein
- insinglass
- vegetable protein products
- PVPP
In what form are egg whites used to fine wines?
fresh or powdered form
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
Why must egg whites be declared on a label if used in the EU?
- it’s an allergen
What is gelatin?
- A protein collagen extracted from pork
What effect does gelatin have as a fining agent?
- aids clarification
- removes bitterness and astringency in red wine
- removes browning in white wine pressings
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
What is casein?
- A milk-derived protein
What effect does casein have as a fining agent?
- removes browning from white wines
- clarifies wines to some extent
What is isinglass?
- A protein collagen that very effectively clarifies white wines, giving them a bright appearance
- derived from fish bladders
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
What are vegetable protein products?
- fining agents derived from potato or legumes
- suitable for vegan-friendly wines
What is PVPP?
- Polyvinylpolypyrrolidone
- insoluble plastic in powder form
- removes browning and astringency from oxidised white wine
- gentler than charcoal
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)
Name a fining agent that removes colour and off-odours.
Charcoal
What does charcoal do?
- removes brown colours (e.g. to create Pale Cream Sherry)
- removes some off-odours
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.
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
What is the most common way of clarifying wine?
Filtration
What are the two types of filtration?
- depth filtration
2. surface filtration
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
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
What is the most common form of depth filtration?
Diatomaceous earth
What is diatomaceous earth?
- form of depth filtration
- once processed, is pure silica and inert
- aka ‘DE’, ‘Kieselguhr’
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)
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
How is DE flexible?
DE comes in a range of particle sizes and thus can remove large or very small (e.g. yeast) particles
What happens with used DE?
- must be disposed of responsibly
- adds an additional cost
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
At bottling, how can remaining yeasts be removed?
Filtering with very fine graded sheets
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
What are the 2 types of depth filtration?
- diatomaceous earth
2. sheet filters
What are the 2 types of surface filtration?
- membrane filters
2. cross-flow filters
What is a surface filter?
- stops particles that are bigger than the pore size of the filter from going through
- absolute filters
Which filters are absolute: depth or surface filters?
Surface filters
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
What is slower: membrane filters or depth filters? Why?
- membrane filters
- the pores are smaller
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
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
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
What are the costs associated with a membrane filter?
- initial investment is small
- cartridges are expensive
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
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
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
