Clarification, Stabilisation and Finishing Flashcards
Sedimentation
A form of clarification
If wine is stored in cool cellars conditions, the process of clarification will begin naturally. With gravity particles with higher density than the wine will form a sediment at the bottom of the container.
The wine can be racked off, leaving the sediment behind. The number of rackings required depends on the size of the container and the available labour. The larger the container, the greater the number of rankings to avoid a thick layer of sediment
Some premium wines are clarified only this way because some may believe that clarification by sedimentation avoids the potential loss of texture and flavor that may occur when a wine is fined or filtered
Sedimentation takes time, which adds to the cost as the wine can not be sold until ready to be released (premium or super premium wines) However, when wines are matured in barrel, sedimentation will happen during the maturation process
Centrifugation
A form of clarification
A rapid process that spins the wine at high rotational speed to clarify it and allows early bottling
Highly effective for wine with a lot of matter in suspension
Only practices in high volume wineries to spread the considerable cost of buying the machine
Fining
A form of clarification
A procedure in which a fining agent (protein or mineral origin) is added to speed up the process of the precipitation (neerslag) of suspended material in the wine
It removes a small proportion of unstable collide (microscopic particles too small to be removed by filtering) and help to clarify the wine and to stabilize it again the formation of hazes later in the bottle
Laboratory trials before using the fining agent ensure that the min effective amount is used, comparing the fined sample with the original wine
Fining agents can remove positive compounds from the wine or make the wine unstable if too much is added (over-fining)
In addition, each fining agent has its particular properties that can offer solutions to problems such as removal of harsh tannings or browning in white wines
The fining agent and the colloid attract each other and form a solid large enough to be removed by racking or filtration
Three categories of common fining agents are
- Those that remove unstable proteins
- Those that remove phenolics that contribute undesirable colour and bitterness
- Those that remove colour and off-aromas
Fining agents that remove unstable proteins
Must and wine contain grape-derived proteins
Not necessary to remove in red wines as they bind with tannins, precipitate naturally and are removed when the wine is racked of
Proteins in white and rose wines can agglomerate into a visible hazes if warmed up, for example during transit, which would be seen as a fault
These wines are often fined with bentonite
Bentonite
A form of clay which absorbs unstable proteins and unstable colloidal colouring matter
Min effect on flavour and texture of wine
Leads to some colour loss in red wines and produces large amount of sediment, and so wine is lost when it is racked of
Fining agents that remove phenolics that contribute undesirable colour and bitterness (6)
Egg white
Gelatin
Casein
Isinglass
Vegetable protein products
PVPP
These fining agents may be used in conjunction with bentonite for their own properties and to avoid the risk of over-fining (which could make the wine unstable)
Egg white
Often used fresh or in powdered form
High quality red wines, ability to remove hars tannins and clarify wine and is gentle
Its an alleged, must be declared on the label if soled in the EU and other territories if present above a specified limit
Gelatin
A protein collagen extracted from pork that aids clarification, removes bitterness and astringency in red wine and browning in white wine pressings
Must be added in the smaller effective amount as it is easy to overfine gelatin, stripping flavour and character and creating the risk of a protein haze forming later
Not suitable for vegetarians
Casein (kaasstof)
A milk derived protein that removes browning for white wines and clarifies wine to some extent
Must be declared as an allergen in some territories
Isinglass
Protein collagen that very effectively clarifies white wines, giving them a bright appearance
The smallest effective amount must be added to avoid potential haze later (over-fining) and the creation of a fishy smell
Not suitable for vegetarians (fish bladders)
Vegetable protein products
Derived from potato or legumes and suitable for vegan-friendly wines
PVPP
Poly-vinyl-poly-pyrrolidone is an insoluble plastic in powder form that removes browning and astringency from oxidized white wine
More gentle than charcoal
Rarely used for red wine, but can reduce astringency and brighten the colour
Fining agents that remove colour and off-aromas
Charcoal removes brown colours and some off aromas
Over fines early removing desirable aromas and flavours
Option is to treat one batch of the affected wine and than blend it with the rest of the wine to reduce this effect
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
It is the most common way of filtering a wine
Two main types;
- Depth filtration
- Surface filtration
Depth filtration
Traps particles in the depth of the material that forms the filter. It can cope with fluid with many particles in it (wine that is just pressed or lees).
Small particles are trapped within the many irregular channels thought the filter. This filter does not block easily, but it is not absolutely reliable because, if too much pressure is applied or if the filer is used for too long, some particles will make their way through the filter
It’s not an absolute filter
Diatomaceous earth
Most common form of depth filtration, by using diatomaceous earth, which once processed, is pure silica
DE is also known as Kieslguhr
Rotary vacuum filters use this method to filter very thick and cloudy wine (with lees), its an oxidative process as the drum is exposed to air
Enclosed DE filters do the same job, but can be flushed with an inert gas (nitrogen) to avoid oxidation
DE comes in a range of particle size and therefore can remove large or very small particles (yeast)
DE that is used must be disposed of responsibly, which adds to the cost
Sheet filters
Also known as plate and frame or pad filters
The wine is passed through a sheet of the filtering material. Very fine sheets can be used to remove any reaming yeasts at bottling
The more sheets, the quicker the wine can be filtered, because any portion of wine only passes through one sheet
High initial investment of the machine, although the cost of filter sheets is low. Trained staff must operate them to work properly
Surface filtration
A surface filter stops particles that are bigger than the pore size of the filter from going through
They are often termed absolute filters
There are two types:
Membrane filters
Cross-flow filters
Membrane filters
Also called cartridge filters
Catch particles that will not go through the pore size of the filter
Slower than depth filer as pores are smaller (less 1 micron), for the same reason wine must be pre-filtered first because otherwise membrane filters can easily be blocked
Generally used as final precaution immediately before bottling to ensure the wine is completely clear and microbiologically stable
In contrast to depth filters, the initial investment is small, but cartridges are expensive
Very common in bottling/packaging process
Cross-flow filters
Also called tangential filters
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, it can filter wine with a high load of particles or lees very quick
There are no replacement sheets, cartridges or earth to buy or dispose. However, the machines are expensive. More suitable to large or well-funded wineries
The impact on quality of filtering a wine
Some critics and winemakers believe that filtration negatively affect a wines character, especially stripping if of texture. Therefore, some wines are bottled unfiltered
However, others argue that immediate loss of text is compensated in two ways:
- The wine will recover from the shock of filtration after some months
- Much less chance of wines developing faults as bacteria and yeasts have been removed
The argument that the fruit and terroir express themselves better in fined and filtered wines continuous. Although there are no scientific studies to support this
Stabilisation
Refers to several winemaking interventions which, if not carried out, could lead to undesired effect in the finished wine
Including the following:
- Tackling the potential for unwanted hazes
- Deposits in the bottle and rapid changes in the wine (browning)
Protein stability
Fining with bentonite is the key procedure to ensure protein stability
Tartrate stability
Tartrates are harmless deposits of crystals that can form in the finished wine, principally formed by potassium bitartrate and less frequently by calcium tartrate
Many consumers will regard this as a fault, and many producers will seek to prevent this from happening by the following:
- Cold stabilization
- Contact process
- Electrodialysis
- Ion exchange
- CMC - Carboxymethylcellulose
- Metatartaric acid
Cold stabilization
Traditionally by keeping the wine in a cold cellar through the winter
More reliable, wine can be held at -4 four around 8 days so that the crystals form before bottling (crystals are less soluble at cold temp) and can than be filtered out
Requires equipment and cost of entry to refrigerate the wine
Colloids must be removed by fining before this process, a they could prevent the crystals from forming at this stage
Removes the more common potassium bitartrate, not calcium tartrate
Contact process
Quicker, continuous, more reliable and cheaper form of cold stabilization
Potassium bitartrate is added to the Wien and speeds up the start of they crystallization process
Wine is usually cooled below zero degrees and after one or two hours the rustling crystals are filtered out
Electrodialysis
Uses a charged membrane to remove selected ions
After high investment, the total cost is lower than cold stabilization and uses less energy and is faster
Removes both potassium as calcium ions, and to a smaller extent tartrate ions
Ion exchange
Does not include the removal of tartrates, instead, replaces potassium and calcium inons with hydrogen or sodium ions, which will not drop out of solution
Not allowed in some territories as it is replaced by sodium (which is not conducive to health). However, levels in wine are low below the legal limit
Metatartaric acid
Adding this compound prevents the growth of potassium bitartrate and calcium tartrate crystals, reducing the need for cold stabilisation
Quick and easy process
However, the compound is unstable, and its positive effect is lost over time, especially when stored at high temperatures (25-30)
CMC - Carboxymethylcellulose
This cellulose is extracted from wood and prevents tartrates from developing to a visible size
Widely used on inexpensive white and rose wines, because it keeps wines stable for a few years and its much cheaper than chilling
Not suitable for red wines, as it reacts wit tannin and cause hazes
Microbiological Stability
Wines with RS are potentially liable to start a referent in the bottle
Can be dealt with by removing yeast through sterile filtration or to add sorbic acid and so2, which inhabits yeast from growing
Very few micros can live within wine with its low pH and high alcohol levels. However, lactic acid bacteria and Brettanomyces are exceptions
Wines with lactic acid bacteria where Malo has not been carried out or completed are liable to Malo starting again in the bottle (cloudiness) this can be counted by ensuring Malo has been completed or filtering out he bacteria
If Brettanomcyes is a problem, wine can be treated with DMDC (dimethyl bicarbonate, commercially; Velcorin) before bottling, which inactivates Brettanomyces
Finishing options
Before bottling is carried out the winemaker will make a full chemical analysis measuring; alcohol, rs, free so2 and in the light of this analysis, final adjustment can be made
Adjusting the level of sulfur dioxide
Reducing dissolved oxygen
Adding carbon dioxide
Finishing - Adjusting the level of sulfur dioxide
so2 must be within legal limits
Many factors will affect the levels of so2 in wines at the point of filling, including winemaker approach, wine style, pH and the intended drinking period (early/aging)
In general the amounts of free so2 are :
- White 25-45 mg/l
- Red 30-55 mg/l
- Sweet 30-60 mg/l
Reducing dissolved oxygen
Oxygen dissolved in wine can accelerate the speed of aging of the wine and thus reduce its shelf life
If oxygen levels are found to be too high, it can be removed by flushing the wine with an inert gas to remove it, called sparging
Adding carbon dioxide
A small amount of co2 may remain in wine after finishing and packaging
Especially for inexpensive white wines, some winemakers will prefer a tiny bit of a sprit from co2 in the bottled wine for added freshness. If desired, is added just before bottling
