Post-Fermentation Clarification & Stabilisation Flashcards
Define Sedimentation:
- Natural process of clarification with suspended matter precipitating over time. (particles with higher density than wine will form a sediment at the bottom of the container
- The wine can then be racked off, leaving the sediment behind
- The number of rackings required depends on shape of the container, the volume of wine and the available labour
Define Centrifugation:
- Rapid process that spins the wine at high speed to clarify it
- Used in high-volume wineries to replace depth filtration
Define Fining
- Fining removes a small proportion of unstable colloids (microscopic particles too small to be removed by filtering) from the wine
- By adding a fining agent that speed up the process of precipitation of suspended material in the wine
- Can be of protein or mineral origin
- Must have the opposite charge from the wine colloid to be removed, forming a solid large enough to be filtered or racked
- Helps to clarify the wine and to stabilise it against the formation of hazes later in the bottle
- Can remove desirable compounds from wine or make the wine unstable when too much is added (over-fining) and therefore it is important to do trials before and add only the minimum effective amount.
- Can also help with the removal of harsh tannins in red wines or browning in white wines
Three categories of fining agents:
1. remove unstable proteins
2. remove phenolics that contribute undesirable colour and bitterness
3. remove colour and off-odours
Fining agents that removes unstable proteins:
- not necessary to remove these in red wines as they bind with tannins, precipitate naturally and are removed when the wine is racked.
- In white and rosé wines can agglomerate into a visible haze if warmed up (e.g. in transit).
Bentonite – A form of clay that adsorbs unstable proteins and unstable colloidal colouring matter.
- minimal effect on the flavour and texture of wine
- some colour loss in red wines and produces large amounts of sediment (some wine is lost at racking)
Fining agents that remove Phenolics that Contribute Undesirable Colour and Bitterness:
Egg white - Fresh or powdered form.
Used for high quality red wines to remove harsh tannins and clarify wine.
It is gentle to the wine.
Must be declared on the label (allergen)
Not suitable for vegan wines.
Gelatine – A protein collagen extracted from pork
Aids clarification, removes bitterness and astringency in red wine and browning in white wine pressings.
Easy to over-fine, stripping flavour and character, and creating the risk of a protein haze forming later
Not suitable for vegetarian or vegan
Can be used to fine must as well as wine.
Casein – A milk-derived protein
Removes browning from white wines and clarifies wines to some extent.
Must be declared as an allergen on the label
Not suitable for vegans
Can also be used to fine must as well as wine.
**Isinglass **– A protein collagen that very effectively clarifies white wines, giving them a bright appearance.
The smallest effective amount must be added to avoid potential for the formation of a protein haze later and the creation of a fishy smell.
Not suitable for vegetarian or vegan (derived from fish bladders)
Vegetable protein products – derived from potato or legumes and are suitable for vegetarian and vegan wines.
PVPP – Polyvinylpolypyrrolidone is an insoluble plastic in powder form that removes browning and astringency from oxidised white wine.
Gentler fining agent than charcoal. It is rarely used on red wines, but can reduce astringency and brighten the colour.
Fining Agent that Removes Colour and Off-Odours:
Charcoal – This removes brown colours and some off-odours.
Over-fines easily removing desirable aromas and flavours.
One option is to treat only one batch of the affected wine and then blend it with the rest of the wine to reduce this effect.
2 main type of filtration:
- Depth filtration
- Surface filtration
Depth Filtration:
Traps particles in the depth of the material that forms the filter
Can cope with fluid with many particles in it (wine that has just been pressed or lees)
Does not block easily
Not an absolute filter (some particles may pass through)
Diatomaceous earth – The most common form of depth filtration uses diatomaceous earth (‘DE’, also known as Kieselguhr), which, once it has been processed, is pure silica and inert.
The DE is wetted and used as a filter medium. Wine is sucked by vacuum from the outside of a rotary drum, through the DE, to the inside of the drum.
Used to filter very thick and cloudy wine (e.g. wine mixed with lees).
Oxidative process as the drum is exposed to air. Enclosed DE filters = can be flushed with an inert gas (e.g. nitrogen) to avoid oxidation
DE comes in a range of particle sizes and thus can remove large or very small (e.g. yeast) particles.
Initial investment in machinery is an important consideration with DE, though the per litre cost after that is small. Used DE must be disposed of responsibly, which adds an additional cost.
Sheet filters - These are also known as ‘plate and frame’ or ‘pad’ filters. The wine is passed through a sheet of the filtering material.
Very fine graded sheets can be used to remove any remaining yeasts at bottling.
Initial investment, then sheets are cheap.
Surface Filtration:
A surface filter stops particles that are bigger than the pore size of the filter from going through.
Absolute filters.
**Membrane filters **: (also called cartridge filters)
Catch particles that will not go through the pore size of the filter (pores are smaller, often less than 1 micron)
Wine must be pre-filtered first (e.g. by depth filtration) as, otherwise, membrane filters can easily get blocked.
Usually used as a final precaution immediately before the wine is bottled to ensure that the wine is completely clear and microbiologically stable (sometimes called sterile filtering = removal of yeast and bacteria)
**Cross-flow filters **– (also known as tangential filters)
They 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.
There are no replacement sheets, cartridges or earth to buy or dispose of.
Machines are expensive = more suitable for large and/or well- funded wineries.
Define Stabilisation:
Winemaking interventions which, if not carried out, could lead to undesired effects in the finished wine:
- Tackling the potential for unwanted hazes deposits in the bottle and rapid changes in the wine (browning).
- Tartrate stability
- Protein stability
- Microbiological stability
How is Protein stability ensured?
Fining with bentonite
Define Tartrates:
Principally potassium bitartrate and, less frequently, calcium tartrate, are harmless deposits of crystals that can form in the finished wine
Tartrate stabilisation:
Cold stabilisation:
- Wine held at –4°C (25°F) for around eight days so that the crystals form before bottling ( tartrates are less soluble at cold temperatures)
- Requires the equipment and the cost of energy
- Colloids must be removed by fining before this process as they could prevent the crystals from forming at this stage.
- Only removes potassium bitartrate, not calcium tartrate.
Contact process:
- Potassium bitartrate is added to the wine and speeds up the start of the crystallisation process.
- Wine is usually cooled to around 0°C (32°F) and after one or two hours the resulting crystals are filtered out.
- Quicker, continuous, more reliable and cheaper form of cold stabilisation.
Electrodialysis
- This process uses a charged membrane to remove selected ions (both potassium and calcium ions and, to a smaller extent, tartrate ions)
Ion Exchange
This process does not remove tartrates, but, instead, it replaces potassium and calcium ions with hydrogen or sodium ions, which will not drop out of solution
Carboxymethylcellulose (CmC)
- This cellulose is extracted from wood and prevents tartrates from developing to a visible size.
- Not suitable for red wines as it reacts with tannins (rendering it ineffective) and causes haze.
- Much cheaper than chilling.
- Keeps wines stable for a few years.
Metatartaric Acid
- Adding this compound prevents the growth of potassium bitartrate and calcium tartrate crystals, reducing the need for cold stabilisation. (The compound is unstable, and its positive effect is lost over time = best used for wines designed for early consumption)
- It is a quick and easy process that tends to be used more for red wines as for white wines
- CMC is more effective and long-lasting.
Microbiological stability:
- Wines with residual sugar are potentially liable to start to re-ferment in the bottle. This can be dealt with by removing yeast through sterile filtration.
- The alternative is to add sorbic acid and SO2 (inhibits yeast from growing)
Very few microbes can live in wine with low pH and high alcohol levels
- lactic acid bacteria (malolactic conversion might start up again in the bottle resulting in cloudiness: ensure MALO has been completed or filter)
- acetic acid bacteria
- Brettanomyces (a spoilage yeast): wine can be treated by filtering or with DMDC (dimethyl dicarbonate, commercial name: Velcorin) before bottling, which inactivates Brettanomyces
Finishing options:
Adjusting S02 levels
Both the total SO2 and the free SO2 are measured:
amounts of free SO2 are:
* white wine – 25–45 mg/L (lower than for red wines due to lower pH)
* red wine – 30–55 mg/L
* sweet wine – 30–60 mg/L
REDUCING DISSOLVED OXYGEN
Can accelerate the speed of ageing = reduce its shelf life.
Can be removed by flushing the wine with an inert gas to remove it, a process called sparging
ADDING CARBON DIOXIDE
Tiny bit of spritz from CO2 in the bottled wine for added freshness (for youthful white and rose)
