15.2 Stabilisation Flashcards
To what does the term ‘stabilisation’ refer?
Several winemaking interventions which, if not carried out, could lead to undesired effects in the finished wine
What is the key procedure to ensuring protein stability?
Fining with bentonite
What are tartrates? What do they consist of?
- harmless deposits of crystals that can form in the finished wine
- principally potassium bitartrate
- less frequently, calcium tartrate
How are tartrates perceived?
- many customers will regard these crystals as a fault
- thus, all high-volume winemaking and many smaller scale operations will seek to prevent this from happening
What are the 6 main options for ensuring tartrate stability?
- Cold stabilisation
- Contact process
- Electrodialysis
- Ion exchange
- Carboxymethylcellulose (CMC)
- Metatartaric acid
What is cold stabilisation? How was it performed traditional and how is it done today?
- Tartrates are less soluble at cold temperatures
- Traditionally, wine kept in a cold cellar for months through the winter
- Now, wine held at -4°C (25°F) for ~8 days so that the crystals form before bottling and can then be filtered
What are the costs associated with cold stabilisation?
- requires equipment
- energy to refrigerate the wine
What must happen before cold stabilisation?
- Colloids must be removed by fining
- They could prevent the crystals from forming at this stage
What types of tartrate does cold stabilisation treat? What does it not treat?
- only removes the more common potassium bitartrate
- does not remove calcium tartrate
What is the contact process? What are the benefits?
- a quicker, continuous, more reliable, and cheaper form of cold stabilisation
- potassium bitartrate is added to the wine
- speeds up the start of the crystallisation process
- wine cooled to around 0°C (32°F)
- after 1-2 hours the resulting crystals filtered out
What is electrodialysis?
- method of tartrate stabilization that uses a charged membrane to remove selected ions
- removes both potassium and calcium ions and, to a smaller extent, tartrate ions
What are the costs associated with electrodialysis? What are the benefits?
- high initial investment
- total costs are lower than cold stabilisation and the process uses less energy and is faster
What is ion exchange?
- does not remove tartrates
- replaces potassium and calcium ions with hydrogen or sodium ions, which will not drop out of solution
Why is ion exchange not permitted in some winemaking regions?
It replaces the potassium with sodium, which is not conducive to health
What is carboxymethylcellulose?
- CMC
- cellulose is extracted from wood
- prevents tartrates from developing to a visible size
On what types of wines is carboxymethylcellulose typically used? Why?
- Typically used for: inexpensive white and rosé wines
- Not suitable for: red wines (reacts with tannins (rendering it ineffective) and causes haze)
What are the costs associated with carboxymethylcellulose? For how long can it keep a wine stable?
- much cheaper than chilling
- keeps wines stable for a few years
What is metatartaric acid?
- when added to wines, it prevents the growth of potassium bitartrate and calcium tartrate crystals
- reduces need for cold stabilisation
On what types of wines is metatartaric acid typically used?
- red wines
What are the benefits associated with using metatartaric acid?
- quick and easy process
What are the disadvantages associated with using metatartaric acid?
- the compound is unstable
- its positive effect is lost over time, especially when wine is stored at high temperatures (25–30°C / 77–86°F)
What types of wines have the potential to re-ferment in bottle?
- Wines with residual sugar
How can a winemaker limit the potential for wines to re-ferment in bottle?
- Removing yeast through sterile filtration
- Add sorbic acid and SO2, which inhibits yeast from growing
What are the downsides of adding sorbic acid to wines to prevent re-fermentation?
- People can smell the effects of sorbic acid at very low levels
What microbes can live in wines with low pH and high alcohol?
- lactic acid bacteria
- Brettanomyces (a spoilage yeast)
What wines are at risk for malolactic conversion starting up again in bottle?
Wines with lactic acid bacteria where malolactic conversion has not been carried out or completed
Why would malolactic conversion starting up again in bottle be detrimental to the wine?
Would result in cloudiness in the bottle
What are the ways to ensure malolactic conversion does not start up again in bottle?
- ensure that malolactic conversion has been completed
2. filtering the wine to remove the bacteria
How can Brett be treated?
- Wine can be treated with DMDC (dimethyl dicarbonate, commercial name: Velcorin) before bottling, which inactivates Brettanomyces
