15.2 Stabilisation

Question 1

To what does the term ‘stabilisation’ refer?

Answer 1

Several winemaking interventions which, if not carried out, could lead to undesired effects in the finished wine

Question 2

What is the key procedure to ensuring protein stability?

Answer 2

Fining with bentonite

Question 3

What are tartrates? What do they consist of?

Answer 3

• harmless deposits of crystals that can form in the finished wine
• principally potassium bitartrate
• less frequently, calcium tartrate

Question 4

How are tartrates perceived?

Answer 4

• 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

Question 5

What are the 6 main options for ensuring tartrate stability?

Answer 5

1. Cold stabilisation
2. Contact process
3. Electrodialysis
4. Ion exchange
5. Carboxymethylcellulose (CMC)
6. Metatartaric acid

Question 6

What is cold stabilisation? How was it performed traditional and how is it done today?

Answer 6

• 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

Question 7

What are the costs associated with cold stabilisation?

Answer 7

• requires equipment

- energy to refrigerate the wine

Question 8

What must happen before cold stabilisation?

Answer 8

• Colloids must be removed by fining

- They could prevent the crystals from forming at this stage

Question 9

What types of tartrate does cold stabilisation treat? What does it not treat?

Answer 9

• only removes the more common potassium bitartrate

- does not remove calcium tartrate

Question 10

What is the contact process? What are the benefits?

Answer 10

• 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

Question 11

What is electrodialysis?

Answer 11

• 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

Question 12

What are the costs associated with electrodialysis? What are the benefits?

Answer 12

• high initial investment

- total costs are lower than cold stabilisation and the process uses less energy and is faster

Question 13

What is ion exchange?

Answer 13

• does not remove tartrates

- replaces potassium and calcium ions with hydrogen or sodium ions, which will not drop out of solution

Question 14

Why is ion exchange not permitted in some winemaking regions?

Answer 14

It replaces the potassium with sodium, which is not conducive to health

Question 15

What is carboxymethylcellulose?

Answer 15

• CMC
• cellulose is extracted from wood
• prevents tartrates from developing to a visible size

Question 16

On what types of wines is carboxymethylcellulose typically used? Why?

Answer 16

• Typically used for: inexpensive white and rosé wines

- Not suitable for: red wines (reacts with tannins (rendering it ineffective) and causes haze)

Question 17

What are the costs associated with carboxymethylcellulose? For how long can it keep a wine stable?

Answer 17

• much cheaper than chilling

- keeps wines stable for a few years

Question 18

What is metatartaric acid?

Answer 18

• when added to wines, it prevents the growth of potassium bitartrate and calcium tartrate crystals
• reduces need for cold stabilisation

Question 19

On what types of wines is metatartaric acid typically used?

Answer 19

• red wines

Question 20

What are the benefits associated with using metatartaric acid?

Answer 20

• quick and easy process

Question 21

What are the disadvantages associated with using metatartaric acid?

Answer 21

• 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)

Question 22

What types of wines have the potential to re-ferment in bottle?

Answer 22

• Wines with residual sugar

Question 23

How can a winemaker limit the potential for wines to re-ferment in bottle?

Answer 23

• Removing yeast through sterile filtration

- Add sorbic acid and SO2, which inhibits yeast from growing

Question 24

What are the downsides of adding sorbic acid to wines to prevent re-fermentation?

Answer 24

• People can smell the effects of sorbic acid at very low levels

Question 25

What microbes can live in wines with low pH and high alcohol?

Answer 25

• lactic acid bacteria

- Brettanomyces (a spoilage yeast)

Question 26

What wines are at risk for malolactic conversion starting up again in bottle?

Answer 26

Wines with lactic acid bacteria where malolactic conversion has not been carried out or completed

Question 27

Why would malolactic conversion starting up again in bottle be detrimental to the wine?

Answer 27

Would result in cloudiness in the bottle

Question 28

What are the ways to ensure malolactic conversion does not start up again in bottle?

Answer 28

1. ensure that malolactic conversion has been completed

2. filtering the wine to remove the bacteria

Question 29

How can Brett be treated?

Answer 29

• Wine can be treated with DMDC (dimethyl dicarbonate, commercial name: Velcorin) before bottling, which inactivates Brettanomyces