15.2 Stabilisation

Question 1

To what does the term ‘stabilisation’ refer?

What are the different types of stability being sought

Answer 1

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

protein stability

tartrate stability

microbiological stability

Question 2

What is the key procedure to ensuring protein stability?

Answer 2

Fining with bentonite

Question 3

Describe tartrates and how tartaric stability is achieved

Answer 3

harmless deposits of crystals that can form in the finished wine

principally potassium bitartrate

less frequently, calcium tartrate

many customers will regard these crystals as a fault thus most winemakers try to prevent them

1. Cold stabilisation

• wine held at -4°C (25°F) for ~8 days,crystals form, can then be filtered- Colloids must be removed by fining before hand as they prevent the crystals from forming at this stage

2. Contact process

• quicker, continuous, more reliable and cheaper form of cold stabilisation
• potassium bitartrate is added to the wine, wine cooled to 0°C (32°F) - after 1-2 hours crystals cb filtered out

3. Electrodialysis

• a charged membrane removes potassium and calcium ions and, to a smaller extent, tartrate ions
• after high initial investment its faster and cheaper (energy) than contact

4. Ion exchange

• does not remove tartrates - replaces potassium and calcium ions with hydrogen or sodium ions, which will not drop out of solution
• disadv sodium not allowed in all regions (despite lower than reqd levels)

5. Carboxymethylcellulose (CMC)

• prevents tartrates from developing to a visible size
• used for: inexpensive white and rosé wines
• not suitable for: red wines (causes haze)
• much cheaper than chilling
• keeps wines stable for a few years

6. Metatartaric acid

• prevents the growth of potassium bitartrate and calcium tartrate crystals
• reduces need for cold stabilisation
• quick and easy
• used on red wines
• disadv - the compound is unstable - its positive effect is lost over time, esp high temperatures (25–30°C - best for wines tb consumed early

Question 4

microbial stability issue

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

Answer 4

wines with residual sugar have potential to start fermenting if some yeast were left inthe wine.

• Removing yeast through sterile filtration
• or…Add sorbic acid and SO2, which inhibits yeast from growing disadv - People can smell the effects of sorbic acid at very low levels

Question 5

microbial stabilitiy issue 2

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

Answer 5

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

Question 6

microbial stability issue

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

Answer 6

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

Would result in cloudiness in the bottle

prevent by

1. ensure that malolactic conversion has been completed
2. filtering the wine to remove the bacteria