D1 Finishing - Clarification, Stabilisation, Adjustments

Question 1

Finishing

Answer 1

The aim after maturation, lees ageing and blending is to make a wine clear and stable before packaging.

Question 2

Post-fermentation Clarification - Sedimentation, Centrifugation

Answer 2

Sedimentation
In cool cellar conditions, clarification naturally occurs over time. The particles precipitate at the bottom and the sediment is removed by racking.
It is the gentlest system, therefore avoid potential loss of flavour and texture.
Add cost on time and labour.
If the wine is barrel-aged, sedimentation will be part of this process.

Centrifugation
Spins the wine at high speed to clarify it.
This process is invasive, potential loss of delicate flavours.
Allow early bottling, therefore suitable for high volume.
Machine are expensive, high volume cover the cost.

Question 3

Post-fermentation Clarification - Fining

Answer 3

Fining speeds up the process of precipitations.
Remove unstable colloids (microscopic particles too small to be removed by filtering) that may form hazes.

There are three categories:
1. Fining agents that removes unstable grape proteins (prevent hazes)
- Bentonite. a form of clay that absorb unstable grape protein. It produces lots of sediment, so wine is lost during racking.

2. Fining agents that remove phenolics that contribute undesirable colour and bitterness.
   (remove browning and astringency, give brightness)
   - Egg white. Gentle
   - Gelatine. from pork collagen (over-fining may disrupt flavours and increase risk of protein haze later)
   - Casein.
   - Isinglass. from fish bladders (over-fining increase risk of protein haze and fishy smell)
   - Vegetable protein (potato or legume)
   - PVPP. insoluble plastic in powder. gentler than charcoal.
3. Fining agent that removes colour and off-odours
   - Charcoal. (over-fining remove desirable aromas and flavour)

Question 4

Post-fermentation Clarification - Filtering

Answer 4

Filtering eliminates solids.
The two main type are:

1. Depth filtration
   - Diatomaceous earth (DE) is silica and inert.
   Used on Rotary vacuum filters.
   Cost of the machine is high though the per litre cost after is small.
   - Sheet filter
   Cost of machine is high, although the cost of the sheets is low.
2. Surface filtration also called sterile filtration because remove ant yeast and bacteria.
   - Membrane filters.
   Slower, as pores are smaller (less than 1 micron).
   Wine is usually pre-filtered, otherwise can get blocked.
   Usually used before bottling because makes the wine clear and microbiologically stable.
   Cost of machine is small, but the cartridges are expensive.
   - Cross-flow filters.
   It is quicker, and it cleans the surface as is works, eliminating the cost of the cartridges.
   However, the machines are expensive.

Question 5

Post-fermentation Stabilisation

Answer 5

A not stable wine could lead to hazes, deposit and rapid browning.

1. Protein stability
   - Fining with Bentonite.
2. Tartrate stability. Potassium bitartrate and Calcium tartrate can form deposit of crystals.
   - Cold stabilisation.
   Wine is kept at -4C for 8 days so that the crystals form and then is filtered.
   Requires cost of equipment and energy.
   Only removes Potassium bitartrate.
   - Contact process.
   Is quicker, continuous and cheaper.
   Wine is kept at 0C for few hours, Potassium bitartrate is added to speed up the crystallisation process, then is filtered.
   - Electrodialysis.
   Uses a charged membrane to remove selected ions (in this case can remove both potassium and calcium ion).
   Cost of machine is high, but lower that cold stabilisation later as uses less energy and it is faster.
   - CMC (white wines only)
   Wood cellulose prevent tartrates from developing.
   Is cheaper than chilling but keeps the wine stable only for few years.
   - Metatartaric acid (red wines mostly)
   Adding this compound prevent the growth of both tartrates, however is more unstable at high temperature.
   Is cheaper than chilling but keeps the wine stable for less than CMC.
3. Microbiological stability (from yeast, bacteria and spoilage organisms)
   - RS may cause re-fermentation in the bottle. To avoid this, removal of yeast through filtration or add sorbic acid and SO2 (which inhibits yeast from growing)
   - Lactic acid bacteria may start conversion again in the bottle (causing haze), remove the bacteria or filter the wine.
   - If Brettanomyces is present, remove by filtering of with DMDC (Dimethyl bicarbonate “Velcorin”), which inactivates Brettanomyces.

Question 6

Finishing and adjustments

Answer 6

Before finishing, a full chemical lists measures alcohol, RS, free SO2, dissolved oxygen and CO2.

Adjustments
- Adjust level of Sulfur dioxide SO2, must be within legal limits.
Excessive amount lead to off smell (rotten egg, cabbage) and bleaching colour.
- Reduce dissolved oxygen.
As it can accelerate the speed of ageing, reducing its shelf life. It can be removed by flushing with inert gas.
- Adding Carbon Dioxide CO2.
Add freshness, especially for inexpensive white and rose.

Question 7

Faults

Answer 7

• Cloudiness and hazes
  Cause:
  Due to the growth of yeast and bacteria.
  Poor hygiene, poor filtering, over-fining.
  Solution:
  Full chemical analysis to act if necessary.
  Better hygiene, better filtering.
• Tartrates (crystals)
  Cause:
  Triggered by low temperature and poor filtering.
  Solution:
  Full chemical analysis to act if necessary.
  Tartrates stabilisation.
• Re-fermentation in bottle (bubbles, cloudiness)
  Cause:
  unwanted re-fermentation in the bottle, due to poor filtering.
  Solution:
  Better filtering
• Cork taint (mouldy, cardboard smell, reduce fruit character and shorter the finish of wines)
  Solution:
  Use of technical cork
• Oxidation (browning, loss of primary fruit, vinegary smell)
  Cause:
  Excessive exposure to oxygen due to packaging, poor corks
• Volatile acidity (nail varnish/vinegar smell)
  Cause:
  Acetic acid bacteria, inadequate level of SO2, excess exposure to oxygen.
  Solution:
  Full chemical analysis to act if necessary.
  Sorting fruit to exclude damage grapes, better hygiene, avoid ullage, careful racking.
• Reduction (sulfur like smell struck match, smoke to onion, rotten egg, cabbage)
  Cause:
  Higher level of volatile, reductive sulfur compounds compare to oxygen.
  Produce by yeast under stress (due to low nitrogen level), or due to too little oxygen during maturation, lees ageing and after packaging.
  Solution:
  Make sure yeast is not stressed, ensuring sufficient nutrients and oxygen.
  Adjust SO2 level to balance with the oxygen level.
• Light strike (dirty drain smell)
  Cause:
  Volatile sulfur compounds caused UV radiation in clear glass bottles.
  Solution:
  Choice of packaging.
• Brettanomycides (animal, spicy, farmyard smell. reduce fruit flavours, acidity and tannins)
  Brett lives in the wood of barrels.
  Solution:
  Better hygiene.
  Maintaining effective SO2 levels.
  Keeping pH levels low so that SO2 can be added asap.
  Can be filtered by filtration or with fining agent DMCD (dimethyl bicarbonate “Velcorin”), which inactivates brettanomyces.