14.3 The Role of Lees in Still Wine Maturation Flashcards
What are lees?
the sediment that settles at the bottom of a wine vessel
What makes up lees?
- dead yeast
- dying yeast and bacteria
- grape fragments
- precipitated tannins
- nutrients
- other insoluble compounds
What are the gross lees?
The sediment that forms quickly after the end of fermentation (within the first 24 hours)
How are gross lees different from lees?
made up of the larger, heavier particles
What are fine lees?
the sediment formed from smaller particles that settle more slowly
What is racking?
The process of removing the lees from the wine
What lees are removed during the first racking? Subsequent rackings?
- first: gross lees,
- subsequent periodic racking helps to manage the levels of fine lees
What is autolysis?
- When the yeast cells very slowly die and break down after fermentation
- Release compounds that contribute flavours, body and texture to the wine
Describe, scientifically, what happens during autolysis.
- Yeast cells die and break down
- Release compounds:
1. Some compounds bind with phenolic compounds in the grapes, reducing colour and softening tannins
2. Compounds bind with certain extractable components of the wood, such as wood tannins and flavours, and can therefore reduce astringency and modify the flavours from the wood
In what wines are the effects of the lees generally more significant?
White wines
Name some autolytic flavors.
yoghurt-like, dough-like, biscuity or toasty
What are the benefits of lees?
- stabilisation of the wine against unstable proteins that can cause hazes
- slow, controlled oxidation reduces need for so2
- provide nutrients for microbes (can assist the growth of lactic acid bacteria for malolactic conversion)
How do lees help in protecting the wine from oxygen?
- help to maintain a slow, controlled oxidation during maturation
- lower the need to use SO2 during this time
What could happen if the layer of lees is too thick? For what types of lees is this particularly a problem?
- can produce volatile, reductive sulfur compounds
- can be good (add complexity, aromas of struck match and smoke)
- can be bad (smell of rotten eggs) - can encourage the development of spoilage microbes such as Brettanomyces
- gross lees
What is reduction?
A wine fault
- can contribute unpleasant aromas (e.g. rotten egg small from high levels of hydrogen sulphide)
What is bâtonnage?
The stirring of the lees
How can lees increase the cost of the final wine?
- Lees ageing may increase the time the wine is stored at the winery before release
- Wines aged on lees (particularly gross lees) need to be monitored regularly and may be stirred, which incurs a labour cost.
What is racking? How is it typically done?
- The process of transferring wine from one vessel to another with the aim of removing sediment from the wine
- The wine is removed from the original vessel through a valve near the bottom of the vessel (above the top of the sediment) and pumped or poured into the top of a new, clean vessel.
Other than lees removal, what effect does racking have on the wine?
- Oxidation
How can wines be protected from oxidation during racking? For which types of wines might this be done?
- using pressure from inert gas to push the wine out through a hose into the new vessel, which would have been flushed with an inert gas
- aromatic or fruity wines
How many times is racking carried out and what does this depend on?
- once or several times during the maturation process
Depends on:
– how long the wine is stored
– whether it is stored with or without lees
– whether the winemaker wants to increase oxygen exposure
