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 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. Some 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?
- can add complex aromas
- helps in the stabilisation against unstable proteins that can cause hazes
- helps to protect the wine from oxygen
- provides 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 smell from high levels of hydrogen sulphide)