14.3 The Role of Lees in Still Wine Maturation

Question 1

What are lees?

Answer 1

the sediment that settles at the bottom of a wine vessel

Question 2

What makes up lees?

Answer 2

• dead yeast
• dying yeast and bacteria
• grape fragments
• precipitated tannins
• nutrients
• other insoluble compounds

Question 3

What are the gross lees?

Answer 3

The sediment that forms quickly after the end of fermentation (within the first 24 hours)

Question 4

How are gross lees different from lees?

Answer 4

made up of the larger, heavier particles

Question 5

What are fine lees?

Answer 5

the sediment formed from smaller particles that settle more slowly

Question 6

What is racking?

Answer 6

The process of removing the lees from the wine

Question 7

What lees are removed during the first racking? Subsequent rackings?

Answer 7

• first: gross lees,

- subsequent periodic racking helps to manage the levels of fine lees

Question 8

What is autolysis?

Answer 8

• When the yeast cells very slowly die and break down after fermentation
• Release compounds that contribute flavours, body and texture to the wine

Question 9

Describe, scientifically, what happens during autolysis.

Answer 9

• 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

Question 10

In what wines are the effects of the lees generally more significant?

Answer 10

White wines

Question 11

Name some autolytic flavors.

Answer 11

yoghurt-like, dough-like, biscuity or toasty

Question 12

What are the benefits of lees?

Answer 12

• 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)

Question 13

How do lees help in protecting the wine from oxygen?

Answer 13

• help to maintain a slow, controlled oxidation during maturation
• lower the need to use SO2 during this time

Question 14

What could happen if the layer of lees is too thick? For what types of lees is this particularly a problem?

Answer 14

1. can produce volatile, reductive sulfur compounds
   - can be good (add complexity, aromas of struck match and smoke)
   - can be bad (smell of rotten eggs)
2. can encourage the development of spoilage microbes such as Brettanomyces
   - gross lees

Question 15

What is reduction?

Answer 15

A wine fault

- can contribute unpleasant aromas (e.g. rotten egg small from high levels of hydrogen sulphide)

Question 16

What is bâtonnage?

Answer 16

The stirring of the lees

Question 17

How can lees increase the cost of the final wine?

Answer 17

• 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.

Question 18

What is racking? How is it typically done?

Answer 18

• 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.

Question 19

Other than lees removal, what effect does racking have on the wine?

Answer 19

• Oxidation

Question 20

How can wines be protected from oxidation during racking? For which types of wines might this be done?

Answer 20

• 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

Question 21

How many times is racking carried out and what does this depend on?

Answer 21

• 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