4.1 The Role of Oxygen in Maturation

Question 1

Generally, what effect does oxidation have on wine flavors?

Answer 1

• gradual reduction in many primary aromas

- development of tertiary aromas (dried fruit, nuts)

Question 2

Describe the conditions required for oxidation to enhance a wine’s quality.

Answer 2

• primary aromas develop into pleasant tertiary aromas

- wine has a structure suitable for extended ageing

Question 3

Describe the negative effects of oxidation on wine.

Answer 3

• primary flavours fade

- not replaced by positive tertiary characteristics

Question 4

How does oxidation affects the colour of white wines?

Answer 4

• white wines become darker, gradually becoming gold and then brown

Question 5

What happens when light-coloured red wines are exposed to oxygen?

Answer 5

• can result in greater colour stability and intensity

- anthocyanins bind with tannins (protects anthocyanins from being adsorbed by yeast lees or bleached by SO2 additions)

Question 6

How does oxidation affects the colour of red wines?

Answer 6

After much more extensive ageing, red wines gradually become paler and browner.

Question 7

How does oxidation affects red wines in general?

Answer 7

• Softens tannins

- may be linked to anthocyanin and tannin bonding

Question 8

Why can red wines withstand a higher level of oxygen exposure than white wines before any signs of oxidation are apparent?

Answer 8

due to their higher content of anti-oxidative phenolic compounds (e.g. tannins)

Question 9

On average, how long do red wines spend maturing pre-bottling?

Answer 9

12–24 months

Question 10

On average, how long do white wines spend maturing pre-bottling?

Answer 10

6–12 months

Question 11

What affect does temperature have on oxidation rates?

Answer 11

warm temperatures increase the speed of oxidation reactions

Question 12

Name a wine in which a high level of oxidation is a key part of its style. Describe the wine.

Answer 12

Oloroso Sherry

• brown colour
• lack of fresh fruit
• nuts and dried fruits

Question 13

How are wines that require a high level of oxidation matured?

Answer 13

• the wine is stored for a number of years in barrels that are not filled to the top
• allows oxygen within the headspace of the barrel (ullage)

Question 14

What is ullage?

Answer 14

allowing oxygen within the headspace of the barrel

Question 15

What is the most commonly used method of gaining a slow, gradual exposure to oxygen?

Answer 15

• store the wine in small wooden vessels

Question 16

Describe how wooden vessels slowly oxidize wine.

Answer 16

• Some oxygen is released from the pores in the vessel within the first month that the vessel is filled with wine.
• A very small amount of oxygen continues to pass through the gaps between the staves and the bung hole.

Question 17

What are the two main schools of thought related to how wine in barrel is exposed to oxygen?

Answer 17

1. oxygen only enters through the bung hole

2. while others suggest oxygen passes through the wood itself

Question 18

At what point in winemaking is a wine most exposed to oxygen?

Answer 18

During any transfer of the wine in which the bung is removed. Examples:

• racking
• lees stirring
• topping up

Question 19

Describe how some wine is generally lost during the maturation process in wooden vessels.

Answer 19

• Water and alcohol in liquid form impregnate the wood
• Within the staves of wood the water and alcohol turn to vapour (evaporate) and diffuse, along the concentration gradient, to the air outside the vessel
• leads to a gradual concentration of the other components of the wine

Question 20

What effect does the size of the wooden vessel have on evaporation? What is required and how does that effect the end wine?

Answer 20

• Small vessels: large surface area to volume ratio, increasing the rate at which wine is lost
• Need to be topped up with more wine to keep them full (to avoid ullage)
• topping up frequency leads to more oxygen exposure in these vessels than in much larger vessels.

Question 21

What effect does the size of the wooden vessel have on oxidation?

Answer 21

Smaller vessels:

• larger the amount of oxygen enters the barrel relative to the volume of wine
• leads to quicker (but not extreme) oxidation

Question 22

What is micro-oxygenation? What’s the typical unit used for measuring micro-oxygenation?

Answer 22

• a cheaper alternative to barrel aging
• involves bubbling oxygen through wine
• dose of oxygen typically in units of mg/L per month

Question 23

In what type of vessel is micro-oxygenation typically carried out? For how long?

Answer 23

• stainless steel tanks

- for a number of months post alcoholic fermentation

Question 24

Initially, on what types of wines was micro-oxygenation typically carried out? Now, what types of wines is it used for?

Answer 24

• Initially used for inexpensive and mid-priced wines

- Now, used for premium and super-premium wines

Question 25

What are the benefits of micro-oxygenation?

Answer 25

• increase colour stability and intensity
• soften tannins
• improve texture
• reduce unripe, herbaceous flavours
• provides the effects of gentle exposure to oxygen more quickly than barrel ageing without needing expensive barrels
• the rate of oxygen exposure can be controlled much more tightly than it could be in a barrel

Question 26

Why must care be taken when carrying out micro-oxygenation?

Answer 26

• more favourable environment for spoilage microbes (acetic acid bacteria and Brettanomyces)

Question 27

What 3 things do we not know for sure when it comes to micro-oxygenation?

Answer 27

• relatively new technique; not much research on
  1. which grape varieties or types of wines benefit from micro-oxygenation
  2. how wines made by micro-oxygenation age in bottle over the long term
  3. difference compared to the same wine matured in barrel

Question 28

At what temperature are white wines typically stored?

Answer 28

8–12°C (46–54°F)

Question 29

At what temperature are red wines typically stored?

Answer 29

12–16°C (54–61°F)

Question 30

Why are red wines typically stored at slightly warmer temperatures than white wines?

Answer 30

they are less susceptible to the effects of oxidation

Question 31

Why do stable, cool temperatures give a slower maturation than warm temperatures?

Answer 31

due the effect of temperature on chemical reactions that happen between various compounds within the wine

Question 32

Does the temperature itself directly speed up the aging?

Answer 32

No, temperature determines what reactions can occur and how quickly various reactions will occur.

Question 33

How does humidity affect aging?

Answer 33

• low humidity and warm temperatures increase the rate of wine loss
• reduces the volume of wine to sell
• barrels need topping up more often (greater cost through labour requirement)
• risk of oxidation is increased (harmful for quality)

Question 34

What is the effect of extremely low humidity (under approximately 70 per cent) on wine?

Answer 34

• Cause water to be lost at a greater rate than alcohol and, over time, this can lead to a higher alcohol concentration in the wine

Question 35

Why were many traditional cellars built underground?

Answer 35

To keep a cool, constant humidity and temperature

Question 36

In modern cellars, how are temperature and humidity controlled?

Answer 36

Temperature- and humidity-control systems