13.1 Oxygen and Sulfur Dioxide - Oxygen and Must in Wine

Question 1

What is the role of oxygen in winemaking?

Answer 1

1) Responsible for reactions that take place between molecules in must / wine

Can significantly impact style / quality

Question 2

What are oxidation reactions when referring to general winemaking?

Answer 2

Oxygen reacts with must/wine compounds (not a lot).

Creates by-products that in turn react with many must/wine compounds.

Question 3

What aromas can oxygen remove from a wine?
What aromas can some oxygen add to a wine?
What aromas can a lot of oxygen add to a wine?

Answer 3

1) Generally threatening to fresh, fruity wine production (thiols in SB, performed in muscat, esters like iso-amyl acetate)

2) Deliberate oxidation aromas

3) Bottle development aromas

4) Acetaldehyde (oxidation of ethanol) can give a nutty, apple aroma

Question 4

Why is the timing and amount of oxygen important when making wine?

Answer 4

Timing makes difference between a positive or a negative impact

Understanding of role of oxygen is essential

Question 5

How can oxygen affect the colour of red wine? White wine?

Answer 5

White wines turn darker: gold to brown

Red wines are initially protected but then turn paler.

Question 6

Which requires greater protection from oxygen - red or white? Why?

Answer 6

White wines need greater protection from oxygen.

Red wines have phenolic compounds that have an anti-oxidative effect. Reds can absorb more oxygen before colour change becomes perceptible.

Question 7

What is reductive wine making?

Answer 7

The practice of minimizing oxygen exposure during the winemaking process.

Question 8

What are 4 ways to reduce oxygen exposure when making wine?

Answer 8

1) Avoiding ullage in vessels with regular top-ups

2) Inert gases in ullage or used to flush out system

3) Addition of sulfur dioxide which has strongly anti-oxidative effects

4) Use of impermeable containers (such as stainless steel or concrete)

Question 9

How does temperature slow oxidation?

Answer 9

Matt: remember the constant part.

Cool, constant temperatures slow oxidative reactions.

Question 10

What are 3 ways to maintain a cool constant temperature and prevent oxidation from occurring?

Answer 10

1) Cool cellars
2) Low fermentation temperatures
3) Night /early morning picking when

Question 11

Name 3 positive effects of oxidation

Answer 11

1) Oxygen is needed at the start of fermentation to promote growth of a healthy yeast population

Lack of enough oxygen in winemaking / storage can cause reductive off-flavours

2) White wine hyperoxidation can lead to greater oxidation stability and increased ageing potential

3) Greater colour stability in red wine

Question 12

What happens to the aroma of wine over time as it oxidizes?

Answer 12

1) Fruity flavours as terpenes, thiols and esters break down

2) Fresh fruit to dried fruit

3) Oxidative ageing

4) Bottle ageing in red wine

5) Bottle ageing in white wine

Question 13

Name 3 wine styles that need a high level of oxidation.

Answer 13

1. Oloroso Sherry
2. Madeira
3. Tawny Port

Question 14

Name 4 aromas of deliberately oxidated white wine.

Answer 14

1. Walnuts
2. Hazelnuts
3. Almonds
4. Marzipan

Question 15

Name 4 aromas of deliberately oxidated red wine.

Answer 15

1. Toffee
2. Coffee
3. Chocolate
4. Caramel

Question 16

Name 6 ways to increase oxygen exposure when making wine.

Answer 16

1)** Cap management** techniques in RW fermentation
* Spray or splash to oxygenate

2) Rackings and lees stirrings – increase

3) Small wooden barrels that contain small volume of red wine relative to amount of wood

4) Ullage space, using no inert gases

5) Any procedure where bung/lid is removed and wine inside moved

6) Micro-oxygenation

Question 17

Name 2 spoilage mechanisms.

Answer 17

1. Acetic acid bacteria
2. Brettanomyces

Question 18

What encourages the growth of spoilage mechanisms?

Answer 18

Oxygen favours growth of spoilage organisms, espeically when there is residual sugar.

Question 19

How do winemakers ensure that spoilage mechanisms do not start to grow? Does this incur extra cost?

Answer 19

Careful monitoring. This requires extra labour, which can increase costs.