13.1 Oxygen and Sulfur Dioxide - Sulfur Dioxide

Question 1

Name the 2 main functions of SO2.

Answer 1

1. Anti-oxidant
2. Anti-microbial

Question 2

How does SO2 act as an antioxidant?

Answer 2

• SO2 only reacts with oxygen itself very slowly
• Reacts with the PRODUCTS (e.g., oxidative enzymes) of oxidative reactions
• These products cannot oxidize further compounds in the wines

Question 3

How does SO2 act as an anti-microbial?

Answer 3

• Inhibits development of microbes (yeast and bacteria)
• Different species vary in SO2 tolerance

Question 4

In what state is SO2 applied?

Answer 4

Gas, solid or liquid.

Question 5

Name 3 chemical forms of SO2.

Answer 5

1. Sulfur dioxide
2. Metabisulfite
3. Potassium bisulfite

Question 6

Does SO2 occur naturally? In the context of wine, how does it occur? What amount are produced?

Answer 6

Small amounts (10 mg/L) naturally produced during fermentation

Question 7

What are the maximum allowable levels of SO2?

Answer 7

• 160 mg/L for red, 210 mg/K white
• Sweet wines permitted higher levels
• Organic wines – lower levels

Question 8

Is SO2 a toxic substance?

Answer 8

Yes. Its use is determined by local law.

Question 9

What can So2 cause in some people?

Answer 9

Allergic reactions

Question 10

If a bottle of wine contains more than 10 mg/L of SO2, what must happen?

Answer 10

“Contains Sulfites” must be printed on the label.

Question 11

Do natural wine producers use SO2?

Answer 11

Usually no, but may in tiny amounts.

Question 12

Is SO2 found in organic wines in the US?

Answer 12

No. SO2 use in organic wines is forbidden in the US.

Question 13

At what points in the winemaking process is SO2 often used?

Answer 13

Larger amounts added at
1. Crushing
2. End of MLF
3. Bottling

Question 14

Is it better to add SO2 throughout the winemaking process?

Answer 14

No. Adding it in small amounts at each step of the winemaking process is less effective than adding it in larger amounts at 3 stages: crushing, end of MLC and bottling.

Question 15

What is “bound” SO2?

Answer 15

“Bound” SO2 reacts with compounds in the liquid

Question 16

What is “free” SO2?

Answer 16

“Free” SO2 is not bound with compounds in the liquid.

Question 17

“Free” SO2 consists of what?

Answer 17

1. Free SO2 - relatively inactive form
2. Molecular SO2 - most effective against oxidation / microbes

Question 18

What is the largest component of free SO2?

Answer 18

Most of free SO2 is inactive. A small percentage of free SO2 consists of molecular SO2.

Question 19

Describe the 3 subcomponents of SO2.

Answer 19

1. Bound SO2
2. Free SO2
3. Molecular SO2

Question 20

How does pH affect SO2 efficiency?

Answer 20

Lower pH = a greater proportion of free SO2 is in the molecular form.

Question 21

How do musts and wines with higher pH affect SO2 application?

Answer 21

Higher pH lowers the amount of molecular SO2. Therefore, wines need a greater amount of SO2 to be added in order to effectively protect them from microbes and oxidation.

Question 22

What happens to a wine if too much SO2 is added?

Answer 22

High levels:
1. Dull aromas / flavours
2. Makes wine harsh

Question 23

Name 4 ways to minimize use of SO2.

Answer 23

1. Good winery hygiene
2. Effective sorting
3. Limiting oxygen exposure
4. Cool temperatures