Oxygen and Sulfur Dioxide

Question 1

What are oxidation reactions?

Answer 1

-Ox not very reactive with many compounds in must and wine.
-the reactions it does takes part in creating products that react with must compounds

Question 2

What is oxygen a threat to?

Answer 2

-fresh, fruity wines
-aroma compounds- eg thiols, breakdown in ox= loss of fruitiness
-can cause unwanted aromas eg acetaldehyde= nutty brown apple aroma

Question 3

What does oxygen do to white wine?

Answer 3

-changes colour- darker= need greater protection
-reds have phenolic compounds= anti oxidative effect

Question 4

How can you limit oxygen?

Answer 4

-avoid ullage in vessels
-inert gases (niterogen, argon, CO2)
-impermeable vessels- ss/concrete
-cool, constant temperatures
-SO2

Question 5

Why can controlled exposure to oxygen be beneficial?

Answer 5

-O2 required in beginning of ferm= promotes healthy yeast population
- lack of ox can lead to reductive off flavours
- whites= greater oxidation stability and increased ageing potential
-reds= ox essential in reactions between anthocyanins and tannins= colour stability
- exposure to ox over time= changes in aromas over time:
dried fruits, caramel, coffee, leather etc

Question 6

How can oxygen exposure be increased?

Answer 6

-cap management
-increase number of racking and lees stirring
-small wooden barrels
-allowing ullage without inert gases
-techniques that involve pumping O2 through must (hyperoxidation/micro-oxidation)

Question 7

What are the main 2 properties that sulfur dioxide has?

Answer 7

Anti-oxidant
Anti-microbial

Question 8

What is the max limit for SO2 for reds in the EU?

Answer 8

150 mg/l

Question 9

What is the max limit for SO2 for whites in the EU?

Answer 9

200 mg/l

Question 10

If a wine contains over how many gm/l of SO2, it must state that it contains sulfites

Answer 10

10 gm/l

Question 11

When is so2 added?

Answer 11

-soon after grapes are picked/reach winery
-during WM and bottling

Question 12

Explain bound and free SO2

Answer 12

-when so2 dissolves, some of it reacts with compounds in liquid= ‘bound so2’ = ineffective against oxidation and microbes
-proportion not bound= ‘free so2’.
-small proportion of free so2= ‘molecular so2’= most effect against oxidation and microbes

Question 13

Is there are greater amount of ‘free so2’ in ‘molecular form’ at lower or higher PH levels?

Answer 13

-Lower PH levels (higher acidity)
-So wines with a higher PH (lower acidity) needs more SO2 added to protect from oxidation and microbes

Question 14

Timing and size influences the effectiveness of SO2. When is it best to add SO2?

Answer 14

-add larger amounts when grapes crushed,
-at end of malo
-and bottling
-^ more effective than adding smaller amounts throughout

Question 15

Why might wine makers want to limit amount of SO2 added?

Answer 15

-legal restrictions
-can dull aromas and cause to taste harsh