General winemaking options: Oxydation management & S02

Question 1

Why does oxygen have a significant role to play in wine making?

Answer 1

Oxygen is responsible for a number of reactions that take place between molecules in the grape must and wine: Oxidation reactions

Question 2

What two things dictate whether or not exposure to oxygen has a positive or negative effect on the winemaking process?

Answer 2

Timing and amount of oxygen

Question 3

What effect does oxygen exposure typically have on fresh, fruity wine making? Why?

Answer 3

Oxygen is generally bad for this style of wine. Many of the compounds that give these wines their fruity style break down in presence of oxygen.

Question 4

What is an example of an unwanted flavour compound that is creates by exposure to oxygen? What does it smell and taste of?

Answer 4

Acetaldehyde (oxydation of Ethanol)

Flavours of apple and nuts.

Question 5

What happens to the colour of white wines when exposed to oxygen?

Answer 5

They turn darker, first golden then eventually brown.

Question 6

What in red wines protects the wine from the effects of oxygen?

Answer 6

Polyphenols including tannins mean that oxygen has less of an initial effect in in red wine.

Question 7

What is reductive winemaking?

Answer 7

The practice of minimising oxygen exposure during the winemaking process.

Question 8

Five ways oxygen exposure can be reduced during winemaking.

Answer 8

• Avoiding ullage
• Blanketing with inert gases
• Addition of sulphur dioxide
• Use of impermeable containers (e.g. Stainless steel)
• Cool constant temperatures

Question 9

What is ullage? Why is it important to control?

Answer 9

Ullage is the headspace at the top of a vessel containing wine. This includes stainless steel tanks and oak barrels The empty space at the top of a vessel will contain oxygen. Prolonged exposure to the oxygen will cause oxidation.

Question 10

How can inert gases be used to control oxidation?

Answer 10

By flushing presses, pipes and tanks with inert gas this removes oxygen and reduces the contact between wine and oxygen.

Question 11

How can cool temperatures help control oxidation? Name two ways this can be achieved?

Answer 11

Cool temperatures slow down the oxidation reaction.

1. Picking grapes early in the morning so that they are cool
2. Maturing wine in a cool environment

Question 12

How can oxygen contact be a positive in winemaking?

Answer 12

Oxygen is required to aid fermentation

Lack of oxygen can lead to off flavours (reductive)

Exposing the must to oxygen before fermentation can lead to greater oxygen stability in the wine and result in increased ageing potential.

Some wines are oxidised in style e.g. Olorosso Sherry and Madeira

Question 13

What specific advantage is there to oxygen exposure in red wines?

Answer 13

Oxygen can aid colour stabilisation in red wines.

Question 14

How can oxygen exposure be increased when making red wines?

Answer 14

• Cap management
• Use of small wooden barrels
• Increasing the number of rackings
• Allowing ullage without the use of inert gas
• Micro-oxygenation

Question 15

What unwanted side effect can exposure to oxygen lead to?

Answer 15

Oxygen can favour the growth of spoilage organism such as acetic acid bacteria and brettanomyces

Question 16

How much S02 is naturally produced during fermentation?

Answer 16

10mg/L

Question 17

what is S02?

Answer 17

Sulfur dioxide is a preservative with Anti-oxidant and Anti-microbial properties.

SO2 can be applied in various forms: gas, liquid or solid, as sulfur dioxide, potassium metabisulfite or potassium bisulfite.

Question 18

What is the maximum concentration levels of S02 in the EU?

Answer 18

Red wines = 150 mg/L
White wines = 200 mg/L
Sweet wines are permitted to contain higher levels.

Lower levels for Organic wines

Over 10 mg/L of SO2, the label must state that the wine contains sulfites.

In USA Organic wines = No addition of S02

Question 19

Define Bound S02, Free S02 and Molecular S02

Answer 19

When SO2 is added to must or wine, it dissolves and some of it reacts with compounds in the liquid. This proportion is called ‘bound SO2’ and it is ineffective against oxidation and microbes.

The proportion that is not bound is called ‘free SO2’. The vast majority of the free SO exists in
a relatively inactive form and a small proportion exists as molecular SO2, which is the most effective against oxidation and microbes

Question 20

How does PH level affect S02?

Answer 20

The pH level of the must or wine has a key effect on the efficacy of SO2 in that a greater proportion of free SO2 is in the molecular form at lower pH levels.

This means that a greater amount of SO2 needs to be added to musts and wines with relatively high pH to protect them from oxidation and microbes.

Question 21

When is the most effective time of adding S02?

Answer 21

• Crushing
• End of MALO
• Bottling

Question 22

What practices can limit the amout of S02 needed to guarantee unfaulty wine?

Answer 22

• Good winery hygiene
• Effective grape sorting can limit the amount of harmful microbes in the wine and the winery
• Limiting oxygen exposure
• keeping grapes, must or wine at cool temperatures can also reduce the amount of SO2 needed to protect from oxidation and spoilage organisms.