13.1. Winemaking Options: Oxygen and Sulfur Dioxide Flashcards
How does oxygen react with wine?
- oxygen itself is not very reactive with many compounds in the must and wine
- oxygen reactions create products that then go on to react with many must and wine compounds
Oxygen can be considered a threat in the production of what types of wine?
In the production of fresh, fruity wines
Name 3 reasons why oxygen can be considered a threat in the production of fresh, fruity, white wine.
- Many of the aroma compounds that give these wines their fruity style break down in the presence of oxygen, loss of fruitiness
- Example: thiols found in Sauvignon Blanc - The products of oxidation reactions may contribute to unwanted aromas to the wine
- Example: acetaldehyde (from the oxidation of ethanol) can give a nutty, apple aroma - The colour of white wines can darken, becoming gold and then brown with increased oxidation
Why do white wines require higher levels of protection from oxidation?
- The colour of white wines can darken, becoming gold and then brown with increased oxidation
- Phenolic compounds in red wines have an anti-oxidative effect, which means that they can absorb more oxygen before such effects are perceptible
What is reductive winemaking?
- AKA Protective Winemaking
- The practice of minimising oxygen exposure during the winemaking process
Name 5 ways the effects of oxygen on the must or wine can be limited.
- avoiding ullage in vessels
- use of ‘inert’ gases
- addition of sulfur dioxide
- use of impermeable containers
- cool, constant temperatures
What is ullage and why is it important when it comes to protecting wines from oxidation during winemaking?
- The headspace of air between the wine and the top of the container
- Can be avoided by ensuring vessels are filled up to the top
- In not airtight vessels (e.g. wood), gradual loss of liquid through evaporation; must be topped up regularly
How are inert gases used to protect wines from oxidation? Name 3 gases that are used.
- Used to flush out oxygen from vessels, pipes, and machinery (such as presses)
- Used to fill the empty headspace of any containers where the wine does not reach the top to prevent oxygen coming into contact with the wine
- Do not react with compounds in the wine
- Examples: Nitrogen, Carbon Dioxide, Argon
What types of fermentation vessels are impermeable to oxygen? What types of packaging?
- stainless steel
- thick concrete
- glass bottles with screwcap
Why are cool, constant temperatures important in preventing oxidation?
Cool, constant temps slow the rate of oxidation reactions
Why is some oxygen needed in winemaking?
- required at the start of fermentation of all wines to promote growth of a healthy yeast population
- in some cases, lack of enough oxygen in winemaking or storage can lead to reductive off-flavours
Why is oxygen beneficial in the production of some white wines?
Exposure to oxygen before fermentation is thought to lead to greater oxidation stability in the wine, increasing aging potential
Why is oxygen beneficial in the production of red wines?
Oxygen is essential in the reaction between anthocyanins and tannins that leads to greater colour stability
How does exposure to oxygen affect a wine over time? Give examples.
Leads to changes in the aromas/flavours of wine, which can give a greater range and diversity of characteristics
Examples:
- fresh fruits become dried fruits
- notes such as honey, caramel, coffee, leather, and mushroom can develop
Give 3 examples of types of wines where a high level of oxidation is vital.
- Oloroso Sherry
- Madeira
- Tawny Port
