Oxygen in Winemaking Flashcards
Why does oxygen have a significant role to play in winemaking?
Oxygen is responsible for a number of reactions that take place between molecules in the grape must and wine.
What are reactions that oxygen is responsible for?
Oxidation reactions
What two things dictate whether or not exposure to oxygen has a positive or negative effect on the winemaking process?
- timing
- amount of oxygen
What effect does oxygen exposure typically have on fresh, fruity winemaking? Why?
Oxygen is generally bad for this style of wine. Many of the compounds that give these wines their fruity style break down in the presence of oxygen.
What is an example of an unwanted flavor compound that is created by exposure to oxygen? What does it smell and taste of?
- acetaldehyde
- flavors of apple and nuts
What happens to the color of white wines when exposed to oxygen?
They turn darker, first golden, then eventually brown.
What in red wines protects the wine from the effects of oxygen?
Polyphenols, including tannins, mean that oxygen has less of an initial effect in red wine.
What is reductive winemaking?
The practice of minimizing oxygen exposure during the winemaking process.
Five ways oxygen exposure can be reduced during winemaking?
- avoid ullage
- blanketing with inert gas
- addition of SO2
- use of impermeable containers
- cool, constant temperatures
What is ullage? Why is it important to control?
Ullage is the headspace at the top of a vessel containing wine (includes SS tanks and barrels).
The empty space at the top of a vessel will contain oxygen, and prolonged exposure to the oxygen will cause oxidation.
How can inert gases be used to control oxidation?
By flushing presses, pipes, and tanks with inert gas, this removes oxygen and reduces the contact between wine and oxygen.
How can cool temperatures help control oxidation? Name two ways this can be achieved.
Cool temps slow down the oxidation reaction.
- pick grapes early in the morning so they are cool
- maturing wine in a cool environment
How can oxygen contact be a positive in winemaking?
- oxygen is required to aid fermentation
- lack of oxygen can lead to off flavors (reductive)
- exposing the must to oxygen before fermentation can lead to greater oxygen stability in the wine, and result in increased aging potential
- some wines are oxidized in style, e.g. Oloroso and Madeira
What specific advantage is there to oxygen exposure in red wines?
Oxygen can aid color stabilization in red wines
How can oxygen exposure be increased when making red wines?
- cap management
- use of small wooden barrels
- increasing the number of rackings
- allowing ullage without the use of inert gas
- micro-oxygenation
