Chapter 16 White Winemaking Flashcards
(32 cards)
Define Skin contact
Leaving the juice in contact with the skins to extract compounds from the skins.
Define Hyperoxidation
A technique of exposing the juice to large quantities of oxygen before fermentation
Define Flotation
A clarification technique that involves bubbling gas through the juice to skim of solid particles on the top of the vessel.
Define Pectolytic enzymes
A compound that can be added to the juice that speed up the rate of sedimentation by breaking down pectins in the juice.
Define Pectins
Naturally found in plant cell walls.
Define Bâttonage
The action of steering the lees that have settle in the bottom of the vessel with the wine.
What is the main purpose of skin contact?
- To enhance the extraction of a aroma flavor compounds and precursors
- To enhance the texture of the wine by extracting small amount of tannins
Not suitable for all styles of wines, can make wine taste bitter and feel coarse in the mouth.
Why do white wine making avoid skin contact?
Because the majority of flavor and aroma compounds that are desirable for a white wine are in the pulp of the white grape.
Reasons to avoid skin contacting white wine making
- most white wines are drunk, young and tanning would not have time to soften
- Grape is all right it will extract peter flavors and astringent tannins
- not suitable for wines with delicate fruity flavors, smooth mouthfeel, and minimal color
- can add to cost as it requieres more labour, equipment and time.
When is skin contact used in white wine making?
When making white wine from an automatic weight because it maximizes flavor extraction.
Riesling, Gewuztraminer, Viognier, Muscat, Sauvignon Blanc
Time and temperature of most skin contact in white wine making
From 1 hour to 24 hours
Chilled below 15C
Why is skin contact done in lower temperatures for white white making?
- more control through reduced rate of extraction of flavors and tannins
- reduces the rate of oxidation
- reduces the threat from spoilage organisms
- reduces likelihood of spontaneous fermentation
In white wine making, what are the differences between different press fractions?
Free run juice:
- lowest in solid, tannin and color
- lower pH and higher acidity
Press juice:
- more solid, tannin and color
- Lowe acidity less sugar
- The last press fractions are likely to be too astringent or bitter (because tannins from skins, stems or seeds), and has to be discarded
What happens during hyperoxidation?
Compounds in the juice that oxidize most readily turn brown. They then precipitate during fermentation, returning the wine to its normal color.
What is the purpose of hyperoxidation?
- To produce wines that are more stable against oxidation after fermentation.
- To remove, bitter compounds that can come from unripe, bridge, skins seeds, and stems.
When is hyper oxidation not suitable in white winemaking?
It is not suitable for aromatic grape varieties that have more volatile aroma compounds that could be reduced.
If an aromatic fruity or herbaceous style of wine is desired.
Is hyperoxidation costly?
The equipment is not particularly expensive, but it is an extra step in the process that requires labor to set up and monitor, and therefore may have small impact on cost.
What is the objective of clarification of the juice?
What proportion of solace do wine makers in for?
To reduce the amount of suspended solids within the must. They include grape skins, steam and seeds.
0.5 to 2%
What does a higher percentage of solids add to the wine?
- texture
- subtle astringency (tannins from the skins and stems)
- greater range of aromas from fermentation = more complexity
- Nutrients for yeast (very low % os solids can lead to stuck fermentation)
BUT
Needs careful monitoring as the various compounds within the solids and the reactions can lead to of flavors (reductive sulfur compounds) = better suited to small volume production of premium wines
Define sedimentation.
The simplest form of clarification a.k.a. settling
The suspended solids in the juice are left to fall overtime with gravity.
Explain how is sedimentation done?
The juice is chilled to around 4°C to reduce the rate of oxidation, the threat from spoilage organisms and to avoid spontaneous fermentation.
Below 15°C sedimentation takes longer (12 to 24 hours) taking up space and time.
Sedimentation is the cheapest method in terms of equipment and is the most traditional as it requires no extra equipment or additives.
Better suited for small volume production of premium wines as it is timely and has to be done in a batch process. There is a cost to the energy used in chilling.
Explain how flotation is done
Gases is bubbled through the juice and solid particles rise to the top of the vessel. Inert gases can be used or oxygen (hyperoxidation).
Finning agents must be added to the must for this technique to be successful and cannot be used on wine.
How does flotation compare to sedimentation?
- more expensive in terms of equipment needed
- requieres fining agents, gases
- effective and quick
- can be used as a continuous or a batch process
- The juice does not need chilling, and therefore there is a saving on energy cost
Define centrifugation
A technique used to clarify wine or juice.
It uses centrifugal force to separate solids from liquids.
