Chapter 16 White Winemaking

Question 1

Define Skin contact

Answer 1

Leaving the juice in contact with the skins to extract compounds from the skins.

Question 2

Define Hyperoxidation

Answer 2

A technique of exposing the juice to large quantities of oxygen before fermentation

Question 3

Define Flotation

Answer 3

A clarification technique that involves bubbling gas through the juice to skim of solid particles on the top of the vessel.

Question 4

Define Pectolytic enzymes

Answer 4

A compound that can be added to the juice that speed up the rate of sedimentation by breaking down pectins in the juice.

Question 5

Define Pectins

Answer 5

Naturally found in plant cell walls.

Question 6

Define Bâttonage

Answer 6

The action of steering the lees that have settle in the bottom of the vessel with the wine.

Question 7

What is the main purpose of skin contact?

Answer 7

• 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.

Question 8

Why do white wine making avoid skin contact?

Answer 8

Because the majority of flavor and aroma compounds that are desirable for a white wine are in the pulp of the white grape.

Question 9

Reasons to avoid skin contacting white wine making

Answer 9

• 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.

Question 10

When is skin contact used in white wine making?

Answer 10

When making white wine from an automatic weight because it maximizes flavor extraction.

Riesling, Gewuztraminer, Viognier, Muscat, Sauvignon Blanc

Question 11

Time and temperature of most skin contact in white wine making

Answer 11

From 1 hour to 24 hours
Chilled below 15C

Question 12

Why is skin contact done in lower temperatures for white white making?

Answer 12

• 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

Question 13

In white wine making, what are the differences between different press fractions?

Answer 13

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

Question 14

What happens during hyperoxidation?

Answer 14

Compounds in the juice that oxidize most readily turn brown. They then precipitate during fermentation, returning the wine to its normal color.

Question 15

What is the purpose of hyperoxidation?

Answer 15

• 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.

Question 16

When is hyper oxidation not suitable in white winemaking?

Answer 16

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.

Question 17

Is hyperoxidation costly?

Answer 17

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.

Question 18

What is the objective of clarification of the juice?

What proportion of solace do wine makers in for?

Answer 18

To reduce the amount of suspended solids within the must. They include grape skins, steam and seeds.

0.5 to 2%

Question 19

What does a higher percentage of solids add to the wine?

Answer 19

• 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

Question 20

Define sedimentation.

Answer 20

The simplest form of clarification a.k.a. settling

The suspended solids in the juice are left to fall overtime with gravity.

Question 21

Explain how is sedimentation done?

Answer 21

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.

Question 22

Explain how flotation is done

Answer 22

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.

Question 23

How does flotation compare to sedimentation?

Answer 23

• 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

Question 24

Define centrifugation

Answer 24

A technique used to clarify wine or juice.

It uses centrifugal force to separate solids from liquids.

Question 25

Explain advantages and disadvantages of centrifugation

Answer 25

• quick
• used continuously
• can be used on juice or wine
• expensive to buy (better suited for larger volumes)
• Increase the juice exposure to oxygen, unless it is flushed with inert gases (more costly)

Question 26

Explain how pectolytic enzymes work

Answer 26

They breakdown pectins in the juice which allows for more rapid separation between the liquid juice and solids. They can only be used on juice.

The time and energy saved compared to the sedimentation can justify the cost of purchasing these agents.

Question 27

What is the fermentation temperature for white wines and why?

Answer 27

Around 15°C

Because the volatile aromas and flavors compounds that are desired in many white wines are best produced and retained at cool temperatures.

Question 28

Why in some styles of white wines fruity aromas are not particularly desired?

What can be done to avoid them?

Answer 28

In white wine making were oak is going to be used to provide flavors the winemaker might want to avoid fruity aromas.

The fermentation can be slightly warmer from 17 to 25°C (and sometimes higher) to avoid the production of certain esters such as isoamyl acetate (banana like smell)

Question 29

In white wine making what are the effects of malolactic conversion?

Answer 29

• Reduction of acidity
• increase in microbiological stability
• modification to the flavors of wine

Question 30

In white wine making what are the objectives of lees aging?

Answer 30

• give more body
• The mouth feel
• help to stabilize the wine
• Protect the wine from oxygen
• May introduce some reductive sulfur compounds, which can be desirable at low levels

Question 31

Explain the effects of battonage

Answer 31

• Increase the release of yeast compounds into the wine
• reduction of the development of reductive, sulfur compounds and the aromas they can produce
• Small exposure of oxygen and decrease in fruity flavors

Question 32

How is skin contact done in white wine making?

Answer 32

• The time can range from an hour to 24 hours (or more)
• is coming to cool the juice to below 15°C to reduce the rate of extraction of flavors and tannins permitting more control, and reducing the rate of oxidation and the threat from spoilage organisms AND fermentation
• If skin contact is carried out after the fermentation begins, the resulting wine are called orange wines