16. Specific Options for White Winemaking

Question 1

What is the purpose of skin contact for white wines?

Answer 1

To enhance the extraction of aroma and flavour compounds and precursors, and to enhance the texture of the wine by extracting a small amount of tannin.

Question 2

Why are most white wines not subjected to skin contact?

Answer 2

The principal aroma and flavour compounds of white grapes that are desirable in white wines are in the pulp.

Question 3

What are the reasons a winemaker would subject their white wines to minimal or no skin contact?

Answer 3

• Where delicate fruit flavours, minimal colour and smooth mouthfeel are desired.
• For early consumption wines, because the tannins that would be extracted would not have time to soften.
• If fruit is underripe, so not to extract bitter tannins and flavours.
• A period of skin contact slows down winemaking process, and requires equipment and labour
• Some winemakers believe skin contact leads to homogenisation; reducing the variations grape varieties and different vineyard sites.

Question 4

What grape varieties is skin contact most effectively used? Why

Answer 4

Aromatic grape varieties such as Riesling, Gewurtztraminer, Muscat and Sauvignon Blanc.
These have lots of aroma compounds that can be extracted from the skins.

Question 5

What are the two key factors that influence extraction during skin contact in white wines?

Answer 5

Time
Temperature

Question 6

How long does skin contact last for in white wine production?

Answer 6

Skin contact times can range from around an hour to 24 hours and over, with greater time on skins leading to greater extraction of flavour and tannins.

Question 7

At what temperature are white wines kept during skin contact? Why?

Answer 7

Juice is typically chilled to below 15°C.

This reduces the rate of extraction of tannins and flavours, permitting more control, and also reduces the rate of oxidation and the threat from spoilage organisms, including likelihood of a spontaneous fermentation.

Question 8

When does skin contact for white wines usually occur?

Answer 8

After crushing
Before pressing and fermentation

Question 9

What are orange/amber wines?

Answer 9

White wines that have been fermented on their skins.

Question 10

How do orange wines differ in structure and flavour than white wines?

Answer 10

Their taste profile can be markedly different to typical white wines, as different aromatic and phenolic compounds are extracted from the skins. Orange wines can have notable levels of tannin and characteristics such as dried fruit, dried herbs, hay or nuts.

Question 11

Why might a winemaker choose to press whole bunches of white grapes?

Answer 11

• Reduces the chance of oxidation before and during pressing, especially if inert gases, such as nitrogen, carbon dioxide or dry ice (carbon dioxide in solid form), are used within the press.
• It is one of the gentlest forms of pressing, providing juice that is low in solids (grape skin, stem and seeds), tannins and colour.
• The stems also help to break up the mass of grape skins, providing channels for the juice to drain.

Question 12

What are the disadvantages of whole-bunch pressing?

Answer 12

• Only possible if grapes have been manual-harvested
• Whole bunches take up more room in the press, therefore fewer grapes can be added for each press cycle.

Question 13

What is free-run juice?

Answer 13

The juice that can be drained off as soon as the grapes are crushed

Question 14

What is the difference in free run and press juice?

Answer 14

Free run juice has lower solids, tannin and colour, lower PH and higher acidity.
Press juice has lower acidity and less sugar. More solids, tannin and colour increase with more pressure of press.

Question 15

What are the disadvantages of soley using press juice for the production of wine?

Answer 15

Reduces the final volume of wine that can be produced and therefore has a cost implication.

Question 16

What is hyperoxidation?

Answer 16

The technique of deliberately exposing the must to large quantities of oxygen before fermentation.

Question 17

What are the aims of hyperoxidation in white winemaking?

Answer 17

• To produce wines that are more stable against oxidation after fermenation
• To help remove bitter compounds that can come from unripe grape skins, seeds and stems.

Question 18

Does hyperoxidation cause browning in white wines?

Answer 18

As the compounds oxidise, they turn brown. However during fermentation the compounds precipitate, returning the wine to its normal colour.

Question 19

What white wines is hyperoxidation not suitable for? Why?

Answer 19

Hyperoxidation is not suitable to aromatic or herbaceous varieties. The process can destroy some of the most volatile aroma compounds found in the must.

For example, hyperoxidation can reduce the levels of volatile thiols and methoxypyrazines found in Sauvignon Blanc, and therefore would not be carried out if an aromatic fruity or herbaceous style of this wine was desired.

Question 20

What are the costs associated with hyperoxidation?

Answer 20

• Equipment is not expensive
• As an extra step in the winemaking process, it requires labour to set up and monitor.

Question 21

When does clarification typically occur in white winemaking?

Answer 21

Between pressing and fermentation (clarification of must)
After fermentation

Question 22

What is the aim of must clarification in white wines?

Answer 22

• To reduce the amount of suspended solids including grape skin, stems and seeds.
• Winemakers will generally aim for the proportion of solids in the must to be 0.5–2%. (Some winemakers choose to leave 1-2% for added texture and complexity.)

Question 23

What are the possible results of leaving high levels of solids after must clarification in white winemaking?

Answer 23

• Some winemakers choose to leave around 1-2% solids to add texture to the wine (subtle astringency) and greater aromas from fermentation (greater complexity).
• Various compounds within the solids and their reactions can lead to off-flavours. (eg, reduction in high amounts).

Question 24

What are the risks of over-clarifying must in white wines?

Answer 24

A small amount of solids is beneficial in that it provides nutrients for yeast, and over-clarifying the must can lead to stuck fermentations. Fermentations with a very low level of solids also need careful management, and yeast nutrients (such as DAP) may need to be added.

Question 25

What are the four main methods of must clarification in white winemaking?

Answer 25

• Sedimentation
• Flotation
• Centrifugation
• Clarifying agents

Question 26

At what temperature is white must chilled to for sedimentation? Why?

For must clarification

Answer 26

The must is commonly chilled to around 4°C to reduce the rate of oxidation and the threat from spoilage organisms, and to avoid a spontaneous fermentation.

Question 27

How does the size and shape of the vessel influence the rate of sedimentation of must?

Must clarification in white wines.

Answer 27

It takes longer in large, tall vessels than in smaller, shorter vessels due to the depth over which the solids need to fall

Question 28

How does temperature influence the rate of sedimentation of must?

Must clarification in white wines.

Answer 28

Sedimentation at low temperatures slows microbial activity and reduces oxidation but takes longer, tying up tank space. Sedimentation times of 12–24 hours are not uncommon.

Question 29

Outline the steps of sedimentation in the clarification of musts.

Answer 29

1. Must is chilled (most commonly to around 4°c to reduce the rate of oxidation and microbial spoilage).
2. Suspended matter falls over time (typically 12-24 hours) with gravity.
3. The clear juice is transferred to the fermentation vessel, leaving solids behind (racking).
4. The solids left behind will often be filtered by cross flow or depth filters to extract extra juice.

Question 30

What is flotation?

Answer 30

A method of must clarification where a gas is bubbled up through the must, bringing solids to the top where they are skimmed off.

Question 31

Outline the steps of flotation.

Answer 31

• Fining agents are added to the must to help bind the particles together
• Gas is bubbled up through the must (inert, such as nitrogen; or oxygen, as a form of hyperoxidation).
• As the bubbles of gas rise, they bring with them the solid particles.
• The solid particles are then skimmed off the top of the vessel.

Question 32

What are the advantages of flotation as a technique for must clarification?

Answer 32

• It is effective and quick
• It can either be used as a continuous or a batch process
• The must does not need chilling, therefore saving on energy costs

Question 33

What are the costs associated with flotation?

Answer 33

Gases, fining agent and equipment

Question 34

What is a centrifuge?

Answer 34

A centrifuge is a machine that comprises a rapidly rotating container which uses centrifugal force to separate solids from liquids.

Question 35

What are the advantages of using centrifugation as a must clarification technique?

Answer 35

Centrifuges clarify the must quickly. They are used continuously (rather than as a batch process) which also saves time and labour costs.

Question 36

What are the disadvantages of centrifugation for must clarification?

Answer 36

Centrifiges are expensive to buy, and therefore are typically only used in wineries needing to process large volumes of must quickly.
They also increase the must’s exposure to oxygen unless the machine is flushed with inert gas, but that has an implication on costs.

Question 37

True or false

Flotation can be used on must as well as wine.

Answer 37

False
Flotation is a must clarification technique that can only be used on must

Question 38

What are pectins?

Answer 38

Pectins are naturally found in plant cell walls (in jam-making they are the compounds that turn liquid juice into gel).

Question 39

What is used to break down pectins in must?

Answer 39

Pectolytic enzymes

Question 40

Why might a winemaker add pectolytic enzymes to the must?

Answer 40

Pectolytic enzymes break down pectins in the must, allowing a more rapid separation between the liquid juice and solids. This speeds up the rate of sedimentation when clarifying must.

Question 41

True or false.

Pectolytic enzymes can be added to both must and wine as a method of clarification.

Answer 41

False.

Question 42

At what temperatures are white wines typically fermented at?

Answer 42

15°C for fruitier wines
17°C and sometimes higher where fruity flavours are not desired.

Question 43

Why are cooler fermentation temperatures better for the production of fruity wine wines?

Answer 43

The volatile aroma and flavour compounds that are desired in many white wines, for example, many esters, are best produced and retained at cool temperatures (around 15°C)

Question 44

Why would a winemaker choose to ferment their white wines at slightly higher temperatures than usual?

Answer 44

If fruity aromas are not desirable. For example, where oak will contribute many aromas.

Fermenting at slightly higher temperatures (17°C and sometimes higher) will promote yeast health and avoid the production of certain esters, such as isoamyl acetate (banana-like smell).

Question 45

What are the advantages of fermenting white wines in small oak barrels?

Answer 45

• Deeper colour and fuller body due to oxidative environment
• More integrated oak derive aromas due to the action of yeast during fermentation
• Increased contact between the wine and yeast lees; thought to contribute texture.
• More blending options; the wine in each barrel may be slightly different after the fermentation process.

Question 46

What white grape varieties is malolactic conversion not suitable for?

Answer 46

Winemakers typically avoid MLF for aromatic grape varieties to preserve the primary fruit flavour, despite them usually being high acid varieties.

Question 47

What is bâttonnage?

Answer 47

The stirring of the lees

Question 48

What is the most traditional of lees stirring/bâttonnage?

Answer 48

A rod is used to manually stir the lees into the wine

Question 49

What is the result of lees stirring/bâtonage?

Answer 49

• Increases oxygen exposure due to the need to remove the bung hole. This reduces reductive aromas.
• Increases lees aromas and decreases fruity aromas
• Improves mouthfeel by introducing yeast proteins and other products from autolysis.

Question 50

How can a winemaker mix the lees without exposing the wine to oxygen?

Answer 50

Barrel racks that permit easy rolling of the barrels