Specific Options for White Winemaking

Question 1

Specific white winemaking

Skin contact

Answer 1

Process of leaving the juice in contact with the skins to extract compounds:
- Enhance the extraction of aroma and flavour compounds and precursors = most effectively used on aromatic grape varieties
- Enhance the texture of the wine by extracting a small amount of tannin (useful when oak maturation is avoided)
- Not a technique that is suited to all styles of wines (the principal aroma and flavour compounds of white grapes are in the pulp)
- Times can range from around an hour to 24 hours and over
- Chilling the juice during this time reduces the rate of extraction of flavours and tannins and reduces the rate of oxidation and the threat from spoilage organisms, including likelihood of a spontaneous fermentation (typically >15°C )

• To further limit skin contact and reduce risk of oxidation = whole bunch pressing
• Minimal skin contact is typical for wines where delicate fruity flavours, minimal colour and a smooth mouthfeel are desired.
• Typically the choice for wines that are designed to be drunk early (tannins wouldn’t have time to soften)
• Usual choice if fruit is at all under- ripe, as skin contact in this case could extract bitter flavours and astringent tannins.
• More costly, time consuming and labour intensive
• Can also be fermented on their skins, as with red grapes. The resulting wines are usually termed ‘orange wines’ or ‘amber wines’

Question 2

Specific white winemaking

Pressing the grapes

Answer 2

Almost always pressed to separate the skins from the juice before fermentation.
(as gentle as possible to avoid the extraction of unwanted compounds from the skins and seeds of the grapes, such as tannins and colour)

Whole bunch pressing:
- 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. - One of the gentlest forms of pressing, providing juice that is low in solids, tannins and colour
- The stems also help to break up the mass of grape skins, providing channels for the juice to drain
- fewer grapes can be loaded within each press cycle
- suitable when making smaller batches of premium wines

Destemmed and crushed grapes pressing:
- free run juice = drained off as soon as the grapes are crushed (lower in pH, colour, tannin and higher in acidity)
- Press juice = juice that runs off through the pressing (lower acidity and less sugar, more colour and tannins)

Question 3

Specific white winemaking

Hyperoxidation

Answer 3

Deliberately exposing the must to large quantities of oxygen before fermentation

• More stable against oxidation after fermentation
• Can destroy some of the most volatile aroma compounds found in the must and therefore is typically better suited to less aromatic grape varieties

Question 4

Specific white winemaking

Clarification of the must

Answer 4

Between pressing and fermentation, the juice of white grapes may be clarified to reduce the amount of suspended solids

Generally proportion of solids in the must to be 0.5–2% (below 1% only by using pectolytic enzymes or centrifugation)

1-2% can add texture
Relatively high levels = greater range of aromas from fermentation (greater complexity)
Lower levels = better for obtaining fruity aromas

Fermentations with a high level of solids need careful monitoring and management (can lead to off-flavours = reductive flavours)

Solids provides nutrients for yeast = over-clarifying the must can lead to stuck fermentations (yeast nutrients, such as DAP may need to be added)

Question 5

Specific white winemaking

Options for clarification of the must:

Answer 5

Sedimentation: (“settling”)
- Simplest form of clarification
- Must commonly chilled to around 4°C (39°F) to reduce the rate of oxidation and the threat from spoilage organisms, and to avoid a spontaneous fermentation
- Rate of sedimentation depend on the size and shape of the vessel
- Usually around 12-24h
- Time and labour costly = suitable for small-volume production of premium wines
- batch process

Flotation:
- Involves bubbling gas up through the must (usually Nitrogen)
- 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.
- Fining agents must be added to the must for this technique to be successful (to help bind the particles together)
- Can only be used on must, not wine
- can be continuous or batch process

Centrifugation:
- A centrifuge is a machine that comprises a rapidly rotating container which uses centrifugal force to separate solids from liquids
- Quick, continuous process
- Expensive to buy = suitable for large volumes wineries
- Increase the must exposure to oxygen unless the machine is flushed with inert gas (additional cost)
- Can be used on wine as well as must.

Clarifying agents:
- Different compounds can be added to the must as processing aids to speed up the rate of sedimentation.
- Pectolytic enzymes break down pectins in the must (Pectins are naturally found in plant cell walls) Breaking down the pectins allows a more rapid separation between the liquid juice and solids.
- Only used on must
- Some fining agents can aid clarification of both must and wine

Question 6

Specific white winemaking

Fermentation temperatures and Vessels for White Wines

Answer 6

Temperature:
- Cool temperature (around 15°C ): the volatile aroma and flavour compounds that are desired in many white wines (many esters) are best produced and retained at cool temperatures
- Slightly warmer (around 17-25°C ) for some wine styles like oak matured wines to promote yeast health and avoid the production of certain esters, such as isoamyl acetate (banana-like smell)

Vessel:
- stainless steel: ability to control temp easily = suitable for fruity, floral wines
- Concrete and old oak vats: for white wines fermented at slightly warmer temperatures
- Small oak barrels (sometimes new oak): deeper colour and fuller body, due to the oxidative environment / more integrated oak-derived aromas / increased contact with yeast lees = more texture

Question 7

Specific white winemaking

Malolactic conversion for White Wines

Answer 7

• Reduction in acidity / increse of PH
• increase in microbiological stability
• modification to the flavours of wine
• reduction of primary fruit character

Question 8

Specific white winemaking

Lees ageing for White Wines

Answer 8

• Increase body
• Soften the mouthfeel
• Help to stabilize the wine
• Protect from oxygen
• May introduce some desirable reductive sulfur compounds (struck match, smoke)

Bâtonnage = Lees stirring
- Can increase the release of yeast
compounds into the wine
- increases oxygen exposure = decrease in
fruity flavours
- alternative = rolling barrels (avoid opening the barrel = not oxydative)