16. Specific Options for White Winemaking Flashcards
What is the purpose of skin contact for white wines?
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.
Why are most white wines not subjected to skin contact?
The principal aroma and flavour compounds of white grapes that are desirable in white wines are in the pulp.
What are the reasons a winemaker would subject their white wines to minimal or no skin contact?
- 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.
What grape varieties is skin contact most effectively used? Why
Aromatic grape varieties such as Riesling, Gewurtztraminer, Muscat and Sauvignon Blanc.
These have lots of aroma compounds that can be extracted from the skins.
What are the two key factors that influence extraction during skin contact in white wines?
Time
Temperature
How long does skin contact last for in white wine production?
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.
At what temperature are white wines kept during skin contact? Why?
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.
When does skin contact for white wines usually occur?
After crushing
Before pressing and fermentation
What are orange/amber wines?
White wines that have been fermented on their skins.
How do orange wines differ in structure and flavour than white wines?
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.
Why might a winemaker choose to press whole bunches of white grapes?
- 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.
What are the disadvantages of whole-bunch pressing?
- 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.
What is free-run juice?
The juice that can be drained off as soon as the grapes are crushed
What is the difference in free run and press juice?
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.
What are the disadvantages of soley using press juice for the production of wine?
Reduces the final volume of wine that can be produced and therefore has a cost implication.
What is hyperoxidation?
The technique of deliberately exposing the must to large quantities of oxygen before fermentation.
What are the aims of hyperoxidation in white winemaking?
- 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.
Does hyperoxidation cause browning in white wines?
As the compounds oxidise, they turn brown. However during fermentation the compounds precipitate, returning the wine to its normal colour.
What white wines is hyperoxidation not suitable for? Why?
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.
What are the costs associated with hyperoxidation?
- Equipment is not expensive
- As an extra step in the winemaking process, it requires labour to set up and monitor.
When does clarification typically occur in white winemaking?
Between pressing and fermentation (clarification of must)
After fermentation
What is the aim of must clarification in white wines?
- 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.)
What are the possible results of leaving high levels of solids after must clarification in white winemaking?
- 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).
What are the risks of over-clarifying must in white wines?
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.
What are the four main methods of must clarification in white winemaking?
- Sedimentation
- Flotation
- Centrifugation
- Clarifying agents
At what temperature is white must chilled to for sedimentation? Why?
For must clarification
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.
How does the size and shape of the vessel influence the rate of sedimentation of must?
Must clarification in white wines.
It takes longer in large, tall vessels than in smaller, shorter vessels due to the depth over which the solids need to fall
How does temperature influence the rate of sedimentation of must?
Must clarification in white wines.
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.
Outline the steps of sedimentation in the clarification of musts.
- Must is chilled (most commonly to around 4°c to reduce the rate of oxidation and microbial spoilage).
- Suspended matter falls over time (typically 12-24 hours) with gravity.
- The clear juice is transferred to the fermentation vessel, leaving solids behind (racking).
- The solids left behind will often be filtered by cross flow or depth filters to extract extra juice.
What is flotation?
A method of must clarification where a gas is bubbled up through the must, bringing solids to the top where they are skimmed off.
Outline the steps of flotation.
- 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.
What are the advantages of flotation as a technique for must clarification?
- 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
What are the costs associated with flotation?
Gases, fining agent and equipment
What is a centrifuge?
A centrifuge is a machine that comprises a rapidly rotating container which uses centrifugal force to separate solids from liquids.
What are the advantages of using centrifugation as a must clarification technique?
Centrifuges clarify the must quickly. They are used continuously (rather than as a batch process) which also saves time and labour costs.
What are the disadvantages of centrifugation for must clarification?
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.
True or false
Flotation can be used on must as well as wine.
False
Flotation is a must clarification technique that can only be used on must
What are pectins?
Pectins are naturally found in plant cell walls (in jam-making they are the compounds that turn liquid juice into gel).
What is used to break down pectins in must?
Pectolytic enzymes
Why might a winemaker add pectolytic enzymes to the must?
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.
True or false.
Pectolytic enzymes can be added to both must and wine as a method of clarification.
False.
At what temperatures are white wines typically fermented at?
15°C for fruitier wines
17°C and sometimes higher where fruity flavours are not desired.
Why are cooler fermentation temperatures better for the production of fruity wine wines?
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)
Why would a winemaker choose to ferment their white wines at slightly higher temperatures than usual?
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).
What are the advantages of fermenting white wines in small oak barrels?
- 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.
What white grape varieties is malolactic conversion not suitable for?
Winemakers typically avoid MLF for aromatic grape varieties to preserve the primary fruit flavour, despite them usually being high acid varieties.
What is bâttonnage?
The stirring of the lees
What is the most traditional of lees stirring/bâttonnage?
A rod is used to manually stir the lees into the wine
What is the result of lees stirring/bâtonage?
- 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.
How can a winemaker mix the lees without exposing the wine to oxygen?
Barrel racks that permit easy rolling of the barrels
