Specific options for white winemaking Flashcards
The process of skin contact in white wines
The process of leaving the juice in contact with the skins to extract compounds from the skins
For white wines, the purpose is to enhance the extortion of aroma and flavour compounds and precursor and to enhance the texture of the wine by extracting a small amount of tannin
Not suited for all styles of wine, and if used too excessively white wines can taste bitter and feel coarse in the mouth
White wine styles with/without skin contact
The majority of white wines are mede with zero or minimal skin contact
Minimal skin contact is typical for wines where delicate fruit, minimal colour and a smooth mouthfeel is desired and is also typical for wines for early drinking, as tannins would not have the time to soften
Keeping skin contact to a min is also the usual choice when fruit is un-ripe, as skin contact will extract bitter/green flavours and astringent tannins
A period of skin contact requires time, equipment and labor and is therefore usually not carried out on inexpensive wines, from a cost perspective
The influence of skins contact on flavour extraction
Skin contact maximizes flavour extraction, and is most effectively used on aromatic varieties; Gewurz, Riesling, Viognier, Muscat.
In these aromatic varieties that often are not matured in oak, it is also a way of enhancing texture
Some winemakers believe this technique leads to homogenization, reducing the variations between grape varieties and vineyards sites
The influence of time and temp on skin contact
Time and temp are key factors that can influence extraction during skin contact
Times can range from 1 hour to 24 hours and over, with longer time on the skins, with greater extraction of flavour and tannins
Chilling during the time reduces the rate of extraction of flavour and tannins, permitting more control and reduces the rate of oxidation and microbial spoilage
The juice is typically chilled down to 15
Wine is usually pressed to separate the skins and juice before fermentation starts
Orange wine
At the extreme end of the spectrum, there are some wines made from white grapes that are fermented on their skins, without temp control or sulfur additions
The wines are often amber colored, which developed due to the oxidation of compounds extracted from the grape skins
Do not taste like typical wines, usually dry, notable levels of tannins and taste mainly tertiary (nuts, dried fruit)
Pressing
In white winemaking grapes are almost alway pressed to separate the skins from the juice before fermentation
Typically as gentle as possible to avoid the extraction of unwanted compounds from the skins and seeds such as tannins and colour
Destemming
Usually grapes are destemmed and crushed before pressing
Whole bunch pressing is also possible, reduce chance of oxidation before and during pressing, especially when inert gases are used within the press. Also the most gentle form of pressing, providing juice low in solids, tannin and colour
Whole buch pressing is only possible when grapes are hand harvested and take a lot of room up in the press, fewer grapes can be loaded within each press. Suitable for smaller batches of premium wines, less likely for inexpensive wines which requires quick and efficient processing of grapes
Free run juice
De juice that can be drained off as soon as the grapes are crushed, typically the lowest in solids, tannin and colour
The winemaker may choose to make wine entirely from free run juice only. However, it reduces the final volume of wine that can be produced and has cost implications
Press juice
Juice that runs off through the pressing of grapes
At the start, similar to free run juice, but as pressing continues and more pressure is applied, more solids, tannins and colour is extracted
Lower acidity and less sugar than the free run juice, and typically make wines that are fuller bodied
Press juice may be separated into different fractions (press fractions) as the pressing continues and different fractions may be blended later in the winemaking and maturation process
The last press fractions are likely to be too astringent or bitter and therefore will be discarded
Hyperoxidation
A technique whereby the must is exposed to large quantities of oxygen before fermentation on purpose. Targets the compounds in the must that oxide most readily
As these compounds oxidize, they turn the must brown. But, during fermentation the compounds precipitate, returning the wine to its normal colour
The aim is to produce wines that are more stable against oxidation after fermentation and also helps to remove bitter compounds deriving from unripe grapes, seeds and skins
It can destroy volatile aroma compounds in the must and is therefore more suitable to neutral varieties such as Chardonnay.
For example; reduces volatile thiols and methoxypyrazins ins Sauvignong Blanc, and would therefore not be carried out if an aromatic of herbaceous style is desired
Equipment is not expensive, but extra step in the process requiring labour and therefore has an impact on the costs
Clarification of the must
Juice may be clarified prior to fermentation to reduce the amount of suspended solids within the must (skin, seeds, stem)
Generally a proportion 0.5-2% solids in the must
Some retain higher proportions of solids, and may not clarify the must because they believe it will add texture and can also give a greater range of aromas from fermentation, adding complexity
However, lower levels are better to obtaining fruity aromas therefore more suitable for a premium Chardonnay and less for a inexpensive pinot Grigio
Ferments with high levels of solid particles need careful monitoring because compounds within the solids and their reactions during fermentation can lead to off-aromas
High solids in fermentations can give reductive sulfur compounds which at low levels may be desirable (smoke, struck match), but undesirable at higher levels (rotten egg)
However, a small amount is beneficial as it provides nutrients for yeas and over clarifying the must can leas to stuck ferments
Different options for clarifying the must prior to fermentation are;
- Sedimentation
- Flotation
- Centrifugation
- Clarifying agents
Sedimentation
Simplest form of clarification (settling)
The solids in the must are left to fall over time with gravity
Must is chilled to around 4 degrees to reduce the risk of oxidation and microbial spoilage, and to avoid spontaneous fermentation
The rate of sedimentation will depend on the size of the vessel; takes longer in large, tall vessel than in smaller, shorter vessels due to the depth over which the solids need to fall. 12-24 hours is not uncommon
Clear juice is transferred to the fermentation vessel, leaving sediment at the bottom of the sedimentation vessel (called racking)
Sediment left behind is often filtered by cross flow (absolute) or depth filters to extract extra juice
Cheapest in terms of equipment and most traditional form of clarifying must or wine (nog equipment required) but, it takes the most time, and there is a cost of energy used in chilled as well as the labour costs
Most common for small volume production of premium wine
Flotation
Involves bubbling gas up through the must. Inert gas such as nitrogen is typically used, if oxygen is used it is a form of hyperoxidation
As the bubbles of gas rise, they bring with them the solid particles with are then skimmed off the top of the vessel. Fining agents must be added to the must for this technique to be successful, and can only be used on must (prior fermentation) and not wine
Compared to sedimentation, it speeds up the rate of clarification
Little more expensive than sedimentation in terms of equipment, but its effective and quick. The technique also requires gases, fining agents. But, does not require chilling the must, saving on energy costs
Centrifugation
A machine that comprises a rapidly rotating container which uses centrifugal force to separate solids from the must and clarifies quickly
Used continuously which saves time and labour costs
Expensive to buy, typically only used in wineries needing to precess large volumes of must very quickly
They also increase the must’s exposure to oxygen unless the machine is flushed with inert gas, which has cost implications
Can be used on must as well as wine
Clarifying agents
Can be added to speed up the process of sedimentation
Pectolytic enzymes break down pectins in the must
Pectins are naturally found in plant cell wall, breaking down pectins allows a more rapid separation between the liquid and the solids
Only aid the clarification of must, not wine
There is a cost of purchasing these agents, but this may justify the time and energy saved compared to sedimentation
