Specific Options for White Winemaking Flashcards
Explain transportation to winery and grape reception?
SKIN CONTACT
Skin contact is the process of leaving the juice in contact with the skins to extract compounds from the skins (similar to cold soaking in red winemaking). When carried out on (crushed) white grapes, the main purpose is 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. However, it is not a technique that is suited to all styles of wines and, if used too excessively, this technique can make white wines taste bitter and feel coarse in the mouth.
The majority of white wines are made with zero or minimal skin contact. The grapes are crushed and then pressed immediately (or whole bunches
of grapes are pressed without prior crushing). This is because the principle aroma and flavour compounds of white grapes are in the pulp. The grapes are crushed, the free run juice is drained off and the remaining grape mass is sent to the press. To further limit the contact between the juice and the skins, and reduce risk of oxidation, some winemakers choose to load the press with whole bunches of uncrushed grapes.
Minimal skin contact is typical for wines where delicate fruity flavours, minimal colour and a smooth mouthfeel are desired. It is also typically the choice for wines that are designed to be drunk early because the tannins that would be extracted during skin contact would not have time to soften. In addition, keeping skin contact to a minimum is the usual choice if fruit is at all under-ripe, as skin contact can extract bitter flavours and astringent tannins. A period of skin contact also slows processing and is another winemaking procedure that requires use of equipment and labour. It is therefore less likely to be carried out on inexpensive wines from a logistics and cost perspective.
Because skin contact maximises flavour extraction, it is most effectively used on aromatic grape varieties that have lots of aroma compounds that can be extracted, such as Riesling, Gewurztraminer, Viognier, Muscat and Sauvignon Blanc. In these aromatic varieties that often are not matured in oak, it is also a way of enhancing texture. However, there are some winemakers that feel that the technique leads to homogenisation, reducing the variations between grape varieties and different vineyard sites.
Explain pressing the grapes?
In white winemaking, the grapes are almost always pressed to separate the skins from the juice before fermentation. Typically, pressing will be as gentle as possible to avoid the extraction of unwanted compounds from the skins and seeds of the grapes, such as tannins and colour.
An important choice involves whether to destem the grapes before pressing. Usually, grapes are destemmed and crushed before being loaded into the press. However, it is also possible to press whole bunches of grapes. This 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 also 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.
However, this method of pressing is only an option if the grapes have been hand-harvested. Additionally, the whole bunches take up a lot of room in the press, therefore fewer grapes can be loaded within each press cycle. Whole bunch pressing may be suitable when making smaller batches of premium wines, but is less likely to be an option when making large volumes of inexpensive and mid-priced wines where grapes need to be processed quickly and efficiently.
On the choice of the press to be used, see Pressing in General Winemaking Options.
If grapes are destemmed and crushed, the juice that can be drained off as soon as the grapes are crushed is called the free run juice. This is typically the juice that is lowest in solids, tannin and colour. The winemaker may choose to make wine from entirely free run juice. However, using only this proportion of the juice reduces the final volume of wine that can be produced and therefore has a cost implication.
The juice that runs off through the pressing is called the press juice. At the start, the press juice will be similar to the free run juice, but, as the pressing continues and more pressure is applied, more solids, tannin and colour are extracted. The press juice also has lower acidity and less sugar than the free run juice, and typically makes wines that are fuller bodied (compared to those from the free run juice). The winemaker may decide to separate the press juice into different fractions (called ‘press fractions’) as the pressing continues. Different press fractions may be blended later in the winemaking and maturation process. The last press fractions are likely to be too astringent or bitter (due to phenolic compounds from the skins, seeds or stems) and therefore will be discarded.
What is hyperoxidation?
Hyperoxidation is the technique of deliberately exposing the must to large quantities of oxygen before fermentation. This targets the compounds in the must that oxidise most readily. As they oxidise, these compounds turn the must brown. However, during fermentation the compounds precipitate, returning the wine to its normal colour. The main aim is to produce wines that are more stable against oxidation after fermentation. This process can also help to remove bitter compounds that can come from unripe grape skins, seeds and stems. Hyperoxidation can destroy some of the most volatile aroma compounds found in the must and therefore is typically better suited to neutral grape varieties such as Chardonnay. 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.
The equipment required for hyperoxidation is not particularly expensive, but it is an extra step in the winemaking process that requires labour to set up and monitor, and therefore overall it may have some small impact on costs.
Explain clarification of must?
Between pressing and fermentation, the juice of white grapes may be clarified. (Clarification may also occur after fermentation and this is covered in Post-Fermentation Clarification
in Finishing and Packaging.) The aim of clarification is to reduce the amount of suspended solids within the must. These solids include particles of grape skin, stem and seeds.
Winemakers will generally aim for the proportion of solids in the must to be 0.5–2 per cent. Some winemakers choose to retain higher proportions of solids, and may not clarify the must at all because this can add to the texture of the wine, giving a subtle astringency (particles of skin and stem will add tannins). Relatively high levels of solids can also give a greater range of aromas from fermentation, which could give greater complexity; however, lower levels of solids are better for obtaining fruity aromas. Therefore, a relatively high level of solids may be desirable for a premium-priced Chardonnay, but would be less suitable for an inexpensive Pinot Grigio. Fermentations with a high level of solids need careful monitoring and management as the various compounds within the solids and their reactions can lead to off-flavours. For example, high solids fermentations can give reductive sulfur compounds that at low levels may be desirable (struck match, smoke), but at higher levels are very negative for quality (aromas of rotten eggs). It is therefore a technique better suited to small-volume, premium production.
However, 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.
There are many different options for the clarification of grape must.
What is sedimentation?
Sedimentation is the simplest form of clarification. It is also sometimes called ‘settling’. The suspended solids in the must are left to fall over time with gravity. The must is commonly chilled to around 4°C (39°F) to reduce the rate of oxidation and microbial spoilage, and to avoid a spontaneous fermentation. The rate of sedimentation will also depend on the size and shape of the vessel; it takes longer in large, tall vessels than in smaller, shorter vessels due to the depth over which the solids need to fall. Sedimentation times of 12–24 hours are not uncommon. The clear juice is transferred to the fermentation vessel, leaving the sediment of solids at the bottom of the sedimentation vessel (a process called racking, see The Role of Lees in Still Wine Maturation). The solids left behind after sedimentation will often be filtered by cross flow or depth filters to extract extra juice.
Sedimentation can be used to clarify wines as well as must. Sedimentation is the cheapest method in terms of equipment required and is the most traditional way to clarify must or wine in that it requires no extra equipment or additives. However, it takes the most time and there is a cost to the energy used in chilling. It is also a batch process, which, again, costs in labour and time. For these reasons, it is most commonly used for small-volume production of premium wines.
What is flotation?
Flotation involves bubbling gas up through the must. 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.
Compared to sedimentation, flotation speeds up the rate of clarification. Inert gas such as nitrogen is typically used. If oxygen is used as the gas, this is a method of hyperoxidation. Fining agents must be added to the must for this technique to be successful (to help bind the particles together), and it can it only be used on must, not wine. This technique is a little more expensive than sedimentation in terms of the equipment needed; however, it is effective and quick, and can either be used as a continuous or a batch process. The technique requires gases, fining agents and equipment for bubbling the gas through the liquid. However, the must does not need chilling, and therefore there is a saving on energy costs.
What is centrifugation?
A centrifuge is a machine that comprises a rapidly rotating container which uses centrifugal force to separate solids from
liquids. The advantage of centrifuges is that they clarify the must quickly. They are used continuously (rather than as a batch process) which, again, saves time and labour costs. However, they 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. Centrifuges can be used on wine as well as must.
Explain clarifying agents?
A number of 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 (in jam-making they are the compounds that turn liquid juice into gel). Breaking down the pectins allows a more rapid separation between the liquid juice and solids. Pectolytic enzymes only aid the clarification of must, not wine. Some fining agents can aid clarification of both must and wine. There is a cost of purchasing these agents, but this may be justified against the time and energy saved compared to sedimentation (where the wine would need to be chilled to low temperatures for several hours).
Explain fermentation temperatures and vessels for white wines?
Fermentation temperatures for white wines are typically cooler than those used in red winemaking. This is because the volatile aroma and flavour compounds that are desired in many white wines are best produced and retained at cool temperatures (around 15°C / 59°F).
In some styles of white wines, fruity aromas are not particularly desired; for example, where oak is going to be used to provide flavours. In these
cases, the fermentation can be slightly warmer (17–25°C / 63–77°F and sometimes higher) to promote yeast health and avoid the production of certain esters, such as isoamyl acetate (banana-like smell).
Stainless steel tanks are the most popular choice for fruity, floral white wines, such as many styles of Sauvignon Blanc and Veneto Pinot Grigio, due to the ability to control temperatures easily and hence maintain the cool fermentation conditions needed for these styles of wine. Concrete and old oak vats (as well as stainless steel tanks) may be used for white wines fermented at slightly warmer temperatures, where maximising the fruity and floral aromas from fermentation is not the aim (for example, some styles of Chablis and white Rioja).
Small oak barrels (sometimes new oak) are a popular choice for some styles of white wine, particularly premium and super-premium Chardonnay (due to the high costs of new barrels). For a full introduction to the use of oak in fermentation, see Alcoholic Fermentation in General Winemaking Options. Monitoring fermentation in these small vessels is more labour intensive than monitoring a single large vessel. However, it is thought that wines which have been fermented in small oak vessels have a deeper colour and fuller body, due to the oxidative environment, and more integrated oak-derived aromas, due to the action of the yeasts during fermentation (compared to wines that are fermented in steel or concrete and later transferred to an oak barrel for maturation). The small size of these vessels also increases the contact between the wine and yeast lees, and this is also thought to contribute texture. These vessels can also provide more blending options because the wine in each barrel may be slightly different after the fermentation process.
As with oak maturation, small barrel fermentation less likely to be used for wines made from aromatic grape varieties such as Riesling where the winemaker is usually looking to preserve primary aromas and flavours from the grapes and avoid the characteristics of oak.
Explain malolactic conversion for white wines?
The effects of malolactic conversion are a reduction in acidity, increase in microbiological stability and a modification to the flavours of wine. In white wines, the winemaker typically makes a conscious choice whether or not to put the wine through malolactic conversion because the effects on the final wine make a significant difference to the style.
With a low-aromatic variety such as Chardonnay, there is a choice between the perceived greater complexity of wines that have been through malolactic conversion and the primary fruit character of those that have not. By contrast, with aromatic varieties such as Riesling or Sauvignon Blanc, malolactic conversion is typically avoided to preserve the primary aromatics, despite these being high acid varieties. In this way, the distinctive aromatics of the individual varieties is maintained.
Malolactic conversion will decrease the acidity and increase the pH of the wine. It is possible to adjust the acidity of the wine as necessary (this adjustment can also be made at the must stage). It is also possible for winemakers to reduce the alcohol of the wine at this stage.
Explain barrel maturation for white wine?
Whether to mature the wine in wood and the details of this process will have a significant impact on the style and price of white wines. The options regarding maturation in wood can be found in General Winemaking Options. Premium and super-premium wines, particularly those made with low-aromatic varieties such as Chardonnay, are likely to be aged in small oak barrels for the texture and complexity of flavours this can bring. However, for wines made from aromatic grapes, such as Riesling, the vanilla and toasty flavours from the oak and nutty flavours from slow oxidative ageing are often not desirable. Maturation in oak barrels is usually too costly for inexpensive wines and therefore, if any flavours from oak are wanted, this may come from oak alternatives such as staves.
Explain lees ageing for white wines?
The aims of ageing on the lees are to give more body, soften the mouthfeel and help to stabilize the wine. They also protect the wine from oxygen and may introduce some reductive sulfur compounds, which, at low levels, some winemakers and consumers consider desirable (aromas such as struck match, smoke). The impact of lees is thought to be more significant in white wines than red wines. It is common for a range of white wine styles and prices, but is less practiced on inexpensive wines, which will usually be released from the winery for sale as soon as possible.
The lees may or may not be stirred to unsettle it from the bottom of the vessel and mix it in the wine. Lees stirring is sometimes referred to by the French term, bâtonnage. Lees stirring can increase the release of yeast compounds into the wine. The most traditional method of lees stirring for wine stored in small vessels such as barrels, is to use a rod and manually stir the lees into the wine. Due to the need to remove the bung from the vessel, this method increases oxygen exposure and can result in an increase in the effects from the dead yeast and a decrease in fruity flavours. The introduction of oxygen and disturbing of the lees also reduces the development of reductive sulfur compounds and the off-aromas that they can introduce if not appropriately managed. However, there are other options that now agitate and/or mix the lees without needing to open the vessel (for example, barrel racks that permit easy rolling of the barrels). This can give the winemaker more options and therefore more control over the impact of lees and oxygen. Lees stirring on large numbers of large barrels is labour intensive and can therefore add to the cost of production.
