White Winemaking Options Flashcards
Describe how skin contact is used in white winemaking
Skin contact is the process of leaving juice in contact with skins to extract compounds from skins (similar to cold soaking in red winemaking).
When carried out on crushed white grapes, main purpose is to enhance extraction of aroma and flavour compounds and precursors, and enhance texture of wine by extracting a small amount of tannin.
Skin contact maximizes flavour extraction - used most commonly on aromatic varieties - Riesling, Gewurz, Viognier, Muscat, Sauvignon Blanc
Juice usually chilled to below 15C. Chilling juice reduces rate of extraction of flavours and tannins, permitting more control, and reduces rate of oxidation and threat from spoilage organisms, including likelihood of spontaneous fermentation.
Time range from 1-24 hours - greater time on skins leads to greater extraction of flavour and tannins.
Describe what free-frun juice is
If grapes are destemmed and crushed, juice can be drained off as soon as grapes are crushed - this is called free run juice.
Juice that is lowest in solids, tannin and colour. Lower in pH and higher in acidity.
Winemaker may choose to make wine entirely from free run juice if looking to make lighter bodied style of wine and minimize any colour or tannin.
Using only a proportion of juice reduces final volume of wine that can be produced and has cost implications.
Describe the process of pressing in white winemaking
In white winemaking, grapes almost always pressed to separate skins from juice before fermentation. Pressing is as gentle as possible to avoid extraction of unwanted compounds from skins and seeds (tannins, colour).
Important choice is whether to destem grapes before pressing. They are usually destemmed and crushed before being loaded into press.
Can press whole bunches of grapes - reduces chance of oxidation, especially if inert gases (nitrogen, carbon dioxide or dry ice, are used within press) One of gentlest forms of pressing - provides juice low in solids, tannins and colour.
Describe what press fractions are
Juice that runs off through the pressing is called press juice.
At the start, press juice is similar to free run juice, but as pressing continues and more pressure applied, more solids, tannins and colour are extracted.
Winemaker may decide to separate press juice into different fractions called press fractions as pressing continues
Different press fractions may be blended with free run juice and can increase body and texture.
Last press fractions are likely too astringent or bitter (due to tannins from skins, seeds or stems) and will be discarded
Describe what hyperoxidation is
Hyperoxidation is a technique of deliberately exposing must to large quantities of oxygen before fermentation. It targets the compounds in the must that oxidize most readily. As they oxidize, the compounds turn brown. During fermentation the compounds precipitate, returning wine to its normal colour.
Aim is to produce wines that are more stable against oxidation after fermentation. Can help remove bitter compounds from unripe grape skins, seeds and stems.
It can destroy some volatile aroma compounds and better suited to less aromatic varieties. Can reduce volatile thiols and methoxypyrazines (Sauvignon Blanc).
Equipment not expensive, but extra step in winemaking process that requires labour to setup and monitor. Small impact on costs.
List the must clarifications that can be used in white winemaking
Potential alcohol
Acidification
Deacidification
Enrichment
Reducing Alcohol
Adding tannins
Describe clarification related to white winemaking
In white winemaking clarification is done between pressing and fermentation. The aim os to reduce the amount of suspended solids within must. Winemakers aim for proportion of solids in must to be 0.5-2%. Levels below 1% only achieved by using pectolytic enzymes or centrifugation.
Describe the clarification process called floatation
The floatation clarification process involves bubbling gas up through the must. As bubbles rise, they bring with them the solid particles. Solid particles are skimmed off the top of the vessel.
This speeds up rate of clarification compared to sedimentation.
Inert gas usually used (nitrogen). If oxygen used, this method is called hyperoxidation.
Fining agents need to be added to must for this technique to work.
Can only be used on must, not wine.
It is effective and quick, and can be used as a continuous or batch process.
Describe the clarifying agent pectolytic enzymes
Pectolytic enzymes break down pectins in must. Pectins are found in plant cell walls (jam making - compounds that turn liquid into gel)
Breaking down pectins allows more rapid separation between liquid juice and solids.
Only aid clarification for must, not wine.
There is a cost to purchasing - may be justified against time and energy saved compared to sedimentation.
Describe the temperature for alcoholic fermentation for white winemaking
Fermentation temps for white wines are cooler than those for red winemaking. Because volatile aroma and flavour compounds are desired in many white wines (esters), they are best produced and retained at cool temps (15C).
When fruit aromas aren’t desired, fermentation temps can be slightly warmer (17-25C) to promote yeast health and avoid production of certain esters (isoamyl acetate - banana-like smell).
Stainless steel tanks commonly used for fruity, floral white wines - can control temps easily and maintain cool fermentation conditions needed to enhance these aromas.
List the common vessels used in white winemaking
Stainless steel
Concrete
Oak
Plastic vessels
Teracotta
Describe how malolactic conversion is used in white winemaking
Effects of MLC are a reduction in acidity, increase in microbiological stability and modification of flavours of wine. In white wines, winemaker makes a conscious choice wether or not to put wines through MLC.
Low-aromatic variety (Chardonnay) - choice between perceived greater complexity of wines that have gone through MLC and primary fruit character of those that have not.
Aromatic varieties (Riesling, Sauv Blanc) - MLC usually avoided to preserve primary aromatics despite these being high acid varieties. Distinctive aromas are maintained.
Describe how barrel maturation is used for white wines
Maturing wine in wood has significant impact on style and price of white wines.
Premium and super-premium wines, particularly those made with low-aromatic varieties (Chardonnay), are likely to be aged in small oak barrels for texture and complexity of flavours.
For aromatic wines, the vanilla and toasty flavours from oak and nutty flavours from slow oxidative ageing are often not desirable.
Maturation in oak usually too costly for inexpensive wines - if flavours from oak wanted, this may come from oak alternatives.
Describe how lees ageing is used for white wines
Aim of ageing on lees are to give more body, soften mouthfeel and help stabilize the wine. They also protect wine from oxygen and may introduce reductive sulfur compounds - at low levels may be desirable.
Impact of lees thought to be more impactful on white wines than red wines. It is common for range of white wine styles and prices. Less practiced on inexpensive wines.
Describe the lees stirring process
Lees may or may not be stirred to unsettle it from the bottom of the vessel and mis it in the wine. Lees stirring french term is batonnage.
Lees stirring can increase the release of yeast compounds in wine.
Most common method is to use a rod and manually stir the lees into the wine. Bung whole needs to be removed so this Increases oxygen exposure and can result in increase in the effects from dead yeast and decrease in fruity flavours.
