D16: White Winemaking Flashcards
Why would you leave grapes in contact with the skin during white wine making?
enhance extraction of aroma and flavour compounds and precursors
enhance texture of wine by extracting small amount of tannin
*** carried out on crushed white grapes
Why would you NOT carry out skin contact during white wine making?
”- doesn’t suit all styles of wine
- can make wine seem coarse or bitter to taste
- most have zero or minimal skin contact
What is the process for skin contact in white wine making?
- grapes crushed and pressed
- whole bunches pressed and not crushed as want aroma and flavour compounds from pulp
- free run juice is drained off
- remaining grape mass sent to the press
- can load whole bunches of uncrushed grapes
** all of this is a winemaker choice
** whole bunches can reduce risk of oxidation
Why would a winemaker want minimal skin contact?
- want fruit flavours, minimal colour and smooth mouthfeel
- for early drinking wines (tannins wouldn’t have time to soften)
- if fruit is under-ripe (would extract bitter flavours and astringent tannins if did have contact)
- slow process requiring additional equipment and labour
What are the benefits of skin contact?
- maximises flavour extraction
- good for aromatic varieties with lots of aroma compounds to be extracted
What varieties benefit from skin contact?
- Riesling
- Gewurztraminer
- Viognier
- Muscat
- Sauvignon Blanc
(helps give these wines texture as they often aren’t matured in oak)
What are the negatives of skin contact?
- homogenisation
- can reduce variations between grape varieties and different vineyard sites
How long does skin contact take?
- ranges from an hour to 24 hours
- greater length of time on skins leads to greater extraction of flavour and tannins
What impact does temperature have on skin contact?
- chilling juice reduces rate of extraction and tannins
- chilled down to below 15 degrees
- then pressed to separate skins and juice before ferm begins
- reduces rate of oxidation and microbial spoilage
- reduces chance of spontaneous fermentation
What is orange wine?
- white grapes fermented on skins
- may undergo post-ferm maceration
- no temp control or sulfur
- name comes from colour of wines which develops due to oxidation of compounds extracted from grape skins
- don’t taste like white wines
- dry, notable level of tannins
- nuts and dried fruit
Grapes are almost always pressed to…
separate skins from juice before fermentation
Is pressing usually gentle or firm - why?
typically gentle pressing to avoid extraction of unwanted compounds from skins and seeds of grape (e.g. tannins and colour)
Destemming?
- important choice
- grapes normally destemmed and crushed before being loaded into the presses
Whole bunch pressing
- reduces chance of oxidation before and during pressing. Can add inert gases to help with this.
- very gentle form of pressing. Produces juice lower in solids, tannins and colour
- stems help break up mass of grape skins and provide channels for juice to drain
- only an option of grapes are HAND-HARVESTED
- grapes take up a lot of room in the press so fewer grapes can be loaded into each press cycle
** only suitable for small batch prem wines
Free run juice
- grapes drained off as soon as grapes are crushed
- FREE RUN JUICE
- can make wine only from this
- reduces final volume of wine so has cost implication
- juice which is LOWEST in:
- SOLIDS
- tannin
- colour
Press Juice
- juice that runs off through pressing
- has lower acidity and less sugar than FRJ (similar to free run juice but as pressing continues, more solids, tannins and colour are extracted)
- wines are fuller bodied
- Can separate into press fractions
- can be blended later in winemaking and maturation process
- later fractions likely to be too astringent or bitter (from PHENONLIC COMPOUNDS in skin, seeds or stems)
- likely to be discarded
What is hyperoxidation?
- technique of deliberately exposing the must to large quantities of oxygen before fermentation
- targets compounds in the must that oxidise most readily
- as they oxidise, compounds turn brown
What is the aim of hyperoxidation during fermentation?
- compounds precipitate
- wine returns to normal colour
- produce wine which is more stable against oxidation after fermentation
- helps remove bitter compounds from unripe grape skins, seeds and stems
What is the risk of hyperoxidation?
- can destroy some volatile aroma compounds found in must and is typically suited to neutral grapes (e.g. chardonnay)
Give an example of hyperoxidation
- reduces levels of volatile THIOLS and METHOXYPYRAZINES in Sauvignon Blanc
- would not do hyperoxidation if an aromatic fruity or herbaceous style of wine was desired
What are the costs associated with hyperoxidation?
- equipment needed isn’t expensive
- it is an extra step in winemaking process which requires labour to set up and monitor
When does clarification of the must take place?
- between PRESSING and FERMENTATION
What does clarification achieve?
- reduce amount of suspended solids in the must
Solids:
- skin
- stems
- seeds
what percentage of solids do you aim for in the must?
0.5 - 2%
Wines with higher levels of solids…
- some winemakers want higher levels so may not clarify at all
- want more texture in wine, a subtle astringency
- can get more aromas during fermentation which add complexity
EXAMPLE: suitable for prem chardonnay
- needs careful monitoring and management
- high levels can give REDUCTIVE SULFUR COMPOUNDS which will produce off-flavours
- only suitable for small prem production
Low levels of solid in the must…
- better for fruity aromas
- provides nutrient for yeast
Over-clarification can result in…
stuck fermentation
What are the four methods of clarification?
Sedimentation
Flotation
Centrifugation
Clarifying Agents
Clarification: Sedimentation
- simplest form
- AKA ‘settling’
- cheapest method as requires no extra equipment or additives
- takes most time so increased pressure on labour and time
- mainly used for small volume prem production
1) suspended solids in must fall over time with gravity
2) must is chilled to approx 4 degrees (reducing rate of oxidation and microbial spoilage, also avoids spontaneous fermentation)
3) rate depends on size and shape of vessel ( Large, tall vessels: longer process
- Smaller, short vessels: shorter process )
4) takes between 12 and 24 hours
5) clear juice transferred to fermentation vessel, leaving sediment of solids at bottle of sedimentation vessel
- aka: RACKING
- solids left behind will often be filtered by cross-flow or depth filters to extract extra juice
- used to clarify wine as well as must
Clarification: Flotation
- process of BUBBLING GAS up through the must
- as bubbles of gas rise, they bring up solid particles
- particles then skimmed off top of vessel
- speeds up rate of clarification
- inert gas used (normally nitrogen)
- fining agents must be added to must for technique to be successful as helps bind particles together
- can only be used on must and NOT wine
- little bit more expensive than sedimentation due to equipment needed but is quick and effective
- can be used in continuous or batch process
- requires:
- gases
- fining agents
- equipment for bubbling gas through the liquid
- must does not need to be chilled so save on energy costs
Clarification: Centrifugation
- machine that comprises a rapidly rotating container
- uses centrifugal force to separate solids from liquids
- used continuously (rather than as a batch process) so saves time and labour costs
- expensive to buy so only used in wineries processing large volumes of must quickly
- increase oxygen exposure to must unless machine is flushed with inert gases so has implication on costs
- can be used on wine as well as must
Clarification: Clarifying Agents
- number of different compounds can be added to the must as processing aids to speed up rate of sedimentation
- EXAMPLE: PECTOLYTIC ENZYMES break down pectins in must (can only work on must and NOT wine)
- Some fining agents can aid clarification of both must and wine
- cost in purchasing agents but may be justified against time and energy save compared to sedimentation
What are pectolytic enzymes?
- clarifying agent used in the clarification process of white wine making
- pectins naturally found in plant cell walls
- breaking down pectin allows for rapid separation between liquid juice and solids
What temperature would you ferment at if you wanted a less-fruity style of wine and might want to use some oak?
- warmer temp
- 17 to 23 degrees
- promotes yeast health
- avoid production of certain esters - ISOAMYL ACETATE
What temperature would you choose if you want to protect volatile aromas and flavour compounds?
15 degrees
Fermenting in stainless steel
- popular for fruity, floral white wines
- can control temps
EXAMPLES:
- Sauvignon Blanc
- Veneto Pinot Grigio
Fermenting in concrete/old vats
- good for fermenting at slightly warmer temps
EXAMPLES:
- Chablis
- white Rioja
Fermenting in small oak barrels
- good for some prem and super-prem chardonnay
- monitoring can be a bit labour intensive rather than just using one large vessel
- wines tend to have deeper colour and fuller body (oxidative environment; more oak-derived aromas due to yeast activity during fermentation)
- increased contact between wine and yeast lees which gives more texture
- give more blending options as wine in each barrel will be different after fermentation process
What are the effects of MLC on White Wines?
- reduction in acidity (increasing pH of wine)
- increase in microbiological stability
- modification to flavours of wine
What is the effect of MLC on low-aromatic varieties?
choice between:
- perceived greater complexity of wines that have been through MLC
- primary fruit characters of those which havent
What is the effect of MLC on aromatic varieties?
- avoided so as to preserve primary aromatics, even though they are high-acid wines
- preserve individual varieties
What adjustments can MLC make to the wine?
- can adjust acidity at this stage
- can reduce alcohol of wine at this stage
What maturation are prem and super prem wines likely to go through?
- Prem and super-prem wines made from low-aromatic varieties likely to be aged in small oak barrels to increase texture and complexity of flavour
- aromatic varieties would not
What maturation process are inexpensive wines likely to go through?
- likely to be too costly so get oak influences through other oak alternatives
What are the aims of lees ageing in white winemaking? (5)
- give body
- soften mouthfeel
- helps stabilize wine
- protect wine from oxygen
- may introduce some reductive sulfur compounds
- at low levels can be desirable (struck match, smoke)
What is batonnage?
- stirring the lees from bottom of vessel and mixing with wine
- optional
- increases release of yeast compounds in wine
- use rod and manually stir lees in wine
- increases oxygen exposure as have to remove bung from vessel
- can result in an increase in effects from dead yeast and decrease in fruity flavours
- can lead to development of reductive sulfur compounds and off-aromas so needs v careful management
What is an alternative option to batonnage?
BARREL RACKS
- can easily roll the barrels to agitate the lees
- doesn’t involve opening vessel
Cost of lees agegin
- very costly to do this on a number of vessels so only likely for prem and super-prem production
