D16: White Winemaking Flashcards
1
Q
Why would you leave grapes in contact with the skin during white wine making?
A
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
2
Q
Why would you NOT carry out skin contact during white wine making?
A
”- doesn’t suit all styles of wine
- can make wine seem coarse or bitter to taste
- most have zero or minimal skin contact
3
Q
What is the process for skin contact in white wine making?
A
- 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
4
Q
Why would a winemaker want minimal skin contact?
A
- 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
5
Q
What are the benefits of skin contact?
A
- maximises flavour extraction
- good for aromatic varieties with lots of aroma compounds to be extracted
6
Q
What varieties benefit from skin contact?
A
- Riesling
- Gewurztraminer
- Viognier
- Muscat
- Sauvignon Blanc
(helps give these wines texture as they often aren’t matured in oak)
7
Q
What are the negatives of skin contact?
A
- homogenisation
- can reduce variations between grape varieties and different vineyard sites
8
Q
How long does skin contact take?
A
- ranges from an hour to 24 hours
- greater length of time on skins leads to greater extraction of flavour and tannins
9
Q
What impact does temperature have on skin contact?
A
- 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
10
Q
What is orange wine?
A
- 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
11
Q
Grapes are almost always pressed to…
A
separate skins from juice before fermentation
12
Q
Is pressing usually gentle or firm - why?
A
typically gentle pressing to avoid extraction of unwanted compounds from skins and seeds of grape (e.g. tannins and colour)
13
Q
Destemming?
A
- important choice
- grapes normally destemmed and crushed before being loaded into the presses
14
Q
Whole bunch pressing
A
- 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
15
Q
Free run juice
A
- 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
16
Q
Press Juice
A
- 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
17
Q
What is hyperoxidation?
A
- 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
18
Q
What is the aim of hyperoxidation during fermentation?
A
- 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
19
Q
What is the risk of hyperoxidation?
A
- can destroy some volatile aroma compounds found in must and is typically suited to neutral grapes (e.g. chardonnay)
20
Q
Give an example of hyperoxidation
A
- 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
21
Q
What are the costs associated with hyperoxidation?
A
- equipment needed isn’t expensive
- it is an extra step in winemaking process which requires labour to set up and monitor
22
Q
When does clarification of the must take place?
A
- between PRESSING and FERMENTATION
23
Q
What does clarification achieve?
A
- reduce amount of suspended solids in the must
Solids:
- skin
- stems
- seeds
24
Q
what percentage of solids do you aim for in the must?
A
0.5 - 2%
25
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
26
Low levels of solid in the must...
- better for fruity aromas
| - provides nutrient for yeast
27
Over-clarification can result in...
stuck fermentation
28
What are the four methods of clarification?
Sedimentation
Flotation
Centrifugation
Clarifying Agents
29
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
30
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
31
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
32
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
33
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
34
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
35
What temperature would you choose if you want to protect volatile aromas and flavour compounds?
15 degrees
36
Fermenting in stainless steel
- popular for fruity, floral white wines
- can control temps
EXAMPLES:
- Sauvignon Blanc
- Veneto Pinot Grigio
37
Fermenting in concrete/old vats
- good for fermenting at slightly warmer temps
EXAMPLES:
- Chablis
- white Rioja
38
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
39
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
40
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
41
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
42
What adjustments can MLC make to the wine?
- can adjust acidity at this stage
| - can reduce alcohol of wine at this stage
43
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
44
What maturation process are inexpensive wines likely to go through?
- likely to be too costly so get oak influences through other oak alternatives
45
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)
46
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
47
What is an alternative option to batonnage?
BARREL RACKS
- can easily roll the barrels to agitate the lees
- doesn't involve opening vessel
48
Cost of lees agegin
- very costly to do this on a number of vessels so only likely for prem and super-prem production
