D1: Vinification Flashcards
What are the compounds that make up wine?
Water is about 85%
Alcohol
Glycerol
Acids - tartaric and malic, smaller amounts of lactic and acetic
Wine aromatics
Residual sugar
Phenolics
What compounds can add sweetness, or a sweet sensation, to a wine?
Residual sugar
Alcohol can contribute a sense of sweetness
Glycerol has a slightly sweet taste
What impact does alcohol have on the taste of wine?
Adds a sense of sweetness and bitterness.
Warms the mouth
Gives the wine body
May reduce the volatility of aromas
What is a typical wine pH?
3-4 (3 is 10 x more acidic that 4)
What is the typical unit of measure of acid in a wine and what range is normal?
Equivalent g/l of tartaric acid - normally 5.5 - 8.5 g/l
What acid is considered a fault in high concentration?
Acetic acid (vinegar)
Give 2 examples of grape derived aromatic compounds
Methoxypyrazines - grassy/green pepper in Sauvignon Blanc
Rotundone - pepper aroma in Shiraz/ Grüner Veltliner
What is 4MMP?
Aromatic compound released in fermentation that gives box tree aroma to Sauvignon Blanc
What are terpenes? Give examples
Aroma compounds formed from precursors during fermentation
From Muscat:
Linalool (floral)
Geraniol (rose like)
How are esters derived?
Esters are formed from acid and alcohol, during fermentation
What do esters contribute to a wine?
Fresh and fruity flavours in young wine - e.g. apple/ pineapple
e.g. isoamyl acetate gives aroma of bananas
What aroma compounds originate from fermentation?
Esters (fruity, sweet flavours)
Acetaldehydes (fino sherry)
Diacetyl (buttery aroma)
Sulphurous compounds (struck match to rotten eggs)
Give 2 examples of aroma compounds that are not grape or fermentation derived
Vanillin comes from oak
Eucalyptol can be absorbed into grape skins from nearby eucalyptus
Name a model for categorising wine aromas, and the key categories that make it up
Vicente Ferreira’s model for wine aromas
- compounds common to all wine
- impact aromas
- contributory aromas
- nonvolatile wine matrix
What range of residual sugar might you fine in different wines?
‘Brut nature’ sparkling - 0-1g/l
Dry wine: 2-3g/l
Port: 35-120 g/l
Sweet wine: Sauternes 150 g/l
Sweet wine: Perdo Ximenez 400 g/l
What are the EU classifications of sweetness in still wine?
Dry/sec/trocken: up to 4 g/l, or up to 9g/l if acid is not more than 2 g/l less
Medium dry/ demi-sec/ halbtrocken: 4-12 g/l, or up to 18 g/l if acid is not more than 10 g/l less
Medium sweet/ ioelleux/ lieblich: 12-45 g/l
Sweet: 45 g/l or more
Give examples of phenolic compounds
Anthocyanins
Tannins
What are common practices for making organic wine?
Depends on the certifying body. e.g. EU allows SO2 to be added, US excludes it.
Use organic raw materials where possible. e.g. organic egg white for fining
Excludes certain practices, e.g. partial dealcoholisation of wine
What are the sources of wine aromatic compounds?
- Aromas from grapes
- Aromas created from grape precursors
- Aromas created by fermentation
- Aromas from other sources
What are common practices for biodynamic winemaking?
Always made from certified biodynamically grown grapes
Other requirements can vary by county, even when certified by Demeter International.
e.g. UK producers can use organic or commercial yeast types. US can only use commercial year on a case by case basis, if fermentation is stuck
Adding many products is not permitted. e.g. isinglass
What are common practices for natural winemaking?
There is no agreed definition of a natural wine
Typically refers to the fewest possible interventions. e.g. use ambient yeast, minimal SO2.
What 2 gases are fundamental to the majority of winemaking?
Oxygen
Sulphur dioxide
What impact does the presence of oxygen have on wine?
Oxygen typically breaks down many flavours that make fresh, fruity wines. e.g. thiols in Sauvignon Blanc
Oxidation typically creates nutty/ savoury flavours, e.g. acetaldehyde
White wines become darker and browner
What compounds may help protect against the presence of oxygen in still wine?
Phenolic compounds in red wine are anti-oxidative
How are oxygen levels limited in winemaking?
Avoid ullage in vessels; fill to the top and use tight seals
Use inert gases to flush out oxygen/air from equipment before it makes contact with wine
Add sulphur dioxide, which is anti-oxidative
Use impermeable containers: stainless steel and concrete over wood; screw cap over cork
Keep temperatures lower
When is oxygen required in winemaking?
At the start of fermentation, oxygen promotes healthy yeast growth
Early exposure may increase the stability of white wine to oxygen increasing ageing potential
In red wine oxygen is required for the reactions between anthocyanins and tannins that stabilise colour
Some oxygen exposure derived compounds may give desired characteristics: dried fruits, honey, caramel, coffee, leather, mushrooms
Some fortified wine requires oxygen: Oloroso, Madeira, Tawny port
How is oxygen exposure increased during winemaking?
Cap management techniques that spray/splash wine
Smaller wooden barrels
increase rackings/ lees stirring
Increase ullage
pump oxygen through (micro-oxygenation
What properties does sulphur dioxide have in winemaking?
Anti-oxidant (indirect)
Anti-microbial
What SO2 levels are permitted by the EU?
160 mg/l in red wine
210 mg/l in white wine
Over 10 mg/l requires a label that the wine contains sulphites
How can winemakers reduce SO2 requirements?
Good hygiene and grape sorting limit microbes
Limiting oxygen exposure during winemaking
Lower temperatures during winemaking
What states does SO2 exist in wine and how can these be influenced?
Bound SO2 has reacted with compounds in the wine and has limited benefits
Free SO2 is either inactive (most) or molecular (limited proportion).
Molecular SO2 is most beneficial.
Greater proportions exist at lower pH
How are grapes and must protected in harvest and transportation?
Pack in smaller crates to protect against crushing
Keep temperatures lower - harvest at night
Add SO2 (potassium metabisulfite)
Keep equipment clean/ sanitised
What processes may a grape be exposed to before fermentation?
Chilling
Sorting, or triage
Destemming
Crushing
How can grapes be sorted?
Remove unwanted grapes/bunches before harvest
Sort by hand - on a table, a conveyer belt, or a vibrating belt (also removed MOG)
Optical sorting
What are the implications of increasing sorting?
Increasing sorting, typically increases cost, and lowers yields as more grapes are removed. It may be required in poor years, if there are larger number of unripe or mouldy grapes
Why are some grapes not de-stemmed?
It depends on the wine being made:
- Some red wine fermentations use whole bunches, which increase tannin levels from stems (stems need to be ripe)
- carbonic maceration needs whole bunches
- some white wines and sparkling wines require whole bunch pressing
Explain crushing vs. pressing
Crushing breaks the skin of grapes and releases juice to instigate fermentation. Care is taken to leave seeds whole. Can be carried out by feet.
Pressing is the separation of juice or wine from skin and seeds
What are the common types of press?
Pneumatic press uses and air sack in a tank to apply pressure to grapes. Investment is greater, but the pressure control is greater and inert gas flushing can be carried out.
Basket press (also vertical or Champagne press) is unsealed, possibly more gentle that a pneumatic press, but more labour intensive as they hold a smaller load
Horizontal screw press is similar to a basket press
Continuous presses, which are better suited to high volume, inexpensive wine
What is the name for solid remains left over pressing?
Pomace
What are the common adjustments made to must?
Enrichment (chaptalisation, concentration, RCGM addition)
Reducing alcohol (dilution)
Acidification (4 types of acid commonly added: Tartaric, malic, citric, lactic)
Deacidification (2 compounds commonly added: potassium carbonate, calcium carbonate)
What practices are covered by the term ‘enrichment’?
Chaptalisation - adding dry sugar
Concentration of sugar levels. e.g. reverse osmosis/ cryoextraction
Adding RCGM or other grape products
What level of chaptalisation is allowed in the EU?
It depends on the area:
Cooler regions may add up to 3% (to a maximum of 11.5% in white and 12% in red)
Warmer regions may add up to 1.5%, and are limited to grape concentrate or RCGM
How is alcohol reduced prior to fermentation?
Typically dilution with water, although the practice is tightly controlled. Aromas and flavours are also diluted
How and when is acidification carried out?
Tartaric acid is usually added, although citric (not in the EU), malic and lactic acids can also be added
Acidification can happen at any point, although typically before fermentation
What level of de-/acidification is allowed in the EU?
It depends on the area:
In cooler climates, deacidification of up to -1 g/l is allowed
In warmer climates, acidification of up to 2.5 g/l is allowed
Why do winemakers acidify must/wine?
In warmer climates, malic acid levels may drop dramatically during ripening
How is deacidification carried out?
Calcium carbonate or potation carbonate is added, which precipitates tartrates out of the must/wine
If deacidication is carried out prior to fermentation, the winemaker must bear in mind some further reduction in acid may take place due to MLF
What compounds are produced during fermentation?
Yeast primarily convert sugar into alcohol and carbon dioxide, in the absence of oxygen
Other compounds include:
- small amounts of volatile acid
- small amounts of SO2
- aromatics from aroma precursors (e.g. thiols like 4MMP)
- aromatics from yeast (e.g. esters that give fruity flavours)
Glycerol
What species of yeast are used by wine makers?
Saccharomyces cerevisiae is the most common due to its resistance to SO2 and alcohol levels
Saccharomyces bayanus is used for higher alcohol content, or re-fermenting sparkling wine
What yeast sources are there?
Ambient yeast - mixed yeast varieties that live on grapes and in the winery, although S. cerevisiae is dominant over 5% alcohol
Cultured yeast from a laboratory can be selected for different characteristics. e.g. enhancing aromatics, or retained fruit
List the advantages and disadvantages of ambient yeast for fermentation
Advantages:
- increased complexity of aroma compounds
- free
- unique varieties may lead to unique expressions of terroir
- marketing tool
Disadvantages:
- risk of spoilage yeasts (brettanomyces) and bacteria
- fermentation may take longer or get stuck
- variable product
List the advantages and disadvantages of cultured yeast for fermentation
Advantages:
- reliable, fast fermentation
- less danger of spoilage
- consistent product
- choice of strains to impact flavour
Disadvantages:
- cost
- potential similarity of flavours across the industry
What are typical fermentation temperature ranges for different wine styles?
Cool: 12–16°C for fresher fruitier white and rosé
Mid-range: 17–25°C for easy drinking red, or barrel fermented white
Warm: 26–32°C for powerful reds to maximise colour and tannin extraction
How is temperature controlled during fermentation?
Coolant jackets in stainless steel vats
Move ferments into warmer/cooler cellars
Pumping over (délestage) reduces heat
What are different fermentation vessels normally made from and what characters do they bring?
Stainless steel - neutral, good temperature control, good for mechanisation
Concrete - efficient temperature control. Can be cheap, or expensive. Lined with resin
Wood - need good hygiene. Retains heat. May oxygenate more. Less common for reds due to poor cap management
What is MLF and how does it arise?
Malolactic Fermentation, or conversion, is from lactic acid bacteria converting malic acid to lactic acid
Needs a temperature >15°C, a low pH and low-moderate SO2
Which wines typically go through MLF?
All red wine, in combination with normal fermentation, because of the higher temperatures of fermentation
Acidic white wines in non-aromatic grape varieties, e.g. Chardonnay
What characteristics does MLF bring to a wine?
Reduction in acidity
Some red colour loss
Greater microbial stability
Potential reduction of fruit character and addition of buttery flavour
What techniques can reduce alcohol post-fermentation?
Reverse osmosis to remove a mixture of water and alcohol - distillation can remove alcohol from this mix before adding it back
Equipment called a spinning cone
How can colour be adjusted?
Fining may reduce unwanted colour
Some colours may be added, e.g. grape derived MegaPurple
What are the main choices when storing wine before bottling?
Fruity, fresh wines that have limited oxygen exposure are likely to be held in stainless steel and bottled quickly after fermentation
Wine may be matured in bulk in large inert vessels, or barrels that allow slow oxygen exchange
Barrels may be old or new wood
Wine may be help on its lees, and stirred or left.
How does the role of oxygen impact the maturation of white wine differently to red wine?
Red wine has anti-oxidative properties from phenolic compounds. Therefore it can typically withstand a longer maturation of 12-24 months, compared with 6-12 for whites
How does the size of a barrel impact maturation?
Water and alcohol impregnate the wood and slowly diffuse out of the barrel sides, to be replaced by ullage. The ullage increases oxidation.
As smaller barrels have a larger surface area to volume ratio, this process is faster compared with larger barrels
What is micro-oxygenation and what are its benefits/risks?
Micro-oxygenation is bubbling oxygen through wine, measured in mg/l per month
It is much more precise than barrel ageing, and saves money over making barrels.
It is an unproven technique however which has risk as longer term outcomes are unknown, and may provide a great chance of spoilage.
Why is wine matured in cellars?
Cellars are cool, which slows down the effect of oxygenation, and prevents some undesirable reactions that can happen at warmer temperatures.
It also reduces evaporation loss
How does an oak barrel’s impact on wine change over time?
Oak has extractable compounds, mainly tannins and aroma compounds.
The levels of these in oak typically halve in year 1, and by year 4 will not contribute noticeably.
Permeability to oxygen and evaporation remain unchanged over time.
What are common barrel sizes for maturation?
Barriques 225l
Foudres - large vessel +2,000l
What types of oak are there and what are their key characteristics for wine maturation?
European - higher in tannin
American - high in lactone (coconut)
Hungarian - tight grain, slow release of compounds
Russian
Slavonian
How does oak type impact cost?
Manufacturing American barrels is about half the cost of European as wood can be sawn, not split.
What are the key processes in making a new barrel?
Season the wood for 2-3 years
Saw/split into staves.
Heat to bend (toasting)
What alternatives are there to barrel ageing to achieve oak aromas?
Adding oak chips or staves in a stainless steel or concrete vessel
What forms lees?
Dead/dying autolysed yeast
Bacteria
Grape fragments
Precipitated tannins
What is different types of lees settle over time?
Gross lees settles in the first 24 hours after fermentation.
Fine lees is everything after that.
What impact does lees have on wine?
Autolysed yeast release compounds that:
- contribute flavour
- bind with phenolic compounds to reduce colour and soften tannins, or astringency of wood compounds
- stabilise the wine against haze causing proteins
- protect from oxygen
- produce sulfur compounds (potentially good in low quantity and bad in high)
Describe racking
Racking is the transfer of wine between vessels to remove sediment.
It can be oxidative, unless inert gas flushing is used.
It can be carried out multiple times, depending on the desired oxygen exposure and lees exposure
List potential blending options
- grape variety
- different locations
- different growers
- different vintages
- different treatment in the winery (free juice vs press; concrete vs wood; etc)
- just different taste
How can laws impact blending?
PDO wines have to be made 100% of grapes from the designate area.
Some regions must be 100% specific varieties, e.g. Sangiovese in Brunello di Montalcino
Why is wine blended?
Balance characteristics
Achieve consistency
Achieving a desired style
Enhance complexity/depth
Minimise faults
Reach viable volumes
Balance cost - e.g. Semillon is cheaper than Chardonnay
Why might blending be avoided?
‘Single vineyard’ might be good for marketing
May dilute distinct characteristics or aromas
What steps are involved in finishing a wine ahead of packaging?
All optional/ as required
8 weeks ahead or more: blend, analyse and adjust
4-6 weeks: Check protein and tartrate stability for further fining
1-2 weeks: Add any sweetening
0-1 days: adjust SO2 and oxygen
During bottling: quality sample
What techniques clarify wine?
Sedimentation
Centrifugation
Fining
Filtration
How is sedimentation carried out?
Leave the wine to settle and rack off.
It is a slow process suitable for premium/ super premium wines
How is centrifugation carried out?
Spin the wine at high speed in a centrifuge. The capital investment is high, so it is normally used in high-volume wineries
What types of fining agent are there?
Ones that remove:
- unstable protein: e.g. Bentonite
- phenolics with undesirable colour/bitterness: e.g.: egg albumin; gelatine, casein; isinglass; vegetable protein; PVPP
- colour and off-odours: charcoal
How is fining carried out?
Small sample testing helps determine the desired quantity of fining agent.
Agents have the opposite charge to the colloid, bind to it, and form a larger particle that settles faster.
List fining agents that remove phenolics, the agent properties and typical target wines
Egg albumin: removes harsh tannins. It is an allergen
Gelatin: protein collagen from pork removes bitterness in red wine and browning in white wine
Casein: milk protein that removes browning from white wine
Isinglass: protein collagen from fish bladders that clarifies white wines
Vegetable proteins: suitable for vegan friendly wine
PVPP (Polyvinylpolypyrrolidon): insoluble plastic powder removes browning and astringency from oxidised white wine
What are the main types of filtration?
Depth filtration:
- diatomaceous earth (pure silica)
- sheet filter (plate and frame, or pad filter)
Surface filtration
- membrane filter (normally very fine, sterile filtering, that requires pre-filter so that membranes are not blocked)
- cross-flow filter (very fine, and high volume, but expensive capital investment)
What different types of compound stability does winemaking normally refer to?
Protein stability - fining with bentonite is key
Tartrate stability
Microbial stability - sterile filtering is most common
What are a winemaker’s options to increase tartrate stability?
Cold stabilisation: hold wine at -4 °C for 8 days before filtering
Contact process: add potassium bitartrate, cool to 0°C for 1-2 hours and filter
Electrodialysis: charged membrane removes certain ions. High investment, but low running costs as no chilling is required
Carboxymethylcellulose (CMC): extracted from wood, used in white/rosé wine. Much cheaper than chilling
Metatartartic acid: Used in red wine in place of CMC, but time limited
What are target SO2 levels?
Molecular SO2 changes with pH so there is a range: at a lower pH less SO2 is needed
- white wine: 25–45 mg/l (lower than for - red wines due to lower pH)
- red wine: 30–55 mg/l
- sweet wine: 30–60 mg/l
How can dissolved oxygen levels be reduced?
Sparging with inert gas
List common types of wine fault
Cloudiness
Tartrate formation
Re-fermentation
Cork taint
Oxidation
Volatile acidity
Reduction
Light strike
Brettanomyces
How is cork taint identified?
Wet cardboard/ wet leaves smell
What identifies oxidation as a fault in wine?
Prematurely brown in colour, loss of primary fruit and vinegary smell
What causes excessive volatile acidity and how is it identified?
Acetic acid bacteria may arise if levels of SO2 are too low. These bacteria produce acetone/vinegar smell
What causes reduction and at what stages in winemaking does it typically occur?
Reductive compounds are formed either under yeast stress in fermentation (normally low nitrogen), or exhaustion of oxygen in closed vessels in lees ageing.
How can reduction be avoided?
Ensure yeast has sufficient nutrients and oxygen
Lower SO2 levels (especially with impermeable closures)
What is light strike and how is it avoided?
Predominantly UV light causes the production of volatile sulphur compounds.
It can be avoided by using dark glass, and storing wine out of daylight and fluorescent displays.
What is ‘brett’?
Brettanomyces is a yeast that creates animal or farmyard smells
It is considered a fault in high quantity. In low quantity it may add complexity to a wine.
How is ‘brett’ avoided?
The cells can survive in wood in old and new barrels
It can hopefully be avoided through:
- excellent hygiene
- maintain SO2
- keep pH low
- keep fermentation and MLF as close together as possible so that SO2 can be added as soon as possible
Once packaged, what sources of oxygen can impact a wine?
Dissolved oxygen
Headspace
Contained in the cork/closure
Oxygen transmitted through the cork
What are the advantages and disadvantages of packaging in glass?
Advantages:
- inert
- easy to sterilise
- inexpensive
- recyclable
- impermeable
Disadvantages:
- high carbon footprint (manufacture and weight to transport)
- fragile
- rigid (headspace)
- risk of light strike
What are the most common alternatives to glass packaging?
Plastic - cheap, light, but not suitable for long term
Bag-in-box/ pouch - easy storage, lightweight, no headspace, but not suitable for long term
Brick/Tetra Pak - easy storage, light - costly equipment to set up
Can - light weight, robust, impermeable, needs to be lined with plastic
What are the most common closures for glass bottles?
Natural cork
Technical cork
Synthetic cork
Screwcap
Glass stopper (Vinolok)
What are the risks and benefits of using natural cork?
Renewable
Good oxygen barrier
Universally liked by consumers
Can taint through TCA production unless rigorous quality controlled (e.g. gas chromatography) or steam cleaned
What compound is associated with cork taint?
TCA: 2,4,6-trichloroanisole
What is a technical cork?
Agglomerated cork granules, held together with glue.
Normally short term use only. Different oxygen ingress rates can be selected for longer ageing.
What are the advantages / disadvantages of screwcaps?
Very tight closure
Easy to open
No taint risk
Wide degrees of acceptance
May require lower SO2 to avoid reduction
What are considered ideal storage conditions for maturing packaged wine?
Undisturbed
Cool, dark place
Constant temperature, ideally around 10–15°C
Constant humidity, stored on side if cork
What three categories do hygiene procedures fall into?
Cleaning - surface dirt
Sanitation - removing organisms to very low levels with detergent/ steam/ etc
Sterlisation
What is HACCP?
Hazard Analysis of Critical Control Points (HACCP) is an approach to documenting and managing all hazards that could impact the wine, e.g. glass fragments in a bottle.
It requires investment of time and cost.
What is an ISO certification?
International Organization for Standardization (ISO) can audit and certify that quality standards are being met (ISO 9000 and 9001).
It is carried out for a fee and may be required by large retailers to be a supplier.
How and why is a wine made traceable?
Lot numbers are given to wine (EU requirement), which the winemaker can use to trace back and confirm the ingredients and processes used to manufacture the individual lot.
When and why was the switch made from shipping barrels to bottles in Bordeaux?
In the 1920s, shipping bottles reduced the possibility of blending or adulteration of the finished wine.
When, why and how is wine shipped in bulk over bottle?
30% to 40% of wine is shipped in bulk, typically lower value, high volume wine.
Shipping costs are substantially reduced as large polyethylene bags can be used in a shipping container, instead of hundreds of glass bottles.
High quality bottling plants can bottle the wine near to the final market.
What are the benefits / limitations to shipping wine in bulk containers?
Lower costs and carbon footprint
Great temperature stability
Tighter quality control on filling/emptying, and potential further adjustment
Potentially extend shelf life
Only viable for larger producers (min 3 containers per year)
How does machine harvesting compare with hand harvesting, in the process of must production for white wine?
Machines harvest berries only, whereas hand harvesting takes whole bunches.
Therefore hand harvesting must decide whether to de-stem before crushing and/or pressing
What are the key decisions to be made in white wine production?
- Harvest method
- Sorting level
- De-stem (hand harvest only)
- Crush method/extent
- skin contact time
- press method/ pressure
- hyperoxidation
- must adjustments
- clarification level/method
- fermentation
- post-fermentation adjustments
- MLF
What white varieties are most likely to have skin contact?
Aromatic varieties: Reisling, Gewurtztraminer, Viognier, etc
What impact does skin contact have on white wine?
Potential enhancement of aroma and flavour compounds
Can lead to bitter/ coarse wine
How long are white grapes left with skin contact? Anything else specific about the process?
Skin contact is typically 1-24 hours
Juice is typically chilled to below 15°C
What is orange wine and how is it made?
Orange wine is made from white grapes and normally fermented on skins, resulting in a larger component of oxidised compounds from the skins.
Orange wines are usually dry, tannic, with tertiary flavours such as nuts and dried fruit.
What winemaking options are available for white grapes up to and including pressing?
Hand picked grapes can be destemmed and/ or crushed before pressing.
Whole bunch pressing can be used for premium wines
Inert gases can limit oxygen exposure during these phases
Free run juice is from crushed grapes, or an initial pressing.
More pressure will result in press juice with increased solids, tannin and colour.
What is hyperoxidation and when is it used?
Hyperoxidation is deliberately exposing must to large quantities of oxygen before fermentation.
It is used to produce a wine that is potentially more stable, and removes some bitter compounds.
It can destroy some aroma compounds and so is better with neutral grape varieties, e.g. Chardonnay
Why and how is white grape must clarified?
Clarification of must is optional prior to fermentation. It reduces the risk of spoilage from solids and their reactions
Overall the range of aromas may be reduced by clarification. However it thought to obtain better fruity aromas
It is usually carried out by one of:
- 12-24 hours of sedimentation
- flotation of solid matter from bubbling inert gas through must, with a fining agent, to skim off
- centrifuge
- pectolytic enzymes
When is white wine fermented in oak?
Small oak barrels are typically used for premium/ super-premium, non-aromatic grapes, particularly Chardonnay
What temperatures are used for white wine fermentation?
12°C - 16°C for fresh fruity wine.
This many be increased to 17°C -25°C for more savoury flavours
What white wines are matured in wood?
Neutral, non-aromatic varieties may be matured in wood, particularly premium/ super-premium wines
What winemaking processes or decision points are there when maturing and finishing white wine for sale?
- blending
- use of oak
- lees ageing
- further blending
- stabilisation
- clarification
- packaging
What is the potential impact of lees ageing on white wine?
- increased body/depth
- soften mouthfeel
- stabilise
- protect from oxygen
- introduce some reductive sulphur compounds
What is the french word for lees stirring?
Bâtonnage
Set out the process of lees stirring
Lees stirring is optional.
Traditionally a bung is removed and lees are stirred by hand with a rod. This increases oxygen exposure and reduces the chance of reductive compounds.
Lees can be stirred without removing the bung (e.g. rotate barrel).
What methods are there for concentrating grape must to produce wine with residual sugar?
- drying grapes on the vine
- drying grapes off the vine
- noble rot
- freezing grapes on the vine
How are grapes dried on the vine? Give examples
Stage 4 of ripening (extra-ripening) results in water loss by transpiration. This results in extra-ripe flavours.
Long dry summers are required to avoid grey rot.
e.g. Pinot Gris may develop tropical fruit and dried stone fruit flavours.
The stem may be broken to increase water loss. This is used in Jurançon in south west France.
How are wines made from grapes dried on the vine labelled?
Late harvest
Vendanges Tardives from Alsace
Spätlese from Germany or Austria.
How are grapes dried off the vine?
Grapes can be dried over days, up to months.
Warm counties may lay grapes out in the sun - southern Italy or Spain
They can also be dried in temperature and humidity controlled room.
Recioto di Valpolicella and Vin Santo in Italy are both examples of wine made this way
How are grapes concentrated through noble rot?
Botrytis cinerea (grey rot). This must develop in a ripe grape, with damp mornings and dry/sunny afternoons.
The fungus leaves small holes in the skin that water evaporates through.
What types of wine are made from noble rot?
Sauternes
Beerenauslese
Trockenbeerenauslese
Tokaji
What is the impact of noble rot on sweet wine making?
As the rot is rarely uniform, several hand pickings are usually required.
Ideal weather conditions are unreliable and so the same vineyard may not produce botrytis every year
High doses of SO2 are required to minimise the impact of the fungal enzyme laccase. Chilling and flushing with inert gases also help limit oxidation
Thick must is harder to press, clarify and ferment
How is ice wine produced?
Healthy grapes are left on the vine until frozen in winter and harvested whilst frozen (-8°C in Canada)
Pressing frozen grapes leaves ice crystals behind and the juice is more concentrated
Grapes will often go through several freeze/thaw cycles before harvest
Stainless steel is often used to retain aromas and flavours
Oak maturation is sometimes used
What are the protected terms for ice wine?
Eiswein in Germany and Austria
Icewine in Canada
What attributes are required for ice wine varietals? Give examples
Grapes need to be hardy and thick skinned. Riesling and Vidal are common
What alternatives are there to traditional ice wine making?
Cryoextraction can replicate the effect of grapes freezing on the vine and is much cheaper, with lower risk of crop damage
How is sweet wine made by stopping fermentation early? give an example
Stopping fermentation early is more common with off-dry to medium sweet wines
The most common methods are chilling to 10°C, or a high dose of SO2. The wine is then racked and filtered
Used for inexpensive/ mid-priced wine. e.g. Moscato d’Asti
Fortified wine may use alcohol spirit to stop fermentation
How is sweet wine made by blending?
Blending in a sweetening component to dry wine reduces susceptibility to spoilage
There is a high degree of control
Suitable for inexpensive wines
RCGM or unfermented grape juice are most commonly added
What compounds are sought in red wine over white, and what methods are used to obtain them over white winemaking?
Anthocyanins, tannins and skin aroma compounds
These are extracted through:
- higher temperatures
- longer time on skins
- cap management
- matching extraction to the appropriate time (anthocyanins pre-fermentation, tannins during/after)
What promotes colour stability?
Anthocyanins are the source of colour in young red wine.
These are more stable when bonded to tannins, normally through oxygenation
At what points in red wine production can rosé be produced?
Key is to press before fermentation, as lots of colour comes out during fermentation
Two choices:
- Press after sorting
- Press after pre-fermentation maceration
What options exist in red wine making processes, that are rarely or never used in white wine?
Fermentation on skins
Mixing whole berries, or bunches, with crushed fruit for fermentation
Carbonic maceration
Semi carbonic maceration
Cap management
What maceration options are there in red winemaking and how do they differ?
Maceration before fermentation to extract colour and flavour without tannin:
- cold soaking
- using heat
Maceration during fermentation also extracts tannins
Set out options and methods for maceration before fermentation
Cold soaking: juice and skins are held at 4°C - 10°C for 3-7 days. May use cap management during this. Used with Pinot Noir maximise low levels of anthocyanins
Thermovinification: heating to around 50°C - 60°C for minutes to hours
Flash détente: destemmed and heated to 85°C and 90°C for a few minutes, under vacuum.
What is the impact of pressing red wine before fermentation?
The wine is typically inexpensive, low tannin, fruity style. It may have colour instability and should be drunk young
What options reduce the impact of grey rot (botrytis) on still red wine?
Pre-fermentation maceration with heat can denature oxidative enzymes (laccase) in the fungus
What causes a cap and how is it managed?
Carbon dioxide bubbles cause the skins to float, forming a layer separated from the rest of the fermentation. To maximise colour extraction, these can be circulated back into the wine by:
Punching down
Pumping over
Rack and return
Ganimede tanks
Rotary fermenters
How is punching down carried out?
A hand or mechanical plunger submerges the cap. This requires a small, open top vessel
What is punching down also known as?
Pigeage
How is pumping over carried out?
About 1/3 to 1/2 of the liquid in a fermentation vessel is pumped and sprayed over the top of the cap.
In an open tank this increases oxygen levels and reduces the risk of reductive flavours
How is pumping over also known
Remontage
How is rack and return carried out?
The liquid from the fermentation vessel is pumped into an empty vessel.
This is then pumped back over the cap.
It is a highly effective extractive technique, so used only 1-3 times during fermentation
How is rack and return also known?
Delestage
How does a Ganimede tank work?
Ganimede tanks bubble up CO2 (or oxygen/air) through the wine. The cap bursts when the pressure is high enough
This is highly effective and less labour intensive than rack and return, although specialised tanks are required
How do rotary fermenters function?
The closed, horizontal stainless steel tanks rotate and internal blades break up the cap
These are very effective, but imprecise, so used for larger volume mid-range reds
What is co-fermentation?
Co-fermentation is the process of fermenting different grape varieties together.
Most frequently up to 5% white grapes in a red wine fermentation. e.g. Syrah/Viognier in Côte-Rôtie
What viniculture considerations are there for whole bunch fermentation?
Grapes need to be hand harvested
Stems must be ripe
What options are there for whole bunch fermentation and how do they differ?
Carbonic maceration blankets whole bunches with added CO2. Grapes are pressed when alcohol reaches 2%
Semi-carbonic maceration - CO2 is generated by ambient yeast from crushed grapes at the bottom of the vessel. This can be continued to develop to full fermentation
Whole berries with crushed fruit - being submerged limits oxygen, and these undergo intracellular fermentation and are integrated and crushed during cap management
What chemical changes occur to grapes during whole bunch fermentation?
The oxygen free environment in whole fruit causes the cells in the grape to change to switch to anaerobic respiration. Malic acid and sugars are converted to alcohol, reducing acidity, increasing glycerol
What temperature range may be used for red wine fermentation?
20°C for fruity, low tanning
30°C for concentration and tannin for ageing
What vessels are used for red wine fermentation?
Open top would be needed for punching down, but closed top can be used
Where oak is used, it is normally large vats, but it is an option to ferment in barriques, with a small opening. This is labour intensive and used for premium/ super-premium wines only
What are the consideration for post-fermentation maceration?
Post-fermentation maceration may be from a few days to a few weeks. This is thought to extract more tannins and also encourage polymerisation, increasing ageing potential.
Because of the ageing requirement, and tank space, it is used in premium/ super-premium wines
What are the options when pressing red wine?
Pressing may be carried out:
- before the end of fermentation, with a view to finish fermenting in barrel
- at the end of fermentation, or
- after post-fermentation maceration
Wines that undergo carbonic maceration may be pressed as soon as alcohol reaches 2%, to retain low tannin.
What are the main options with MLF in red winemaking?
Malolactic fermentation can be encouraged:
- during fermentation
- after fermentation in tank
- after fermentation in barrel
What winemaking processes or decisions can be made when maturing and finishing red wine for sale?
- blending
- use of oak
- lees ageing
- further blending
- stabilisation
- clarification
- packaging
What lees ageing can be used in red wine production?
Lees ageing is not common in red wine production as it reduces colour intensity
Where it is used, it is normally fine lees, with no stirring.
What are the three main methods of making rosé wine?
“Direct pressing” before maceration. The higher the pressure, the greater the level of anthocyanins/ tannins extracted from skin
“Short maceration”, which allows for greater extraction of skin compounds.
Sometimes short maceration rosé is from the by-product of must concentration.
“Blending” mixes fermented red and white wines. This method is not allowed in most EU geographical indicators (except Champagne)
What styles of rosé are produced by different techniques?
Light coloured rosés are produced by direct pressing as maceration is minimal. Also called ‘vin gris’ wine. e.g. Provence wine
Typically deeper in colour wines are produced by short maceration. e.g. Spanish rosé and Tavel.
Blending can produce a wide range of styles
What viticulture considerations are there for grapes used in rosé?
Higher quality rosé is typically made in cool to moderate sites/ climates. Yields can be higher than reds, to produce grapes with less concentration and more acid
Harvest is normally earlier than for red wine making, although care must be taken with unripe stems
What winemaking decisions are usually made for rosé?
Rosé is normally fermented as low temperatures (12°C - 16°C) to retain aroma compounds
Oak use is light, and the wine needs sufficient fruit concentration not to be overpowered
Cultured yeast is normally used that promotes fruit flavours
MLF is normally avoided
