Level 4 D1 Chap 13 - General Winemaking Options Flashcards
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 for processing and with bottles: 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 stabilises 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
Increased rackings / lees stirring
Allow ullage in containers
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?
150 mg/l in red wine
200 mg/l in white wine
Over 10 mg/l requires a label that the wine contains sulphites
How can winemakers reduce SO2 requirements?
- Limiting oxygen exposure during winemaking
- Lower temperatures during winemaking
- Good hygiene and grape sorting limit microbes
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 Pressing
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 moldy 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
- reverse osmosis
- vacuum extraction
- chilling
Adding RCGM or other grape products
What level of chaptalisation is allowed in the EU?
1.5% to 3%
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?
-1 g/L to 2.5g/L
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
With too little acid, wine may lack freshness.
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
- unique varieties may lead to unique expressions of terroir
- free
- marketing tool
Disadvantages:
- risk of spoilage yeasts (brettanomyces) and bacteria
- fermentation may take longer or get stuck
- variable product / consistency is nearly impossible
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?
To get fermentation started, ideal temp is 25°C
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 loss red colour
- Greater microbial stability because MLF will now NOT happen in the bottle
- Potential reduction of fruit character and addition of buttery notes (notably in white wine)
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
