D1.C13. General Winemaking Options Flashcards
Name two gases that play fundamental role in winemaking and maturation
- Oxygen
- Sulphur dioxide
What are the parameters which determine whether oxygen will have a positive or a negative effect during winemaking?
Timing and the amount of oxygen exposure
What are the adverse effects of oxygen on fresh, fruity wines?
- Aroma compounds (like thiols in Sauvignon Blanc) breakdown leading to loss of fruitiness
- Products of oxidation reactions may contribute unwanted aromas to the wine like acetaldehyde
- The colour of white wines can also turn darker, becoming gold and then brown
Why are the red wines more resistant to oxidation?
Because, phenolic compounds in red wines have an anti-oxidative effect
The practice of minimising oxygen exposure during the winemaking process is sometimes called..
Reductive or protective winemaking
How can the effect of oxygen on must and wine be limited in the winery?
- Avoiding ullage in vessels by topping up
- Using inert gases like CO2, N or Argon
+ Flushing vessels, pipes and machinary
+ To fill the empty headspace - Adding SO2
- Using impermeable containers: Stainless steel and thick concrete vessels, glass bottles with screwcaps
- Keeping cool constant temperatures
What are the positive effects of oxygen for the wine?
- It is required at the start of fermentation
- Lack of enough oxygen in winemaking or storage can lead to reductive off-flavours
- In the production of some white wines, exposing the must to oxygen before fermentation is thought to lead to greater oxidation stability in the wine, and to result in increased ageing potential
- In red wines, oxygen is essential in the reaction between anthocyanins and tannins that leads to greater colour stability
- Exposure to oxygen over time also leads to changes in the aromas/flavours of wine which gives a greater range and diversity of characteristics: fresh fruits become dried fruits and notes such as honey, caramel, coffee, leather and mushroom
How can the oxygen exposure be increased during wine making?
- Use of cap management techniques
- Use of small wooden barrels that can only contain a small volume of wine
- Increasing the number of rackings or amount of lees stirring during ageing
- Allowing ullage in wine containers
- Use of techniques that involve pumping oxygen through the must
Name two factors that favors the development of Brettanomcyes?
- Oxygen exposure
- Residual sugar
What are the major effects of sulfur dioxide?
- Anti-oxidant
- Anti-microbial
- Anti enzymatic (inhibits tyrosinase and laccase)
- Wine refreshment: By binding acetaldehyde
In which form can sulfur dioxide be applied during winemaking process?
- Solid:
+ Matches, tablets (SO2)
+ Powder: Potassium metabisulfite: Dusted on fresh harvested grapes. Release 50% of its weight as SO2) - Liquid: SO2 liquifies under -15°C and 3 bars of pressure)
What is the amount of SO2 produced during fermentation?
Less than 10 mg/L
What are the maximum amount SO2 allowed for red and white wines in the EU?
- Red wines: 160 mg/L
- White wines: 210 mg/L
How are the maximum amount of SO2 allowed in sweet wines when compared with dry wines?
It is higher
After which level of SO2 in wine, it must be stated in the label? Why?
- 10 mg/L
- The concentrations of SO2 found in wine are far below toxic levels; however, even at these levels some people can have some allergic reactions
In which forms, can SO2 be found in must or wine
- Bound SO2: Inactive against oxidation and microbes
- Free:
+ Inactive form (majority)
+ Molecular: Most effective
What is the relation of pH with the levels of SO2?
A greater proportion of free SO2 is in molecular form at lower pH levels
What are the factors that determine the influences and the effectiveness of the added SO2?
- Timing
- Size
What are the critical steps in winemaking, where adding a larger amount of SO2 is more effective than adding smaller amounts throughout the entire winemaking process?
- Crushing
- End of malolactic conversion
- Bottling
Why do the quality-conscious winemakers aim to limit the use of SO2, other than legal restrictions?
High levels of SO2 can dull wine aromas/flavours and sometimes can cause the wine to taste harsh
What are the practices that can reduce the amount of SO2 needed?
- Good winery hygiene
- Effective grape sorting
- Limiting oxygen exposure
- Keeping the grapes, must and wine in cool conditions
During transportation to winery, grapes are vulnerable to:
- Oxidation
- Ambient yeasts
- Acetic acid bacteria
What measures can be taken to minimise the threats of oxidation and microbial infection?
- Harvesting and transporting the grapes at night
- Addition of SO2
- Keeping the grapes in cold storage rooms in the winery
- Sanitising the harvesting equipment/bins
- Collecting and transporting the grapes in small crates to minimise crushing
What are the transportation options for hand-harvested and machine-harvested grapes
- Hand harvested
+ To transport the grapes in small crates: Minimal crushing
+ The small crates are tipped into larger hoppers (large bins) for transport to the winery: More crushing - Machine-harvested: The fruit has already been destemmed and and is typically transported in large containers, with some release of juice
On arrival to winery, a number of options are possible and will depend on:
- Volume of the grapes
- Whether they have been hand- or machine-harvested
- Health and the quality of the grapes
How can large volume of grapes be moved on reception?
- Conveyor belt (gentler with higher quality potential)
- Screw conveyor
How can smaller volume of grapes be moved on reception?
Hand-harvested grapes can be moved around manually, often with a pallet truck or forklift
When does the winemaker choose to chill grapes on reception?
If the grapes are warm when they reach the winery
What are the advantages of chilling the grapes on reception?
- Help to preserve fruity aromas
- Reduce the threat from spoilage organisms
- Also advantageous to store the grapes if all the sorting tables, presses and other equipment is already in use
What are the options for chilling?
- Refrigeration unit: Used for whole bunches. Slower
- Heat exchanger: When the grapes are in a more fluid format (e.g. fruit that has been machine picked, grapes that are destemmed and possibly crushed). Faster
What is the disadvantage of chilling the grapes?
Higher cost due to equipment and energy cost
How can a grape grower decrease the need of chilling?
By harvesting at night or early in the morning
What is the French word for sorting?
Triage
The level of grape sorting depends on which factors?
- Ripeness and health of the fruit
- Intended final wine quality and price
- Whether any sorting has been carried out in the vineyard
- Physical state of the grapes (depending on the choices of transportation to winery)
What are the factors that increase the cost as grape sorting levels increase?
- More labour and time
- Less yield
How can grape sorting change in bad and good vintages?
- In poor years and in cool climates a greater of level of sorting may simply be required
- In very good years, fruit may arrive near perfect condition and require little sorting. MOG may still need to be removed
What is the usual sorting strategy for inexpensive wines?
No sorting
What are the key determinants of sorting?
- The health of the grapes on arrival at the winery
- The quality of the wine to be made in relation to the price that can be gained for the wine
What are the sorting options for quality wines?
- Removing unwanted grapes/bunches before picking or during hand-harvesting
- Sorting by hand on a table or a moving or vibrating belt (the latter also removes MOG) before or after destemming or both
- Optical sorting: Can be done either in a harvesting machine or at reception in the winery
Optical sorting is used for kinds of wines on price basis? Why?
- Only in premium or super-premium wines
- Due to the cost of the machine and high level of selection
In which conditions, the grapes are not destemmed?
- Red wine fermentations that use some whole bunches
- Carbonic maceration
- Whole bunch pressing for some white wines (e.g. common for high-quality sparkling wine)
What happens when the stems are not ripe in whole bunch fermentation?
They can convey unwanted green flavours and bitter tannins to the wine
What is crushing?
Application of sufficient pressure to the grapes to break the skins and release the juice, making it available for fermentation
What happens if the pressure applied for crushing is not gentle enough?
The seeds are crushed which would add bitterness
What is the traditional way of crushing the grapes?
Human feet
What does the term “must” refer to?
The substance that is being fermented. (The mixture of grape juice, pulp, skins and seeds that comes from the crusher but for white wines, must may also refer to the grape juice that is fermented)
Why soft pressing is important for both white and red wines?
- White: Not to extract tannins and avoid excessive amount of solids
- Red: To avoid extraction of excessive tannins and bitterness from skin and seeds
Name the types of presses that can be used in winemaking
- Pneumatic press (air-bag press)
- Basket press (Vertical, Champagne)
- Horizontal screw press
- Continuous press
Which of the presses that can be used in winemaking is most popular?
Pneumatic press