D1 General winemaking options Flashcards
The effect of oxygen
Oxygen is responsible for the oxidation reactions, can be positive or negative.
Negative effect on fresh, fruity white wines:
- lose aroma compounds (such as thiols)
- contribute to unwanted aroma (acetaldehyde, nutty and apple aroma)
- Change colour to darker brown
Oxygen can be limited by:
- Avoiding ullage
- Using inert gases (nitrogen, carbon dioxide, argon)
- Addition of soulful dioxide (anti-oxidative)
- Use impermeable containers (stainless steel, concrete, screw cap)
- Cool temperatures (slows down oxidation)
Positive effects:
- promote yeast growth at the start of fermentation
- protect from reductive off-flavours
- in white wine, greater oxidation stability
(by exposing the must to oxygen before fermentation)
- in red wine, is essential for greater colour stability (reaction of phenolics - anthocyanin and tannins)
- Changes aromas/flavour from fresh to dried fruit and add notes such as honey, caramel, coffee, leather, mushroom.
Oxygen can be increase by:
- Allowing ullage
- No use of inert gases
- pumping oxygen through the must
- Use of cap management
- Use of small wooden barrels
- Increasing the number of racking or lees stirring.
Red wines are less vulnerable because they contain more phenolic that have antioxidant properties.
Sulfur Dioxide
Sulfur dioxide act as an anti-oxidant and anti-microbial.
Can be applied as gas, liquid or solid, as sulfur dioxide, potassium bisulfites or potassium metabisulfite.
A small amount is naturally produced during fermentation (10 mg/L).
“Contain sulfites” if over 10 mg/L.
Maximum permitted in EU is 150 mg/L for red and 200 mg/L in white. USA organic does not allow.
The higher pH level is, the greater amount of SO2 is needed.
The timing influence the effectiveness.
Usually is added when the grapes are picked and crushed, at the end of malolactic conversion and at bottling.
High level can dull wine aromas/flavour and may cause the wine to taste harsh.
The use of SO2 can be limited by:
- Limiting the amount of harmful microbes (with good winery hygiene)
- Limiting oxygen exposure
Transportation to the winery
Once harvested and transported, the grapes are vulnerable to oxidation, ambient yeast and acetic acid bacteria (turn alcohol in acetic acid - vinegar)
To minimise oxidation and microbial infection:
- harvesting and transporting grapes at night or at sunrise (lower temperature)
- Addition of SO2 (powder)
- Using cold storage
- Sanitising equipment
- Using small crates to minimise crushing
Machine harvesters already destemmed and is transported in large crates.
Nowadays, harvesters may sort, crush and add SO2 before transporting the juice to the winery.
Chilling
If the grapes are warm, they may get chilled to a lower temperatures, preventing oxidation and therefore preserve fruity aroma, also reducing spoilage organisms.
Refrigerators can be costly in terms of equipment and energy, but can be a useful place to store grapes.
Harvesting in the night or early morning can avoid this costs.
Sorting
Sorting depends on the intended final wine quality and price.
Varies from none to very meticulous.
MOT and mouldy, under-ripe grapes can be removed.
The more sorting is done, the higher the cost (due to the labour and time needed, also because results in less yields).
For quality wines, there is a range of sorting options:
- Removing unwanted grapes during hand-harvesting
- Sorting by hand (also removing MOG)
- Optical sorting, high tech software technology to scan individual grapes.
Destemming
Hand-harvested grapes are destemmed at the winery.
Machine-harvested grapes are already destemmed.
Destemmers work by a series of blades within a rotating drum that remove the grapes from the stem.
Stems contain tannins, therefore are not always desirable.
Usually stems are kept for whole bunch pressing, whole bunch fermentation, carbonic maceration.
Crushing
The grapes are gently crushed to break the skins, release the juice without crushing the seeds.
Once crushed the grapes and the juice are left to macerate for a period that can vary from 5 days to 3 weeks.
Pressing
The skins are gently pressed and the juice is separate from the skins and seeds.
Pneumatic press (“air bag press”)
The grapes are filled in a cylindrical tank with a bladder in the middle that is filled with air and pushes the grapes against the wall, separating the juice from the skin.
- It can be filled with inert gas.
- It can apply different amount of pressure.
Basket press (“vertical press”)
The grapes are filled in a basked and pressed from above. The juice is collected on a tray below and transferred by pipe to another vessel.
- It cannot be filled with inert gas.
- It is gentler than Pneumatic press
- Hold smaller load, therefore requires more time and labour. Meaning is suited for premium wines only.
Horizontal screw press - inexpensive, high volume
- It is less gentle, requires batch pressing, and can take lots of time. Therefore is less popular.
Continuous press - inexpensive, high volume
Is continuously loaded for quicker pressing, however is less gentle.
Must adjustments
Enrichment
(before or during fermentation)
Generally used in cool climate.
Increase alcohol content by:
- Adding sugar (Chaptalisation), beet or cane.
Allowed in cooler EU areas.
- Adding grape concentrate
- Adding grape must
- Rectified concentrated grape must (RCGM)
Allowed in warmer EU areas.
- Processes of concentration (less wine to sell)
Reverse osmosis and vacuum evaporation (high initial cost due to expensive machines)
Cryoextraction (freezing must, removing ice)
More affordable.
Reducing alcohol
(before or after fermentation)
Generally used in hot climate.
Decrease alcohol content by adding water to the must. However, also dilutes the grapes aromas/flavour and acids.
Acidification
(preferred before fermentation to benefit from better integration and a lower pH)
Generally used in hot climate.
Increase acidity by:
- Adding Tartaric acid
- Citric acid (not permitted in EU)
- Malic acid (less used, it could lead to Malo)
- Lactic acid (after Malo, less harsh)
Deacidification
(before fermentation)
Generally used in cool climate.
Decrease acidity by:
- Adding Calcium carbonate or Potassium carbonate (Tartrates forms and precipitates)
- High tech Ion exchange
(high initial cost due to expensive machines)
Adding tannins
Powdered tannins helps to clarify the must, stabilise colour and improve mouthfeel.
Alcoholic fermentation
Is the conversion of sugar into Ethyl alcohol (ethanol), carbon dioxide and heat.
Carried out by yeast, anaerobically.
Yeast
(Saccharomyces cerevisiae - microscopic fungi)
Yeast releases:
- Volatile acidity (vinegar, nail polish remover)
- Glycerol (increase body)
- Wine aromatics from
Precursors (from compounds) such as Thiols (gooseberry), Terpenes (floral, grapey)
Yeast such as easters (banana), Sulfur compounds (rotten egg, rotten cabbage)
Ambient yeast
ADV:
- Can add aroma complexity
- can be unique to a place
- it is free
- can be use for marketing
DIS:
- Fermentation may start slowly, increasing volatile acidity and risk of spoilage organisms (such as Brettanomyces)
- Fermentation may take longer, increasing risk of stuck fermentation
- Not consistent
Cultured yeast
ADV:
- Fermentation is quicker, decrease volatile acidity and risk of spoilage organisms (such as Brettanomyces)
- Consistent
- Yeast strains can be tailored to the style of wine.
DIS:
- Lead to similar fruit expression
- it has a cost
Oxygen helps yeast to multiply before fermentation.
Yeast nutrients (phosphate or thiamine) may be added if nitrogen level are low as this can lead to the production of sulfur compounds (rotten egg, rotten cabbage)
Temperature
Warm start at the beginning of fermentation (25C) establish yeast population.
Cool: 12-16C - Fresh, fruity white and rose’
Promote and retain easters (fruity aroma/flavour)
Mid-range: 17-25C - Easy drinking, fruity red to retain easters and low tannins extraction.
Or less fruity white wines, usually barrel fermented.
Warm: 26-32C - Pronounced flavour concentration, high tannins red wines. Maximise phenolic (colour and tannins) extraction but can lose some fruity flavour.
Temperature are controlled and typically installed in vessels. This is done by either water of glycol jackets or by techniques such as pumping over.
Fermentation vessels
Stainless steel - High volume due cheaper price, hygiene and:
- high level of mechanisation (auto pumping over, temperature control, auto emptying, cleaning)
- Anaerobic
- range of sizes
- do not add flavour
Wood - more expensive, lose value over time.
- Retain heat well, but more difficult to control.
- Allow oxygen in
- Pores increase risk of spoilage organisms.
- Small barrels are used for red wines to manage cap.
Concrete - expensive
- High thermal (maintain heat well)
- Its egg shape permit natural lees stirring
Terracotta
Is in small use today.
Amphora (Georgia), Tinaja (Spain)
Malolactic conversion
MLF Malo
Lactic acid bacteria convert malic acid into lactic acid, carbon dioxide and heat.
Can be started by:
- adding lactic acid bacteria
- Temperature of 18-22C
- Moderate pH (3.3-3.5)
- Low total SO2
Can be avoided by:
- adding enzyme lysozyme (kills lactic acid bacteria)
- avoiding the above
- filtering lactic acid bacteria
The MLF Malo will cause
- Reduction in acidity and rise pH, resulting in softer and smoother style of wine
- Loss of colour
- Greater microbial stability, it prevents malolactic conversion from happening later.
- Loss of fruit character and addition of buttery notes and volatile acidity.
Usually Malo occur in barrels to stir the lees at the same time. However takes more time and monitoring as barrels may be at different temperatures.
Other producers Promote Malo at the same time as alcoholic fermentation to same time, money and selling earlier.
Post-fermentation Adjustments
Enrichment, Reducing alcohol, Acidification, Deacidification and Adding tannins same as before.
Removal of alcohol by:
- adding water to the must. However, also dilutes the grapes aromas/flavour and acids.
- Reverse osmosis.
Alcohol and water are filtered, distilled and blended back.
Costly.
- Spinning cone.
Volatile aroma are extracted, the alcohol is removed, the aroma are blended back.
High volume wines.
Colour
- Reduce colour by fining the wine
- Enhance colour intensity by adding grape-derived colouring agent (Megapurple)
