D1: Maturation Flashcards
Generally oxidation leads to a gradual reduction in many primary aromas and a development of _____
tertiary aromas such as dried fruits and nuts
- if well developed the this can enhance the quality of a wine
- if not this can result in reduction of quality
Additionally oxidation can influence the colour of wines:
1) white wines becomes darker, gradually becomming gold and then brown
2) young red: can result in greater stability and intensity:
- - anthocyans binds with tannins
* this protects anthocyanins from being absorbed by yeast lees or bleached by so2 additions
* * important for ligt coloured red wines such as PN
—- after much more extensive ageing, red wines gradually become paler and browner
For red wines oxidation also seem to result in the ____ of tannins.
Softening
- this may be positive for quality
- – not yet well understood, but may at least in part be linked to anthocyanin and tannin bonding
The speed of oxidation is influenced by the amount of oxygen exposure, the compounds in the wine and temperature, among other factors.
1) wine fully exposed to air (and hence oxygen): will generally oxidise quicker than when oxygen exposure is more gradual (kept in a large oak vat)
2) red wines can withstand a higher level of oxygen exposure than whites before any signs of oxidation are apparent due their higher content of anti oxidative phenolic compounds (eg tannins)
* this is why red wines are often matured longer than whites with 12-24 months pre bottling maturation and 6-12 for white
3) warm temp increasing the speed of oxidation reactions
A high level of oxidation is a key part of the style of some wines (such as oloroso sherry)
The oxidation evident from the brown colour of the wine and lack of fresh fruit on the palate replaced by nuts and dried fruits
- in this case the iwne is stored in barrels that are not filled up to the top allowing oxygen to the headspace of the barrel (ullage)
— more commonly for unfortified red and white wines, the exposure to oxygen is limited and has much slower and subtler effect
** too much oxidation in these wines is usually seen as a fault
what about wooden vessels and oxidative maturing ?
1) some oxygen is released from the pores of the vessel within the first month that the vessel is filled with wine
- - a very small amount is also passing through the gap between the staves and the bung hole
2) the time when the wine is the most exposed to oxygen is during transportation (racking, lees stirring or topping up when the bung is removed)
Some wine is generally lost during the maturation process in wooden barrels.
Water and alcohol in liquid form impregnate the wood
– within the staves of wood the water and alcohol turn to vapour (evaporate) and diffuse (verspreid) along the concentration gradient to the air outside the vessels
- this leads to a gradual concentration of the other components of the wine
- small vessels evaporate more wine than large
- – also the topping of small vessels leds to more oxygen exposure then in larger vessels
- —- the amount of oxygen that enter the barrel relative to the volume of wine is also larger for small barrels
- leading to quicker (but not extreme) oxidation
Maturing wine in barrels is costly, therefore micro oxygenation is a replacement technique:
1) bubbling oxygen into the wine
2) the dose is typically in units of mg/l per month
3) generally carried out in stainless steel tanks for a number of months post alcoholic fermentation
4) generally for inexpensive and mid priced wines (however now also on premium)
What does micro oxygenation do to the wine ?
1) increases colour stability and intensity, soften tannins, improve texture and reduce the presence of any unripe herbaceous flavours
2) it provides the effects of gentle exposure to oxygen more quickly than in wooden barrels
3) the rate of oxygen can be controlled much better than in oak barrels
4) if used in conjunction with oak alternatives (staves, chips) it also can integrate the influence of the oak
However, care must always be taken because the increasing oxygen levels in the wine can provide a more favourable environment for spoilage microbes such as
Acetic acid bacteria and brettanomyces
Wines are usually matured in stable cool temp to slow down the rate of oxidation and other reactions and lower chance of microbial spoilage.
1) whit wines: 8-12°c 46-54°f
2) red: 12-16°c 54- 61° f
* as they are less susceptible to the effects of oxidation
Stable cool temp give a slower maturation than warm temp 20°c and above due :
the effect of chemical reactions hat happens between the different compounds in the wine
Temp also determines what reactions can occur and how quickly various reactions will occur
* unfortunately, many of the reactions that benefit from warm temp are undesirable in terms of wine quality
Low humidity and warm temperatures increase the rate of wine loss.
this is undesirable as it reduces the volume of wine to sell
also:
- barrels need to be topping up more (greater cost of labour)
- risk for oxidation harmful for quality
Conditions of low humidity approximately 70% causes water to be lost at greater rate than alcohol and over time this can lead to a higher alcohol concentration in the wine, which in many instances may be seen as undesirable
- for these reasons, wines are usually matured in cool cellars of constant temperature and humidity
- temp and humidity control systems are common in modern cellars
- — many traditional cellars where build underground for this same reason
wooden vessels permit a slow exposure to oxygen during the wine’s maturation. newly made vessels contains various extractable compounds, including tannins and many aroma compounds, which can have a significant influence on the wine. the level and type of extracted from vessels depend on the following features of wooden vessels:
1) age of the vessel
2) size of the vessel
3) type of wood
4) production of vessel
Age of the vessel:
1) new wood contains various extractable compounds
- - each time a barrel is used the amount of extraction decrease
* a barrel loses about 50% of its new oak flavours during the first year of use
2) after four years of use the barrel will contribute very little, but still allow ingress of oxygen
3) the flavours of new oak can clash with aromatic grape varieties
4) where new oak is used it is typical as a proportion of the blend with wine that is stored in pre used barrels
Size of the barrel:
Small vessels, such as barriques 225l hold a relatively small volume of liquid compared to the surface area of the vessel.
– this means that any extraction from the wood and exposure to oxygen is greater in small vessels than large vessels such as foudres
Type of wood:
1) most commonly is oak:
- can easily be shaped into a barrel
- - makes containers that are watertight
- - positive effects on aroma flavour of the wine
- — different species of oak can have different characteristics
* most are from european oak (french, also hungarian, russian or slavonian, also american
- both eu and amerikan have significant levels of vanilin
- american have higher levels of lactones which gives coconut aromas to the wine
- – in general american oak haves an greater intensity of aromas/ flavours than european oak which is often subtler
- – european has more tannin
2) The production process for barrels from eu oak is more expensive than american (french vessels more expensive than american)
* american: 300€ -600€
* french: €600-1200
- - eu oak has to be split to create staves
- — american oak can be sawn
* ** american oak also grows significantly faster than european oak
3) thightness of the grain:
- more thightly grained wood: result of slower growth of tree
- - ex oak in continental climates grow slower (russia hungary) so thightes grains
- — wood with tight grain slow down extraction of aromas and flavours
* hungarian oak is gaining popularity in NY because it adds slowly tannins and gradual aroma compounds to their wines who are generally medium in body, alcohol and tann and flavour intensity (so no dominant oak characteristics
4) also chesnut wood, cherry and acacia
Production of the vessel:
1) wood needs to be seasoned: outside and can dure 2-3 years
- - lowers the humidity level
- - reduces bitter flavours
- - increase aroma compounds (such as those who give cloves)
2) heating the staves for bending
- - also transform the tannin and aroma compounds in the oak
- - temp and length of heat exposure is refered as toasting level
* light, medium or heavy toasted
* contributes notes of spice, caramel, toffee roasted nuts char and smoke
* * many are more pronounced at heavy toasting
- —- many winemakers let make the barrels to an house style (housestyle)
The level and type of compounds extracted from the vessel will also depend on the length of time that the wine is aged in the vessel:
1) the longer the more extrction of compounds and greater exposure to oxygen
2) some extraction is greater at different stages in the maturation process thats why it is not completely constant
*** size of the vessel, type age of wood and environment will also affect the extraction of aromacompounds
Why is barrel maturation expensive ?
1) expensive to buy
2) small barriques dont hold much wine so a lot of barrels are needed
3) monitoring and performing winemaking options as lees stirring is dificult in so much barrels
4) spoilage microbes like brettanomyces like to live in wood so meticulous cleaning and sanitation is needed
5) slow process, the wine can be stored for 1-2 years or even longer
6) in most cases the wine is sold when its packaged and reaches the market
For expensive reasons the winemaker may choose to use alternative to barrels:
1) oak chips and staves
- - can be attached in stainless steel vessels or concrete vessels
- — chips are generally in a sack whos left to soak in the vessel
- — also different species available and toasting levels (complexity)
2) micro oxygenation
Lees describes the sediment that settles at the bottom of a wine vessel. it is made up:
- dead yeast
- dying yeast and bacteria
- grape fragments
- precipitated tannins, nutrients and other insoluble compounds
the sediment that forms quickly after the end of fermentatin (24 hours) is called gross lees:
This is made of larger heavier particles
— smaller particles settle down more slowly called fine lees
the lees may be removed by removed by racking
1) the first after ferm removes gross lees
2) subsequent peridic racking helps to manage the levels of fine lees
—- some winemakers will choose to keep the wine in contact with the fine lees, this has several effects
