Maturation: oxygen, wood, lees, blending Flashcards
Maturation for young, fruity or aromatic styles:
Protected from oxygen by S02 or by blanketing with inert gases, likely to be finished and packaged shortly after the end of fermentation.
Or bottle only when an order from a customer has been placed (stored in bulk =more convenient then store stacks of bottles)
Options during Maturation:
- Oxygen exposure
- New wood
- Yeast lees
- Blending
Not all of these are always used, depending on the style of wine that is being aimed for
Effects of Oxygen during maturation:
Oxidation reactions play a significant role in the way aroma and phenolic compounds evolve in the wine:
- Leads to a gradual reduction in many primary aromas and a development of tertiary aromas, such as dried fruits and nuts
- Influence the colour of wines (white wines become darker / young red wine can result in greater colour stability and intensity = anthocyanins bind with tannins, which, in turn, protects anthocyanins from being bleached by SO2 additions or adsorbed by yeast lees)
- Result in the softening of tannins, which may be positive for quality
The speed of oxidation is influenced by:
- the amount of oxygen exposure (size and type of vat)
- the compounds in the wine (red wines can withstand a higher level of oxygen exposure due to their higher content of anti-oxidative phenolic compounds (tannins)
- temperature (warm temperatures increasing the speed of oxidation reactions)
Wood vessels and oxygen:
- slow, gradual exposure to oxygen
- Some oxygen is released from the pores in the vessel within the first month
- Small amounts continues to pass through the gaps between the staves and the bung hole
- wine is most exposed to oxygen during racking, lees stirring or topping up
- Small vessels = large surface area to volume ratio, increasing the rate at which wine is lost. (need to be topped up with more wine to keep them full to avoid ullage
Micro oxygenation:
- cheaper alternative to barrel ageing
- involves bubbling oxygen through wine (typically in units of mg/L per month)
- Generally carried out in stainless steel tanks for a number of months post alcoholic fermentation
- increase colour stability and intensity
- soften tannins
- improve texture
- reduce the presence of any unripe, herbaceous flavours.
- Gentle exposure to oxygen more quickly than barrel ageing without needing expensive barrels
- Rate of oxygen exposure can be controlled much more tightly
- Can also help to integrate the influence of the oak alternatives (oak chips / staves)
- increasing oxygen levels in the wine can provide a more favourable environment for spoilage organisms such as acetic acid bacteria and Brettanomyces
- Relatively new technique = Research regarding the aging potential of these wines is lacking
Role of wood in maturation:
- Permit a slow exposure to oxygen
- Contains various extractable compounds including tannins and many aroma compounds, depending on:
- age : Each time the barrel is used, the amount of extraction decreases because fewer extractable compounds remain (A barrel loses about 50 per cent of its new oak flavours during the first year of use)
- size : Extraction from the wood and exposure to oxygen is greater in small vessels than in large vessels (because of wine to surface ratio)
- type of wood
- production of the vessel
Maturation: role of wood
Type of wood of the vessel
Oak is the most common:
- It can easily be shaped into a barrel
- makes containers that are watertight
- has positive effects on the aroma/flavour and structure of the wine
- Different species: European oak (typically French, but also Hungarian, Russian or Slavonian) or American oak.
- Both European and American = high levels of vanillin (aromas of vanilla)
- American oak has been found to contain much higher levels of lactones (aromas of coconut)
- American oak tends to impart a greater intensity of aromas/flavours than European oak, which is often said to be subtler.
- European oak tends to impart more tannin.
Another variable related to the type of wood is the tightness of the grain.
- A more tightly grained wood = slower growth of the tree (oak trees grown in continental climates, particularly Russia and Hungary, tend to grow slowly and therefore have the tightest grains)
- Wood with a tight grain slows down the extraction of compounds compared with more coarsely grained wood
Cost:
- American oak = €300– €600
- European oak = €600–€1200
- European oak must be split to create staves, whereas American oak can be sawn = more vessels can be made from the same amount of oak.
- American oak also grows significantly quicker than European oak.
Maturation: role of wood
Production of the wooden vessel:
- seasoning 2-3 years outside: this lowers the humidity levels in the wood, reduces bitter flavours and increases some aroma compounds, such as those that give flavours of cloves
- heating the staves so that they can be bent into shape: also transforms the tannins and aroma compounds in the oak.
- The temperature and length of heat exposure is referred to as the** level of toasting,**
- barrels categorised as either light-, medium- or heavy- toasted. Toasting contributes notes of spice, caramel, roasted nuts, char and smoke
Other types of wood used for vessels:
chestnut, cherry and acacia, are occasionally used
Costs of maturation in wood:
- Barrels are expensive to buy.
- Small barrels do not hold much liquid, which means that hundreds of these vessels may be necessary, even in modest-sized wineries.
- Monitoring the wine in each separate barrel and performing any winemaking operations, such as lees stirring or racking, is labour intensive.
- Spoilage organisms such as Brettanomyces like to live in wood and therefore meticulous cleaning and sanitation is also needed.
- Barrel maturation is a slow process (1–2 years or even longer) = return on investment is slow.
Describe oak alternatives:
- Oak staves: can be attached to the inside of the stainless steel or concrete vessel, or they can float in the wine.
- Oak chips: generally placed in a permeable sack, which is left to soak in the wine.
- For both options it is possible to purchase different species of wood and different seasoning and toasting levels.
- Much cheaper
- Can be added to a large tank of wine (therefore less labour intensive) and their large surface area means they are quick to have an effect.
- The amount needed for the desired stylistic effect can be finely tuned.
- Micro-oxygenation can be used alongside oak alternatives to replicate the gentle oxidation of barrel maturation as this helps integrate the oak flavours.
Describe the role of Lees in still wine maturation
- Lees = sediment that settles at the bottom of a wine vessel. It is made up of dead yeast, dying yeast and bacteria, grape fragments, precipitated tannins, nutrients and other insoluble compounds
- Gross Lees: sediment that form quickly at the end of femrnetation in the first 24h (the larger, heavier particles)
- Fine lees: smaller particles that settle more slowly
- After fermentation, the yeast cells die very slowly and break down (autolysis), releasing compounds that contribute flavours, body and texture to the wine. Some of these compounds bind with phenolic compounds
in the grapes, reducing colour and softening tannins.
Compounds from the lees also bind with certain extractable components of the wood, such as wood tannins and flavours, and can therefore reduce astringency and modify the flavours from the wood.
The effect of Lees aging on white wines:
- In white wines: Descriptors can include yoghurt, dough, biscuit or toasted bread.
- Helps in the stabilisation against unstable proteins that can cause hazes.
- Protect the wine from oxygen, helping to maintain a slow, controlled oxidation during maturation and lowering the need to use SO2 during this time.
- If the layer of lees is too thick, particularly a problem for gross lees, it can produce volatile, reductive sulfur compounds.
- At certain concentrations, some of these compounds can add complexity (e.g. giving aromas of struck match and smoke). However, if not controlled, these compounds may contribute unpleasant aromas, such as the smell of rotten eggs, a fault termed reduction
- Lees provide nutrients for microbes, and therefore can assist the growth of lactic acid bacteria for malolactic conversion, but also encourage the development of spoilage organisms such as Brettanomyces.
Racking:
- Process of transferring wine from one vessel to another with the aim of removing sediment from the wine (gross lees, fine lees or other solid material: tiny fragments of grape skin or tartrate crystals).
- Racking can be an oxidative process.
- Some makers of red wine will increase the oxygen exposure by deliberately splashing the wine.
- It is also feasible to protect the wine from oxygen during this time, which may be preferential for aromatic or fruity wines, by using pressure from inert gas to push the wine out through a hose into the new vessel, which would have been flushed with an inert gas.
- Racking may be carried out once or several times during the maturation process, depending on how long the wine is stored, whether it is stored with or without lees and whether the winemaker wants to increase oxygen exposure by racking.
Blending:
- mixing together of two or more batches of wine:
- from different grape varieties
- from different locations (from different vineyards, different regions or even different
countries) - from different grape growers or businesses that sell grapes, must or wine
- from different vintages
- that have been treated differently in the winery (e.g. white wine made from free run juice
and white wine made from press juice, or wine matured in oak with wine that has been
stored in stainless steel or concrete) - that have been treated equally in the winery but are in different vessels for logistical
reasons (e.g. unless a wine is made in very small quantities, wine fermented or matured in barrels will need to be blended together to make up the required volume). - can take place at any time but is most often carried out just prior to finishing and packaging
