14. Maturation

Question 1

Why might a producer choose to store their wine in bulk?

Answer 1

Some winemakers producing young, fruity styles of wine choose to bottle only when an order from a customer has been placed, or they choose to ship the wine in bulk.

Question 2

What is the role of oxygen in maturation?

Answer 2

• Oxidation leads to a gradual reduction in many primary aromas and a development of tertiary aromas.
• Oxidation can influence the colour of wines
• For red wines; oxidation can lead to the softening of tannins

Question 3

What happens when a young red wine is exposed to oxygen?

Answer 3

Exposing a young red wine to oxygen can result in greater colour stability and intensity. In this reaction, anthocyanins bind with tannins, which, in turn, protect anthocyanins from being bleached by SO2 additions or adsorbed by yeast lees (i.e. the anthocyanins are not held as a thin layer on the lees, which would reduce the colour of the wine). This is particularly important for light-coloured red wines

After much more prolonged exposure to oxygen, all red wines gradually become paler and browner.

Question 4

What are the main factors influence the speed of oxidation in maturation?

Answer 4

• The amount of oxygen exposure
• The compounds in the wine
• Temperature; warm temperatures increase oxidation

Question 5

How does oxygen enter wooden vessels during the maturation stage?

Answer 5

• Some oxygen is released from the pores of the vessel within the first month it is filled
• A very small amount of oxygen continues to enter through the gaps between the staves and the bung hole
• The times when the wine is most exposed to oxygen in this process is any transfer of the wine, such as racking, lees stirring, or topping up in which the bung is removed.

Question 6

How does evaporation occur when maturing wine in wooden vessels?

Answer 6

Water and alcohol in liquid form impregnate the wood. Within the staves of wood, the water and alcohol turn to vapour (evaporate) and diffuse, along the concentration gradient, to the air outside
the vessel.
This leads to a gradual concentration of the other components of the wine

Question 7

Why are wines maturing in smaller barrels frequently topped up?

Answer 7

• Small vessels, such as barrels, have a large surface area to volume ratio, increasing the rate at which wine is lost.
• This means that barrels frequently need to be topped up with more wine to keep them full (and hence avoid ullage and excessive oxidation).
• The frequency of topping up leads to more oxygen exposure in these vessels than in much larger vessels.

Question 8

What is micro-oxygenation?

Answer 8

Micro-oxygenation involves bubbling oxygen through wine. The dose of oxygen is typically in units of mg/L per month. Micro-oxygenation is generally carried out in stainless steel tanks for a number of months post alcoholic fermentation.

Question 9

Why might a winemaker choose to micro-oxygenate their maturing wine?

Answer 9

Winemakers may use micro-oxygenation in stainless steel tanks as a cheaper alternative to wooden vessels.

Question 10

What are the advantages of micro–oxygenation?

Answer 10

• Micro-oxygenation is thought to increase colour stability and intensity, soften tannins, improve texture and reduce the presence of any unripe, herbaceous flavours.
• Additional benefits are that it provides the effects of gentle exposure to oxygen more quickly than barrel ageing without needing expensive barrels.
• The rate of oxygen exposure can be controlled much more tightly than it could be in a barrel.
• If used in conjunction with oak alternatives (such as chips or staves), it can also help to integrate the influence of the oak.

Question 11

What are the disadvantages of micro-oxygenation?

Answer 11

• The increasing oxygen levels in the wine can provide a more favourable environment for spoilage organisms such as acetic acid bacteria and Brettanomyces
• New technique. therefore research into which grape varieties or types of wines benefit from micro-oxygenation and how wines made by micro-oxygenation age in bottle over the long term (and whether there is any difference compared to the same wine matured in barrel) is lacking.

Question 12

At what temperatures are wines typically stored during maturation?

Answer 12

Red wines: 12-16°C (they are less susceptible to the effects of oxidation)
White wines: 8-12°C

Question 13

What conditions increase the rate of evaporation in wooen vessels during maturation?

Answer 13

Low humidity and warm temperatures

Question 14

What is the risk of low humidity in the cellar during maturation?

Answer 14

Low humidity and warm temperatures increase the rate of evaporation of water and alcohol in wine maturing in wooden vessels.

Low humidity (under 70%) can cause water to be lost at a faster rate than alcohol, which over time, can lead to a higher alcohol concentration in the wine. This can throw the wine out of balance.

Question 15

How does the age of a barrel influence it’s contribution of aromas to a maturing wine?

Answer 15

New wood contains various extractable compounds. 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.) By the time the vessel is on its fourth usage, it will contribute very little at all (but still allow ingress of oxygen).

Question 16

Why do smaller barrels contribute more aromas than larger barrels?

Answer 16

Small vessels, such as barriques (225 l), 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 in large vessels, such as foudres.

Question 17

Why is oak the most common type of wooden vessel used for maturation?

Answer 17

It can easily be shaped into a barrel and, importantly, makes containers that are watertight. Oak is also prized for its positive effects on the aroma/flavour and structure of the wine. Different species of oak have different characteristics, but it is possible for the same species of oak to show different characteristics depending on where it is grown.

Question 18

What species of oak are most popular for maturation?

Answer 18

European (French, Hungarian, Russian, Slavonian)
American

Question 19

What are the main differences between American an European oak>

Answer 19

• One of the key differences is that American oak has been found to contain much higher levels of lactones, which give aromas of coconut.
• In general, American oak tends to impart a greater intensity of aromas/flavours than European oak, which is often said to be subtler.
• By contrast, European oak tends to impart more tannin.
• Tighter grain (slower growth of the tree).
• European oak barrels (€600–€1200) is much more expensive than American oak barrels (€300– €600);

Question 20

Why are European oak barrels more expensive to produce than American oak barrels?

Answer 20

The cost of American oak barrels tends to range from €300– €600, whereas that for French oak barrels tends to range from €600–€1200.
European oak must be split to create staves, whereas American oak can be sawn. The ability to saw American oak means more vessels can be made from the same amount of oak.
American oak also grows significantly quicker than European oak.

Question 21

How does the tightness of the grain in oak barrels influence wine? Example?

Answer 21

Wood with a tight grain slows down the extraction of compounds compared with more coarsely grained wood, and can alter what particular compounds are most extracted.

For example, Hungarian oak, which tends to have a tight grain, is gaining popularity in New York State as an option that allows very gradual extraction of oak aroma compounds and tannins for their red wines so that they are not dominated by oak-derived characteristics.

Question 22

Give two examples of oak species that are known to provide barrels with a tight grain.

Answer 22

A more tightly grained wood is the result of slower growth of the tree. For example, oak trees grown in continental climates, particularly Russia and Hungary, tend to grow slowly and therefore have the tightest grains.

Question 23

Other than oak, what other wood can be used in wine production?

Answer 23

Chestnut
Cherry
Acacia

Question 24

Where is Slavonian oak from and what region is known for it’s use?

Answer 24

Slavonia is a region in north-eastern croatia.
Slavonian oak is commonly used in Italy, particularly for Nebbiolo and Sangiovese.

Question 25

What are the steps in barrel production?

Answer 25

1. Seasoning 2. Staves are selected, trimmed then bent into shape (fastened with a metal hoop). 3. Barrel toasting 4. The barrel heads are put in place, the barrel is sanded, the bunghole is cut, and the temporary hoops are replaced with permanent ones.

Question 26

What is meant by barrel seasoning?

Answer 26

Barrel seasoning typically takes place outside and lasts 2–3 years. This lowers the humidity levels in the wood, reduces bitter flavours and increases some aroma compounds, such as those that give flavours of cloves.

Question 27

How is oak shaped into a barrel?

Answer 27

* The staves are carefully selected and trimmed so that once bent, they fit together perfectly. (Oak is a natural product with a lot of tree-to-tree variation, so coopers rely on a blend of staves from different trees to improve consistency.) * The staves are positioned to form the circumference of the barrel and secured on one side using a temporary iron hoop. * Using fire and water, the staves are slowly bent by machine until they form the body of the barrel and can be fastened with another metal hoop. * This heating process imparts and transforms aroma and tannin to the barrel

Question 28

Outline the process of barrel toasting.

Answer 28

Barrel toasting, typically performed by a master cooper, requires skill. The cooper toasts the barrel by positioning it over a small fire for a precise amount of time, then moving it through a series of fires, each with a different temperature. The temperature and time spent over each fire determine the toast level.

Question 29

What is meant by 'toast level' in barrel production?

Answer 29

Toast level is a function of both time and temperature, and toast is often described as light, medium, medium-plus, and heavy. In general, higher toast oak has less oak lactone and tannin and more grilled, smoky, toasty aromas. The concentration of volatile phenols and other aroma compounds increases with toast, though heavy toasting can drive off these aromas

Question 30

What factors influence the level and type of aroma compounds extracted from wooden vessels during the maturation process?

Answer 30

* Age of the vessel * Size of the vessel * Type of wood * Production of the vessel * Length of time in wood

Question 31

Why is barrel maturation expensive?

Answer 31

* Barrels are expensive to buy * Small barrels (such as barriques) do not hold much liquid (225L) 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, and therefore it is not uncommon to store the wine for 1–2 years or even longer. In most cases the wine is only sold when it is packaged and reaches the market, therefore return on investment is slow

Question 32

What are oak staves?

Answer 32

An alternative to barrels when flavours of oak are desired. Oak staves can be attached to the inside of the stainless steel or concrete vessel, or they can float in the wine.

Question 33

What are oak chips?

Answer 33

An alternative to barrels when flavours of oak are desired. Oak chips are generally placed in a permeable sack, which is left to soak in the wine.

Question 34

What are the advantages of using oak staves or chips instead of barrels?

Answer 34

* They are much cheaper than purchasing barrels * For both options it is possible to purchase different species of wood and different seasoning and toasting levels * Can be added to a large tank of wine (therefore less labour intensive) * Their large surface area means they are quick to have an effect * The amount needed for the desired stylistic effect can also be finely tuned * Can be used alongside micro-oxygenation to replicate gentle oxidation

Question 35

What is lees?

Answer 35

Lees describes the 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

Question 36

What is the difference between gross lees and fine lees?

Answer 36

* **Gross lees** is the sediment that forms quickly after the end of fermentation (within the first 24 hours). This is made up of the larger, heavier particles. * **Fine lees** is made up of a sediment from smaller particles that settle more slowly.

Question 37

How is lees removed?

Answer 37

Racking The first racking after fermentation generally removes the gross lees, and then subsequent periodic racking helps to manage the levels of fine lees.

Question 38

What is autolysis?

Answer 38

After fermentation, the yeast cells die very slowly and break down, releasing compounds that contribute flavours, body and texture to the wine.

Question 39

How does autolysis alter the wine?

Answer 39

* Autolysis releases compounds that contribute flavours * 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. * In white wines, where the effects of lees are generally more significant, descriptors can include yoghurt, dough, biscuit or toasted bread.

Question 40

How does lees ageing protect white wine?

Answer 40

Lees ageing helps in the stabilisation of white wine against unstable proteins that can cause hazes. They also help to protect the wine from oxygen, helping to maintain a slow, controlled oxidation during maturation and lowering the need to use SO2 during this time.

Question 41

What happens when the layer of lees is too thick?

Answer 41

It can produce volatile reductive sulphur compounds (considered to add complexity in small amounts, a fault in larger amounts).

Question 42

How do lees assist in malolactic conversion?

Answer 42

Lees provide nutrients for microbes, and therefore can assist the growth of lactic acid bacteria for malolactic conversion. It also encourage the development of spoilage organisms such as Brettanomyces.

Question 43

How does lees ageing increase the cost of the final wine?

Answer 43

* Lees ageing may increase the time the wine is stored before release, prolonging the ROI (not applicable if the wine is undergoing oak ageing anyway). * Wines aged on lees (particularly gross lees) require regular monitoring, may be stirred; both of which increase labour costs

Question 44

What is racking?

Answer 44

* The process of transferring wine from one vessel to another with the aim of removing sediment from the wine (eg lees, grape sin, tartartes etc). * The wine is removed from the original vessel through a valve near the bottom of the vessel (above the top of the sediment) and pumped or poured into the top of a new, clean vessel.

Question 45

How might a winemaker protect the wine from oxygen when racking to remove sediment?

Answer 45

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.

Question 46

In what ways can a producer blend wine?

Answer 46

* From different grape varieties * From different locations * From different grape growers/businesses * From different vintages * Blending wines that have been treated differently in the winery (oak ageing, lees stirring, free run/press juice) * When wines are in different vessels for logistical reasons

Question 47

What are the seven key reasons for blending wines?

Answer 47

1. Balance 2. Consistency 3. Style 4. Complexity 5. Minimise faults 6. Volume 7. Price

Question 48

Give two examples of why a wine is blended to improve it's **balance**.

Answer 48

A batch of wine from a warmer vineyard or that has been picked late may be blended with a batch of wine from a cooler vineyard or that has been picked early to fine tune acidity levels. Merlot provides body and ripe, plummy fruit to a blend with Cabernet Sauvignon, which, when not fully ripe, can be too astringently tannic on its own.

Question 49

What does it mean to blend wine for **consistency**?

Answer 49

To reduce bottle and vintage variation

Question 50

Give an example of how wines can be blended to minimise faults.

Answer 50

If wine in one barrel is showing significant volatile acidity, that wine may be sterile- filtered to remove acetic acid bacteria and then blended into a larger volume of un-faulty wine to lower the concentration and sensory perception of acetic acid.

Question 51

Give an example where wines are blended for price reasons.

Answer 51

Chardonnay and Pinot Noir typically cost a lot more than Pinot Meunier. Producers are increasingly blending a higher proportion of Pinot Meunier into their Champagne blends.

Question 52

What are the reasons a producer might **not** blend wines?

Answer 52

* Producer may want to produce a 'single vineyard' wine, which can not only maintain the flavour of the fruit and terroir, but also a benefit from a marketing POV. * Some grape varieties have pronounced and distinctive flavours and do not benefit from blending with another grape varieties (eg Sauvignon Blanc).

Question 53

Outline the blending process.

Answer 53

The blending process generally begins with blending trials using measuring cylinders and small volumes of wines to distinguish the proportion of each wine in the favoured blend before conducting on a much larger scale. This is a process that requires a high level of skill and experience.

Question 54

When is blending best carried out?

Answer 54

Before stabilisation in case any instabilities arise from the blend; for example, tartrate stability is dependent on pH level, and this can be affected by blending wines with different pH levels.