D1 Maturation 1: Oxygen, Wood, Lees; Blending, Finishing, Stabilization

Question 1

What are three key factors that can influence wine during maturation?

Answer 1

1. Oxygen;
2. New wood;
3. Lees.

Question 2

How does oxygen influence wine aromas during maturation?

Answer 2

• Reduces many primary aromas;
• Helps develop tertiary aromas.

Question 3

How does oxygen affect the color of white and red wines?

Answer 3

When exposed to oxygen, white wines become darker (gold, then brown);

When exposed to oxygen, red wines become lighter (paler, then brown).

Question 4

Which of the following is the speed of oxidation directly related to?

• The color of the wine
• The style of the wine
• The amount of oxygen exposure, the compounds in the wine, and temperature

Answer 4

The amount of oxygen exposure, the compounds in the wine, and temperature.

A wine that sees more gradual oxygen exposure will oxidize less quickly than a wine that is fully exposed to air.

Question 5

Why can red wines often mature longer than white wines?

Answer 5

Red wines can take a higher level of oxygen exposure than white wines due to their higher content of anti-oxidative phenolic compounds (such as tannins).

Question 6

How is wine exposed to oxygen when it is being matured in wooden barrels?

Answer 6

• Oxygen passes through the gaps between the staves and the bung hole;
• Some oxygen is released from the pores in the barrel within the first month that the vessel is filled with wine;
• During racking, lees stirring, and topping up.

Question 7

Why does topping up in small barrels lead to more oxygen exposure than in larger barrels?

Answer 7

Because small barrels have a large surface area-to-volume ratio, water and alcohol evaporate more quickly which forces their need to be topped up more frequently to keep them full, with oxygen entering the barrel every time the bung is removed.

Question 8

Describe the micro-oxygenation technique.

Answer 8

• It’s a cheaper way to oxygenate wine by forcing oxygen bubbles through the wine;
• It is generally carried out in stainless steel tanks over several months after alcoholic fermentation.

Wines at every price point can practice micro-oxygenation.

Question 9

What are the advantages of micro-oxygenation?

Answer 9

1. Increases color stability and intensity;
2. Softens tannins and improves texture;
3. Reduces unripe, herbaceous flavors;
4. Provides gentle exposure to oxygen more quickly than barrel aging (don’t need expensive barrels, reducing costs);
5. Control rate of oxygen exposure better than in a barrel;
6. If used with oak alternatives (e.g. chips or staves), can help integrate the influence of oak flavors.

Question 10

What is a big potential disadvantage of micro-oxygenation?

Answer 10

Increasing oxygen levels in wine can provide a more favorable environment for spoilage microbes (e.g. acetic acid bacteria and Brettanomyces).

Question 11

Why are wines usually matured in cool cellars with constant temperature and humidity?

Answer 11

• Slows down the rate of oxidation;
• Slows down chemical reactions;
• Lowers the chance of microbial spoilage;
• Provides slower maturation process;
• Slows the rate of wine loss;
• Higher humidity means less evaporation (and slower alcohol concentration).

Question 12

A new oak barrel loses about ___% of its new oak flavors during the first year of use.

Answer 12

50%

Question 13

Oak barrels will impart little to no oak flavor at all by their ___ year of use.

Answer 13

4th

It will still allow ingress of oxygen, though.

Question 14

How many liters do barriques hold?

Answer 14

225 L

This means that any extraction from the wood and exposure to oxygen is greater in barriques than in foudres.

Question 15

What are three positive attributes of oak barrels?

Answer 15

1. Easily shaped;
2. Makes watertight containers;
3. Has significant levels of vanillin (imparts vanilla aromas in wine).

Question 16

What is the key difference between American oak and European oak?

Answer 16

American oak has higher level of lactones (which impart coconut aromas)

Question 17

European oak tends to impart more ____ than American oak.

Answer 17

Tannin

Question 18

Which oak grows faster: American or European oak trees?

Answer 18

American

Question 19

To make staves, American oak can be ___ whilst European oak must be ____.

Answer 19

American oak = sawn

European oak = split (more expensive)

Question 20

1. The slower the growth of oak trees, the ____er the grain.
2. The tighter the grain, the ____er the extraction of oak compounds.

Answer 20

1. Tighter
2. Slower

Question 21

What three things happen to wood during its ‘seasoning’ stage?

How long does seasoning take and where does it take place?

Answer 21

1. Reduction in humidity levels in the wood;
2. Reduction in bitter flavors;
3. Increase of some aroma compounds.

Takes place outside and lasts 2-3 years

Question 22

What are the toasting categories for oak?

Answer 22

1. Light toast;
2. Medium toast;
3. Heavy toast.

Question 23

What flavor characteristics does toasted oak contribute to wine?

Answer 23

• Spice;
• Caramel;
• Roasted nuts;
• Char;
• Smoke.

These notes become more pronounced at heavy levels of toasting.

Question 24

What exactly is ‘toasting’?

Answer 24

The temperature and length of heat exposure at which the oak staves are exposed.

Question 25

Generally, the longer a wine is aged in a wooden vessel the greater:

Answer 25

1. The extraction of compounds from the wood;
2. The exposure to oxygen.

Question 26

On what factors does the level of wood extraction depend?

Answer 26

• Type/source and age of wood;
• Size of the barrel;
• Toast level of the barrel;
• Length of time in barrel;
• Environment in the cellar.

Question 27

What alternatives to barrels exist for winemakers?

Answer 27

• Oak chips
• Oak staves

Question 28

Lees is a term for the sediment that settles on the bottom of a wine vessel.

What is that sediment made up of?

Answer 28

• Dead & dying yeast;
• Bacteria;
• Grape fragments;
• Precipitated tannins;
• Nutrients;
• Other insoluble compounds.

Question 29

What are the gross lees?

Answer 29

The sediment that forms right after the end of fermentation (within the first 24 hours).

They are larger, heavier particles.

Question 30

How are lees removed?

Answer 30

By racking

Question 31

The first racking after fermentation removes the ___ lees, and then subsequent periodic racking helps to manage the levels of ___ lees.

Answer 31

First racking removes gross lees;

Subsequent rackings remove fine lees.

Question 32

What is the name of the process when yeasts die and break down, releasing compounds that contribute flavor, body and texture to the wine?

Answer 32

Autolysis

Question 33

What are some of the other compounds that autolytic compounds combine with?

How do those combinations affect the wine?

Answer 33

1. Phenolic compounds in the grapes
   
   • reducing color and softening tannins;
2. Wood tannins and wood flavors
   
   • ​​reducing astringency and modifying wood flavors.

Question 34

What happens if the gross lees layer is too thick and not controlled?

Answer 34

• Volatile, reductive sulfur compounds can be produced (e.g. hydrogen sulphide {rotten egg smell});
• Can encourage the development of spoilage microbes (e.g. Brettanomyces).

Question 35

What are two protective benefits of lees aging?

Answer 35

• Stabilization of the wine against unstable proteins that can cause hazes later on;
• Protects the wine from oxygen;
  
  • slow, controlled oxidation during maturation reduces the need for SO₂.

Question 36

What is bâtonnage?

Answer 36

Stirring of the lees

Question 37

What is racking, and what is its aim?

Answer 37

Transferring wine from one vessel to another with the aim of removing sediment from the wine.

This sediment may be gross lees, fine lees or other solid material in the wine that has fallen to the bottom of the vessel, such as tiny fragments of grape skin or tartrate crystals.

Question 38

Racking can be either oxidative or reductive.

Explain how.

Answer 38

When done oxidatively, winemakers will increase oxygen exposure by deliberately splashing the wine without any inert gas involved; good for red wines.

When done reductively, inert gas will flush the hose first and then push the wine through that same hose; good for aromatic or fruity white wines.

Question 39

When is blending typically carried out?

Answer 39

Just before finishing and packaging

Question 40

When winemakers blend wine, what exactly can be blended?

Answer 40

1. Different grape varieties;
2. Grapes from different locations (different vineyards, different regions or even different countries);
3. Different vintages;
4. Grapes that have had different treatment in the winery (e.g. wine fermented in stainless steel blended with wine fermented in new oak);
5. Grapes that have been treated equally in the winery but are in different vessels for logistical reasons.

All of this depends on the wine’s PDO, regulations, and laws around what can and cannot be blended.

Question 41

What are the main reasons for blending wines?

Answer 41

• Balance;
• Consistency;
• Complexity;
• Style;
• Minimize faults;
• Volume;
• Price.

Question 42

What does the term “finishing” a wine mean?

Answer 42

Preparing it for its final packaging, which can include:

• clarifying;
• stabilizing;
• correcting SO_2;
• bottling.

Question 43

How far ahead of bottling is the final wine assembled?

Answer 43

8 weeks to 4 months

Question 44

How far ahead of bottling are final adjustments made to a wine?

Answer 44

8 weeks

Question 45

How far ahead of bottling are protein stability and tartrate stability checked and treated, if necessary?

Answer 45

4 weeks

Question 46

How far ahead of bottling are sweetening agents added to a wine?

Answer 46

1-2 weeks

Question 47

How far ahead of bottling is free SO₂ adjusted, if necessary?

Answer 47

24 hours

Question 48

Name four processes used to clarify wine.

Answer 48

1. Sedimentation;
2. Centrifugation;
3. Fining;
4. Filtering.

Question 49

What is the most common way of clarifying wine?

Answer 49

Filtration

Question 50

Describe the sedimentation process.

Answer 50

Clarification naturally begins when wine is stored in cool cellar conditions.

The wine is allowed to stand and particles (with higher density than wine) will form a sediment at the bottom of the container over time. The wine can then be racked off, leaving the sediment behind.

The bigger the vessel, the more rackings needed so as to avoid a super thick layer of sediment.

Question 51

The sedimentation process is most suitable for what price point of wine?

• Inexpensive to moderate priced
• Moderate priced
• Premium or super-premium priced

Answer 51

Premium or super-premium priced

Sedimentation takes time to carry out, and this has a cost to the winemakers as the wine cannot be sold until it is ready.

Question 52

Describe the centrifugation process.

Do small, medium, or high-volume wineries use this process?

Answer 52

Wine is spun at a high rotational speed causing matter in suspension to be separated out, thereby clarifying it. It is most effective with wines with a lot of matter in suspension.

Only used in high-volume wineries to spread the considerable cost of buying the machine.

Question 53

What is the purpose of fining?

Answer 53

To accelerate the process of precipitating suspended materials out of a wine.

Question 54

What are fining agents made from?

Answer 54

Proteins or minerals

Question 55

What does fining do to a wine?

Answer 55

Helps clarify and stabilize the wine; if fining isn’t employed, the wine could later become hazy in the bottle

Question 56

What does fining remove from a wine?

Answer 56

1. Unstable colloids (microscopic particles) that are too tiny to be removed by filtration;
2. Harsh tannins in red wines;
3. Browning in white wines.

Question 57

A fining agent must have the:

• same charge
• opposite charge

of the colloid to be removed.

Answer 57

Opposite charge

Question 58

What are three categories of common fining agents?

Answer 58

Those that remove:

1. Unstable proteins;
2. Phenolics that cause unwanted color and bitterness;
3. Color and off-odors.

Question 59

Bentonite:

1. What is it made of?
2. What does it do?
3. What are the effects of using it?

Answer 59

1. A form of clay which has a strong negative charge;
2. Absorbs unstable proteins and unstable colloidal coloring particles;
3. Effects:
   
   • some color loss if used in red wines;
   • produces large amounts of sediment, so wine can be lost when it is racked off.
   • Minimal effect on the flavor and texture of wine;

Question 60

Bentonite can be used to:

• Fine must only
• Fine wine only
• Fine must as well as wine

Answer 60

Fine must as well as wine

Question 61

Why isn’t bentonite suitable for removing tannins or bitter phenolics?

Answer 61

Because bentonite has the same charge as tannins; and if they’re the same charge, they won’t be attracted to one another.

Question 62

What colors of wine are most often fined with bentonite?

Why?

Answer 62

White and rosé wines

• proteins stick together and give these wines an undesirable haze, especially if the wine warms in transit

In red wines, these proteins bind with tannins and are removed when the wine is racked.

Question 63

Name 6 fining agents that remove phenolics that cause unwanted color and bitterness.

Answer 63

1. Egg Whites;
2. Gelatin;
3. Casein;
4. Isinglass;
5. Vegetable proteins;
6. PVPP.

Question 64

Egg whites:

1. In what form are they used?
2. Used mostly for what style of wine?
3. Are they harsh or gentle on the wine?
4. Why are they problematic?

Answer 64

1. Fresh or powdered form;
2. Used for high-quality reds because of their ability to remove harsh tannins and clarify;
3. Gentle to the wine;
4. They are an allergen, and must be declared on the label if the wine is sold in the EU and other territories if above a specified limit.

Question 65

What is gelatin and from what is it derived?

1. What does it do?
2. What does it remove?
3. Is it vegetarian?

Answer 65

It’s a protein extracted from pig skins and animal bones by boiling.

1. Helps clarify wine;
2. Removes bitterness + astringency in reds and browning in whites, but may strip the wine of color and flavor so use minimum effective amount;
3. Not vegetarian.

Question 66

Gelatin can be used to:

• Fine must only
• Fine wine only
• Fine must as well as wine

Answer 66

Fine must as well as wine

Question 67

Casein:

1. What is it?
2. What does it remove?
3. What’s problematic about it?

Answer 67

1. Milk-derived protein;
2. Removes browning from white wines + somewhat clarifies wines;
3. It’s an allergen, so must be on the label in some territories.

Question 68

Casein can be used to:

• Fine must only
• Fine wine only
• Fine must as well as wine

Answer 68

Fine must as well as wine

Question 69

Isinglass:

1. What is it?
2. What color wine is it mostly used on and why?
3. What makes it problematic?
4. Is it suitable for vegetarians?

Answer 69

1. A protein collagen derived from fish bladders. It comes in sheets, strips, chips, or coarse powder;
2. Mostly used in white wines to improve brightness and clarity;
3. If too much is used, wine can smell fishy and it can produce fluffy lees which clog filters and create haze;
4. Not suitable for vegetarians.

Question 70

Vegetable proteins:

1. From what are they derived?
2. Useful for what kind of wine?

Answer 70

1. Derived from potatoes or legumes;
2. Useful for vegan and vegetarian wines.

Question 71

PVPP (Polyvinylpolypyrrolidone):

1. What is it?
2. What does it remove?
3. What can it reduce or improve in red wines?

Answer 71

1. Insoluble plastic, used in powder form;
2. Removes browning + astringency from oxidized white wines;
3. Rarely used on red wines, but can reduce astringency + brighten color.

Question 72

Name a fining agent that removes color and off-odors.

Answer 72

Charcoal

Note!: Charcoal over-fines easily and can remove desirable aromas and flavors in addition to color and off-odors, so careful use is paramount.

One approach is to treat a small batch of the affected wine and then blend it with the rest of the wine.

Question 73

Describe filtration.

Answer 73

It is a technique used to physically remove solids suspended in wine by passing the wine through a filter that has porous layers that trap the solid particles, thereby clarifying the wine.

Question 74

What are the two main types of filtration?

Answer 74

1. Depth filtration;
2. Surface filtration.

Question 75

Describe depth filtration.

Answer 75

Wine that is heavy in particulates is passed through a thick filter with lots of irregular channels, and particles are trapped in the depth of the material that forms the filter.

Depth filters do not clog easily, but if too much wine is forced through it for too long the filter will pass some particles (it is not an absolute filter).

Question 76

What are the two types of filters used in depth filtration?

Answer 76

1. Diatomaceous earth filters;
2. Sheet filters.

Question 77

The most common form of depth filtration is by using ____.

What is it made of?

Answer 77

Diatomaceous earth

Diatomaceous earth (aka Kieselguhr, DE) is derived from a sedimentary rock composed of the skeletons of diatoms (microscopic algae) that lived 60-100 million years ago.

Once it has been processed, it is pure silica and inert.

Question 78

Which two filters use DE?

Are they oxidative or reductive processes?

Answer 78

1. Rotary vacuum filters use DE to filter very thick, cloudy wine (e.g. wine with lees). This is an oxidative process as the drum is exposed to air;
2. Enclosed DE filters do the same thing, but can be flushed with an inert gas (nitrogen) to avoid oxidation (reductive).

Question 79

Sheet filters are also known as “___ and ___” or “___” filters.

Answer 79

“Plate and frame” or “pad” filters

Question 80

1. How do sheet filters work?
2. Are they cheap or expensive?

Answer 80

1. Wine is passed through a sheet of the filtering material;
   
   • The more sheets in the filter, the faster the wine is filtered because any portion of wine only passes through one sheet;
   • Sheets of very fine grade can be used to remove remaining yeasts at bottling;
2. It’s expensive to initially install them, but the sheets are affordable.

Question 81

Describe surface filtration.

Answer 81

Surface filters trap particulates larger than the pore size of the filter being used.

The pore sizes used in surface filtration tend to be smaller than the pore sizes used in depth filtration (often less than 1 micron), so they generally perform more slowly than using a depth filter.

Question 82

Surface filters are also termed ___ filters.

What do they do?

Answer 82

Absolute filters

Surface filters catch particles bigger than the filter’s pore size.

Question 83

What are the two types of surface filters?

Answer 83

1. Membrane filters
2. Cross-flow filters

Question 84

Membrane filters are a very common form of filtration during the ___ process.

Why?

Answer 84

Bottling/packaging process

• they are used as a final precaution right before bottling to ensure the wine is thoroughly clear and microbiologically stable (yeast and bacteria completely removed).

Question 85

Membrane filters are also known as ___ filters.

Answer 85

Cartridge filters

Question 86

Cross-flow filters, aka tangential filters:

1. What are they best used for?
2. What’s unique about them?
3. Are they cheap or expensive?

Answer 86

1. Best for quickly filtering wine with lots of particles or lees;
   
   • solid particles cannot pass through them;
2. As wine passes through the filter it also cleans the surface of the filter;
3. Expensive, so best for large or well-funded wineries.

Question 87

Because membrane filters – one type of surface filter – have such tiny pores (< 1 micron), what do you have to do prior to using them?

Answer 87

Pre-filter the wine to remove heavy solids first, usually by depth filtration, otherwise the membrane filters will clog quickly.

Question 88

As an umbrella term in winemaking, what is stabilization designed to do?

Answer 88

To stop a wine from developing faults in bottle, e.g. haziness, clouds, bubbles, browning, or deposits.

If wines are not stabilized, the finished wine risks having undesirable effects.

Question 89

What are three main areas in which winemakers want stability in their wines?

Answer 89

1. Protein stability;
2. Tartrate stability;
3. Microbiological stability.

Question 90

What are tartrates?

Answer 90

Harmless crystals that precipitate out of a finished wine, principally made of potassium bitartrate and, less frequently, calcium tartrate.

They look like tiny, clear, glass-like crystals.

Question 91

What are the six methods used to prevent tartrate crystals from forming?

Answer 91

1. Cold stabilization;
2. Contact process;
3. Electrodialysis;
4. Ion exchange;
5. Carboxymethylcellulose (CMC);
6. Metatartaric acid.

Question 92

To cold stabilize a wine, the wine must be held at what temperature and for how long?

Answer 92

-4°C (25°F) for ~8 days

This is so that tartrate crystals form and can be filtered out before bottling.

Question 93

If a winemaker is going to cold stabilize their wine, what step must they perform prior to cold stabilization, and why?

Answer 93

Wines must be fined prior to cold stabilization so that colloids can be removed – because colloids can prevent tartrate crystals from forming.

Question 94

Which tartrate crystal precipitates out during cold stabilization?

• Potassium bitartrate
• Calcium tartrate

Answer 94

Potassium bitartrate

Question 95

What is the contact process in regards to tartrate stability?

Answer 95

Wine is seeded with finely powdered potassium bitartrate crystals which act as nuclei for further crystal growth, and the wine is then chilled to 0°C (32°F).

Contact process is less expensive than cold stabilization and faster (usually 1-2 hours); the wine will be stable at the temperature down to that at which it was treated.

Question 96

Describe the electrodialysis process.

Answer 96

This process is used for tartrate stabilization (mostly in the EU). It uses a charged membrane to remove selected potassium and calcium ions and, to a smaller extent, tartrate ions.

After costly initial investment, the total costs are lower than cold stabilization, plus it uses less energy and it’s faster.

Question 97

Describe the ion exchange process.

Answer 97

This process is used for tartrate stability, but it does not remove tartrates; instead, it replaces potassium and calcium ions with hydrogen or sodium ions, which will not precipitate out of the solution.

This process isn’t permitted in some territories because it replaces the potassium with sodium which is seen as unhealthy, even though the resulting sodium levels in the wine are well below the legal limit.

Question 98

Describe carboxymethylcellulose (CMC) use when performing tartrate stabilization.

Answer 98

CMC is cellulose that is extracted from wood and prevents tartrates from developing to a visible size.

CMC is widely used on cheap white and rosé wines, and it is not suitable for red wines because it reacts with tannins and causes haze.

It is much less expensive than chilling, and CMC keeps wines stable for a few years.

Question 99

Describe the use of metatartaric acid during tartrate stabilization.

Answer 99

This compound prevents the growth of potassium bitartrate and calcium tartrate crystals, reducing the need for cold stabilization.

However, the compound is unstable. Its positive effect is lost over time, especially when wine is stored at high temperatures (25–30°C / 77–86°F).

It is a quick and easy process that tends to be used more for red wines (white and rosé wines in the same category will use CMC instead as it is more effective and longer lasting).

Question 100

When a winemaker performs microbiological stabilization on a wine, what are they removing from the wine?

Answer 100

Yeasts and bacteria, which, if left in the wine, could potentially restart fermentation in the bottle.

Question 101

Wines that have residual ____ are more at risk of starting to referment in the bottle.

Answer 101

Sugar

Question 102

What are the two ways in which wines may be treated for microbiological stabilization?

Answer 102

1. They go through sterile filtration, thereby removing all yeasts;
2. Adding sorbic acid and SO₂, which inhibit yeast from growing.

Question 103

Name two microbes that can live in wine (read: in an environment that’s low in pH with high alcohol levels).

Answer 103

1. Lactic acid bacteria;
2. Brettanomyces (a spoilage yeast).

Question 104

If malolactic conversion wasn’t completed or if a wine wasn’t filtered to remove lactic acid bacteria, what can potentially happen to the finished wine?

Answer 104

Malolactic conversion can start up again in the bottle, causing cloudiness in the wine.

Question 105

How is wine treated for Brettanomyces?

Answer 105

• The winemaker can try filtering first to see if that helps;
• Treat with DMDC (dimethyl dicarbonate, commercial name: Velcorin) before bottling, which inactivates Brettanomyces.

Question 106

Winemakers will perform a full chemical analysis on their wine prior to employing any final finishing options prior to bottling.

What are the major things winemakers are analyzing?

Answer 106

• Alcohol;
• Residual sugar;
• Total SO₂;
• Free SO₂;
• Dissolved oxygen;
• Dissolved CO₂.

Question 107

What are the general ranges of free SO₂ in white, red, and sweet wines?

Answer 107

• White wines: 25–45 mg/l
• Red wines: 30–55 mg/l
• Sweet wines: 30–60 mg/l

Question 108

What can a winemaker do if they find the level of dissolved oxygen in their wine is too high?

Answer 108

The winemaker can flush the wine with an inert gas to remove the oxygen, a process called sparging.

Question 109

Blending red and white wines to make rosé is not allowed in many geographical indications within the EU except for these 2 regions:

Answer 109

1. Champagne;
2. Franciacorta.