C7 - Common Elements In Winemaking And Maturation (reviewed)

Question 1

On a basic level, what is alcoholic fermentation?

Answer 1

Yeast converts sugars in the grape to alcohol

Question 2

What is the next basic stage of winemaking after alcoholic fermentation?

Answer 2

The wine needs to be stored prior to packaging and sale

Question 3

Broadly speaking, what are natural wines?

Answer 3

Wines made with minimal intervention

Question 4

Describe the constituents of a grape

Answer 4

Seeds and stem:

• Both contain tannins
• Seeds contain high levels of bitter oils
• Stems are only available to the winemaker if hand harvested

Skin

• The skin and the area immediately underneath, contain high levels of flavour compounds (containing the grape’s signature character)
• It contains tannins, and colour compounds

Tannins

• A large number of chemical compounds are classed as Tannins
• At Véraison they taste very bitter and astringent, as grapes ripen, bitterness and astringency fall

Bloom

• The waxy surface that covers the skin of a grape.
• It contains yeast that can be used for fermentation

Pulp

• Water - largest constituent
• Sugar - second largest constituent
• Acid - Tartaric and Malic acid

Question 5

Describe the importance of oxygen in wine making

Answer 5

• Oxigen can react with Grape juice and many of the component parts of a wine
• Oxidation represents the biggest threat to a winemaker wanting their wine to be dominated by primary fruit characteristics

​Impact on wine:

• Too much oxidation can make the wine lose much of its fruit flavour and smell stale.
• In extreme cases, bacteria can use the oxygen to turn the wine to vinegar

Oxidation managed with:

• Night harvest: cooler => effect of oxygen is reduced because chemical reactions occur more slowly at lower temperatures
• Chilling the grapes before processing
• Using antioxidants (e.g. SO2) and
• Keeping oxygen contact to a minimum
• Protective/anaerobic winemaking: Filling airtight winery equipment with carbon dioxide or nitrogen before they are used

Question 6

What is the argument against anaerobic winemaking?

Answer 6

Some argue that the resultant wines may be bland or uninteresting and that a higher level of oxygen contact helps to develop complexity and character

Question 7

What is the implication on maturation of Protective/anaerobic winemaking

Answer 7

Wines that have been protected from oxygen during winemaking rarely if ever benefit from oxygen contact during maturation

Question 8

How are anaerobically vs. aerobically made wines stored?

Answer 8

Anaerobically

• In inert airtight vessels which are kept completely full
• Vats made from stainless steel or cement lined with epoxy-resin

Aerobically

• Wooden vessels that are normally made of oak
• Oak is watertight but not airtight
• Mild oxygen permeability of oak can help to soften tannins in red wines and gives more flavour complexity

Question 9

What happens to flavours in wine during deliberate oxidation/maturation?

Answer 9

Primary

• Primary fruit flavours gradually fade
• Tertiary characters start to develop, such as leather and earth

Colour

• Red wines become paler and gain a hint of brown
• White wines become deeper in colour and gain a hint of orange

Factors

• Size of vessel and Length of time stored are the main factors influencing the amount of deliberate oxidation a wine receives
• Smaller barrels have a greater oxidative effect (larger surface area of wood to wine ratio)

Question 10

How large is a barrique?

Answer 10

225L

Question 11

How may the effect of barrel oxidation be further enhanced?

Answer 11

• If the container is not completely full.
• Wine will develop aromas of caramel, toffee and nuts
• Example: Oloroso Sherry, Rutherglen Muscat, Tawny Port

Question 12

Discuss the use of Sulfur Dioxide in a winery

Answer 12

• Can cause allergic reactions, even at low levels
• It is regulated by law
• Quality-conscious winemaker want to keep SO2 levels as low as possible and it can make wines seem harsh and lacking in fruit
• Used for Antioxidant and Antiseptic effects

Antioxidant effect:

• SO2 levels must be constantly monitored and topped up
• By protecting wine from oxidation, SO2 can become ‘bound’ and lose its ability to have any further protective effect

Antiseptic

• SO2 is toxic to the many strains of yeast and bacteria that can cause unwanted flavours in wine
• Principal fermentative yeast are resistant to a certain level of SO2

Question 13

Discuss the role of oak ageing in wine making?

Answer 13

• Impact on the wine
  
  • Slight oxidation (Primary
  • Tannins -
  • Structure/textural complexity
  • Flavours - Toast, Vanilla, Smoke, Cloves Hygiene
• Challenge -
  
  • Very difficult to keep wooden vessels free of yeasts, bacteria and moulds
• Different types of vessels may be used to enhance complexity in their wines - as oak vessels differ widely in their characteristics

Question 14

What are the four major factors to consider when choosing oak for maturation?

Answer 14

Species and origin of oak

• Flavour can change, even within a species of oak
• European oak has broadly similar characteristics no matter which country it’s from - finest oak considered to be from France

Size

• Smaller vessels such as Barrique (225L) or Pièce (228L) have much greater ratio of wood surface to wine volume so gives more flavours than last vessels (up to 2000L)

Production of oak barrels

• Most important is Toasting - temperature and length of heat exposure.
• Heating transforms the tannins and the flavour compounds in oak - giving notes of Sweet spice and Toast

Age of the barrel

• A winemaker not use new oak to give subtler oak flavours as the effect of toasting diminishes each time a barrel is used

Question 15

What are alternatives to replace the role of oak in wine making?

Answer 15

• Oxidative effects of barrel ageing can be replicated by adding small, controlled quantities of oxygen to the wine vessel
• Oak aromas and tannins can be added by using oak planks or small oak chips, which are much cheaper.

Question 16

Discuss inert vessel

Answer 16

Inert vessels do not add flavour to the wine or allow oxidation

Majority are Stainless steel, Concrete or Glass bottles Use for Fermentation or Temporary storage of wine after it is finished

Stainless steel:

• Used by most modern winery vessels
• Easy to keep clean
• Can be made into any shape and size
• Can incorporate temperature control mechanisms (Sleeves on the outside of the vessels or internal coils through which cold or hot liquid can be circulated)

Concrete vessels:

• Lined with Epoxy resin to provide an inert waterproof barrier
• Was commonly used before stainless steel vessels
• Less easy to clean and maintain
• The thick concrete shells help to regulate temperature during fermentation and maturation without the need for expensive equipment

Question 17

Discuss Grape processing

Answer 17

• Grape processing:
  
  • Grapes arrive at winey and receive their first dose of SO2
  • They may be individually checked and sorted for unripe and rotten grapes
• Destemming: Grapes are destemmed in most cases (if machine harvested, they arrive without a stem)
• Crushing:
  
  • Grapes are crushed to break the skin and liberates a quantity of Free run juice
  • Need to be gentle, because if the seeds are crushed, they will release bitter oils and tannin
• Pressing
  
  • Separates the liquid and solid constituents of the grape
  • Happens before fermentation for whites, after for red wines
  • Seeds need to remain undamaged

Question 18

Discuss different types of wine press?

Answer 18

Vertical press “basket press”

• Traditionally all press were vertical
• The pressure on the grapes comes from above, using a screw or lever
• Champagne is particularly known for its vertical presses

Pneumatic press

• An inflatable rubber tube within a perforated, horizontal stainless steel cylinder
• Allow to apply pressure over a larger area in a controllable way (compared to vertical press) some are built within a closed tank to minimize amount of oxygen in contact with the juice

Question 19

Discuss press juice

Answer 19

• Liquid released at the start of pressing is very different to liquid released at the end
• Factions are different pressings of grape juice/wine
• Different factions may treated individually and blended in different proportions to create a certain style

Question 20

How is grape juice commonly referred to?

Answer 20

Must

Question 21

What is the term for the level of sugar in grape juice?

Answer 21

Must weight

Question 22

Describe adjustments

Answer 22

Adjustment can be done before, during or after fermentation for sugar, acid or alcohol

Sugar adjustment

• Depending on level of sugar in the juice, winemaker may decide to carryout Enrichment by adding RCGM before or during fermentation
• This Enrichment in turn rises the level of alcohol
• If Enrichment is abused, the wine may become hard and thin as there will be insufficient flavours to balance the artificially elevated alcohol
• Enrichment is forbidden in many parts of the world and when allowed it is strictly controlled
• When Enrichment uses sources of sugar other than grapes such as Beet, the process is called Chaptalisation.
• Other option: Remove water from must but it concentrates everything else (tannins, acid, flavour, faults) and reduce volume that can be made Removing sugar is very difficult

Acids adjustments

• Acids can be increased by adding tartaric acid in powder form
• Permitted warmer countries of Europe and common in many hot countries around the world
• Wine be de-acidified by adding an alkali

Alcohol adjustment

• Removing alcohol is possible with modern machinery

Question 23

What is RCGM?

Answer 23

Rectified Concentrated Grape Must

A colourless, odourless, syrupy liquid

Question 24

What is chaptalisation?

Answer 24

When sugar from sources other than grapes is added as a form of enrichment

Question 25

Name an adjustment which is very difficult

Answer 25

Removing sugar

Question 26

Discuss Alcoholic Fermentation

Answer 26

• Sugar + yeast => Alcohol and CO2 (and heat, flavour compounds)
• Minimum temp to start is 5°C
• Naturally stop when all the sugar has been consumed by the yeast
• Fermentation is controlled by choice of yeast and by managing Temperature

Fermentation may stop earlier:

• Yeast run out of nutrients
• Temperature reaches over 35°C
• Combination of high sugar and alcohol - if sugar levels are very high, fermentation may not even start

Wine maker can stop fermentation by

• Killing yeast with SO2 or a grape spirit
• Removing yeast (by filtering the yeast out after temporarily halting fermentation by chilling the must to below 5°C

Question 27

Which yeast species is responsible for the majority of wine fermentations? Why is this used?

Answer 27

Saccharomyces cerevisiae

Due to its tolerance of relatively high alcohol levels and SO2

Question 28

Discuss yeast choices for a winemaker has

Answer 28

Choice of ambient yeast strains (on the grape bloom), or cultured strains

Ambient yeast

• Can produce complex flavours in the final wine
• Cannot control exactly which yeast strains are present
• There may be some variation between batches of grapes

Cultured strains available yeasts

• Strains of S. Cerevisiae that have been specifically selected because they consistently perform and produce attractive flavours are commercially available
• Can limit the potential complexity of the wine

Question 29

Discuss temperature management during fermentation

Answer 29

Temperature management has made a huge contribution to the quality and consistency of modern winemaking

• Temperature control during fermentation is easier today as many vats have their own cooling/heating system
• Pumping over also helps released excess heat

If fermenting wine becomes too hot, yeasts are killed

By controlling temperature, the winemaker can influence the wine’s flavours

Lower temperatures fermentation:

• Avoids the loss of most volatile aromas (which often have a floral character)
• Encourage the development of fruity aromas in white wines

Higher temperatures fermentation:

• Necessary for the extraction of colour and tannins from black grape skins

Question 30

Discuss MLF

Answer 30

Malolactic Fermentation:

• Starts once alcoholic fermentation has finished
• Lactic acid bacteria convert tart malic grape acid into softer lactic acid

​Impact of MLF on the wine

• Softens and reduces acidity
• Creates buttery flavours
• Produces CO2

Encouragin/avoiding MLF

• Encouraged by raising the temp. of the wine and not adding SO2
• Avoided by storing at cool temp, using of SO2 and by filtering out the bacteria

Question 31

Discuss Lees formation

Answer 31

Gross Lees

• After fermentation particules consisting of dead yeast cells and grape fragments are in the wine and usually heavy enough to fall to the bottom of the vessel within a few hours forming a sediment known as Gross Lee
• if left in the wine can cause unpleasant aromas

Fine Lees

• Smaller particules may settle down more slowly and are know as fine lees
• Removed gradually through the wine making process
• Winemaker may keep the fine lees during pre-bottle maturation to add extra flavours and a richer texture

Question 32

Discuss pre-bottling maturation

Answer 32

• Winemaker may bottle the wine after only a few months of storage in inert vessels to preserve as many primary fruit aromas as possible
• To benefit from ageing, wine needs to have sufficient tannins, acidity and alcohol but also flavours that will develop in an interesting way
• The vessel can affect the wine’s flavours by adding oak flavours or allowing the wine to oxidise
• Over time, wine components can react with each other, altering flavour or balance (and sometimes creating sediment in the vessel, which is periodically removed)

Question 33

Discuss blending

Answer 33

Blending can happen at any stage but usually after fermentation or during maturation

It is subject to local laws and regulations

Blending aims to achieve 3 things: Improve balance, Attain consistency or a certain style

Improve balance

• e.g. for red wine, free run wine may be blended with press wine to increase tannins in the final product

Attain consistency

• Wines matured in small barrels can develop in subtly different ways and may be blended together in a large vat to smooth out inconsistencies
• Variations may arise due to differences in fruit (harvested at different times) or inconsistencies may arise during winemaking

Achieve a certain style

• A winemaker can achieve ‘house style’ by creating as many blending options as possible during the winemaking process

Question 34

List some variations of blends that a winemaker may create

Answer 34

1. Using different grape varieties
2. Different vineyard plots
3. Separating press fractions
4. Fermenting/maturing in different vessels
5. Allowing only a proportion to go through MLF
6. Different vintages

Question 35

Discuss clarification

Answer 35

Main techniques used: Sedimentation, Fining and Filtration

Question 36

Discuss sedimentation

Answer 36

• Sedimenation: Gross lees settle in a deposit at the bottom of the vessel
• Racking:
  
  • Once sediment settled, the wine is gently pumped into another vessel, leaving the sediment behind
  • Racking may be repeated several times during maturation
• Natural sedimentation is very slow and it can be accelerated by putting wine in a centrifuge but the equipment is very expensive

Question 37

Discuss fining

Answer 37

• Some hazes or deposits only appear in the bottle later on, once small wine constituents clump up together to become finally visible
• Fining is adding a fining agent that will accelerate this process to be able to remove the clumps by filtering them out.
• Fining is widely practiced but some winemakers decide to opt out as they believe it can adversely affect flavours and texture

Question 38

Discuss Filtration

Answer 38

A process that physically removes particles from a wine as it is passed through a filter

Performed after fermentation, during maturation and before bottling

Depth filtration

• Filters are made from a thick layer of material
• As wine passes through the filter, the solid parts become trapped
• It can handle very cloudy wines and remove gross lees

Surface filtration

• Filters resemble very fine sieves
• Solid particles are trapped on the surface of the filter as wine passes through
• Cons: Filters are very expensive and clog very easily so generally winemakers use depth filtration first
• Sterile filtration (Just before bottling)
  
  • Pores in a surface filter that are small enough to remove yeast and bacteria
  • Some winemakers believe that filtration can negatively affect a wine’s character, especially its texture

Question 39

Discuss Stabilisation

Answer 39

A wine is considered stable if over a specific time, it changes in a slow, predictable manner.

Fining can be considered a stabilisation process as it aims to produce a predictable outcome after bottling

Tartrate stability

• Tartaric acid crystals (Tartrates, clear for white, purplefor red wine) can form as tartaric acid is less soluble in wine than in grape juice
• Crystals spoil the appearance of the wine
• Formation is accelerated in cool temperatures
• Winemaker may force tartrate formation by chilling the wine to below 0°C and filtering them out

Microbiological stability

• Many yeast and bacteria can spoil a wine and make it undrinkable so it is important to keep winery equipment sterile
• Fortified wines are not affected as their alcohol levels are toxic for all microorganisms
• Highly resistant to microbiological spoilage - dry, high-acid wine that has undergone MLF
• Highly prone to microbiological spoilage: Low acid, low alcohol, no MLF and some residual sugar
• Treatment: SO2 or Sterile filtration

Oxygen stability - risk can be reduce by

• minimising oxygen contact
• keeping SO2 topped up
• flushing bottle with CO2 or nitrogen before filling to eliminate oxygen

Question 40

What are the advantages/disadvantages of glass bottles?

Answer 40

Advantages

• Portable
• Cheap
• Quite strong
• Oxygen impermeable
• Do not impart flavours to wine

Disadvantages - Heavy and rigid

• Weight - adds to transport costs
• Rigid:
  
  • half-full bottle will contain air
  • cannot be packed to make best use of the available space
• Counteracting measure:
  
  • Some producers are using lighter bottles
  • Some bottle in or closer to the destination country

Question 41

What are other packaging options?

Answer 41

Plastic bottles:

• They are slightly oxygen permeable and wines may lose their freshness within a matter of months

Bag-in-box wines:

• Advantage - The bag collapses as wine is drunk, preventing air from entering
• Disadvantage: The plastic bag is still oxygen permeable
• Must be consumed within 18 months

Question 42

What factors may dictate the type of closure which is used for a bottle?

Answer 42

• Ease of use
• Which closures a bottling line is designed to use
• For bottles intended for maturation, it must allow the wine to mature positively

Question 43

What does an airtight closure allow?

Answer 43

Retention of fresh fruit flavours

Question 44

What is the most widely used bottle closure?

Answer 44

Cork

Question 45

What is the major benefit of cork as a wine closure?

Answer 45

It allows very small amounts of oxygen to enter the wine, thus allowing the development of sometimes desired tertiary flavours

Question 46

What are the two problems with cork-closed wines?

Answer 46

Risk of oxidation

Risk of cork-taint

• Cause by Trichloroanisole (TCA)
• Gives wine a mouldy, cardboard-like aroma

Question 47

Hat are synthetic corks made from?

Answer 47

A form of plastic

They are generally designed for wines intended for early consumption

Question 48

Who has championed the use of screw caps?

Answer 48

Producers from Australia and New Zealand

Question 49

What are the advantages of screw caps as closures?

Answer 49

• They do not taint wine
• They provide an impermeable seal from air
• They therefore preserve fruit flavour in wine longer than cork
• Some screw caps have been designed to have some oxygen permeability

Question 50

Within what time are the majority of wines best consumed?

Answer 50

One year

Question 51

What happens to wines not intended for ageing when kept in bottle for more than a year?

Answer 51

They lose their primary fruit flavours