C7 - Common Elements In Winemaking And Maturation (reviewed) Flashcards
On a basic level, what is alcoholic fermentation?
Yeast converts sugars in the grape to alcohol
What is the next basic stage of winemaking after alcoholic fermentation?
The wine needs to be stored prior to packaging and sale
Broadly speaking, what are natural wines?
Wines made with minimal intervention
Describe the constituents of a grape
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
Describe the importance of oxygen in wine making
- 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
What is the argument against anaerobic winemaking?
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
What is the implication on maturation of Protective/anaerobic winemaking
Wines that have been protected from oxygen during winemaking rarely if ever benefit from oxygen contact during maturation
How are anaerobically vs. aerobically made wines stored?
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
What happens to flavours in wine during deliberate oxidation/maturation?
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)
How large is a barrique?
225L
How may the effect of barrel oxidation be further enhanced?
- If the container is not completely full.
- Wine will develop aromas of caramel, toffee and nuts
- Example: Oloroso Sherry, Rutherglen Muscat, Tawny Port
Discuss the use of Sulfur Dioxide in a winery
- 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
Discuss the role of oak ageing in wine making?
- 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
What are the four major factors to consider when choosing oak for maturation?
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
What are alternatives to replace the role of oak in wine making?
- 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.
Discuss inert vessel
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
Discuss Grape processing
-
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
Discuss different types of wine press?
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
Discuss press juice
- 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
How is grape juice commonly referred to?
Must
What is the term for the level of sugar in grape juice?
Must weight
Describe adjustments
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
What is RCGM?
Rectified Concentrated Grape Must
A colourless, odourless, syrupy liquid
What is chaptalisation?
When sugar from sources other than grapes is added as a form of enrichment
Name an adjustment which is very difficult
Removing sugar
Discuss Alcoholic Fermentation
- 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
Which yeast species is responsible for the majority of wine fermentations? Why is this used?
Saccharomyces cerevisiae
Due to its tolerance of relatively high alcohol levels and SO2
Discuss yeast choices for a winemaker has
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
Discuss temperature management during fermentation
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
Discuss MLF
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
Discuss Lees formation
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
Discuss pre-bottling maturation
- 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)
Discuss blending
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
List some variations of blends that a winemaker may create
- Using different grape varieties
- Different vineyard plots
- Separating press fractions
- Fermenting/maturing in different vessels
- Allowing only a proportion to go through MLF
- Different vintages
Discuss clarification
Main techniques used: Sedimentation, Fining and Filtration
Discuss sedimentation
- 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
Discuss fining
- 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
Discuss Filtration
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
Discuss Stabilisation
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
What are the advantages/disadvantages of glass bottles?
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
What are other packaging options?
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
What factors may dictate the type of closure which is used for a bottle?
- 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
What does an airtight closure allow?
Retention of fresh fruit flavours
What is the most widely used bottle closure?
Cork
What is the major benefit of cork as a wine closure?
It allows very small amounts of oxygen to enter the wine, thus allowing the development of sometimes desired tertiary flavours
What are the two problems with cork-closed wines?
Risk of oxidation
Risk of cork-taint
- Cause by Trichloroanisole (TCA)
- Gives wine a mouldy, cardboard-like aroma
Hat are synthetic corks made from?
A form of plastic
They are generally designed for wines intended for early consumption
Who has championed the use of screw caps?
Producers from Australia and New Zealand
What are the advantages of screw caps as closures?
- 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
Within what time are the majority of wines best consumed?
One year
What happens to wines not intended for ageing when kept in bottle for more than a year?
They lose their primary fruit flavours
