Topic 8 - Red and white table wine production

Question 1

What are the requirements of a grape receival system?

Answer 1

• That picking bins from the vineyard that can be easily unloaded with a minimum of damage to the grapes
• That the grapes are easily transferred into the crusher (via the grape receival bin / receival hopper)
• That it is easily cleaned and maintained

Question 2

What is the purpose of a crusher?

Answer 2

To break the berry skins with little pulping or other damage, and to efficiently seperate the stalks if this is desired.

Question 3

What are the advantages of destemming prior to crushing?

Answer 3

• Whole berries can be more easily maintained - Broken stems are not in contact with the must - Separated stems are less covered in juice

Question 4

After crushing what happens to the must?

Answer 4

After crushing, the must falls into a must hopper or sump from which it is pumped to the designated fermentation vessel.

Question 5

What are some additions that may be made at the crusher?

Answer 5

• Sulfur dioxide (added either as a solid, liquid, or gas)
• Pectolytic enzyme which is sometimes added at the crusher to facilitate rapid separation of white juice from the skins.
• Acid (usually tartaric acid) to increase acidity (reduce pH).

Question 6

What are some characteristics used to select yeast?

Answer 6

o Flavour characteristics
o Alcohol tolerance
o Nutrition requirements
o H2S production
o Fermentation rate

Question 7

What does fermentation on skins achieve when making red wine?

Answer 7

o Phenolic extraction
 Colour
 Astringency
 Bitterness

Question 8

During red fermentation, the skins form what at the top of the vessel and why?

Answer 8

During red fermentation, the skins form a dense ‘cap’ at the top of the vessel due to the carbon dioxide being produced.

Therefore the fermenter design needs to able facilitate the wetting and/or mixing of the cap in order for extraction.

The wetting and/or mixing also allows the ferment temperature to be dispersed evenly and help prevent some spoilage.

Question 9

What are three methods of cap management?

Answer 9

1. pump-over (where fermenting juice / wine pumped from bottom of the tank to the top where it can be sprayed over the cap)
2. punch down (or plunging) by hand (or foot) or mechanically
3. sprinklers (similar to pump-over – cap can be irrigated at regular intervals) mixing of the ferment with a roto-fermenter header boards which physically push cap under liquid level pressurised gas (air or nitrogen) systems such as Pulse Air.

Question 10

What happens to the marc after fermentation?

Answer 10

The marc (i.e. seeds and skins) need to be removed for pressing.

Question 11

Why is refrigeration important during fermentation in Australia?

Answer 11

Above 35C, some yeast strains can struggle to survive.

Question 12

Name 4 types of fermentation vessels.

Answer 12

• Open fermenter
• Closed fermenters
• Roto-fermenters
• Red fermenters

Question 13

What is carbonic maceration and what is its aim?

Answer 13

• The general aim of carbonic maceration is to produce a light-bodied wine which is suitable for early drinking with a soft structure and distinctive confectionary, berry flavour.
• For true carbonic maceration, sound uncrushed clusters of grapes are loaded into a closed vessel (best results are obtained if the vessel has been pre-filled with carbon dioxide gas), and then left for 1-2 weeks during which the grapes respire any remaining oxygen and eventually ‘drown’ in carbon dioxide.
• The colour then permeates from the skin cells into the grape flesh, and there is also some alcohol production, loss of acidity and flavour production characteristic of the technique.
• The grapes are then removed from the tank and pressed, and the resulting red, partly-fermented juice is treated as any other juice/wine after pressing.

Question 14

What is MLF?

What does it result in?

Answer 14

• Malolactic Fermentation (MLF) is the bacterial conversion of malic acid to lactic acid.
• MLF results in a reduction in acidity, improved microbial stability, and flavour stability.

Question 15

What is extracted during fermentation on skins?

When does peak extraction occur?

Answer 15

• Colour and other compounds
• Approx. 6 - 10 days

Question 16

What determines the timing of pressing?

Answer 16

• The timing of pressing depends on end of fermentation, amount of tannin extraction desired and often logistic decisions that depend on tank space.

Question 17

What is pressing?

Answer 17

• Usually the juice is drained off as ‘free run’ and the remaining wet skins are transferred to the press, generally manually (in small wineries) by screw conveyor or directly by gravity.

Question 18

What is a basket press?

Answer 18

These are the oldest and simplest form of press still used, and traditionally consisted of a basket of wooden slats seated in a steel juice-collecting tray.

Question 19

What is a horizontal screw press?

Answer 19

These presses work on the same principle as the screw-operated basket press except they are horizontal, with the basket able to be revolved in order to loosen the cake between pressure applications and also to enable the pressed marc to be emptied through doors in the basket.

Question 20

What is an airbag press?

Answer 20

The older types consist of a horizontal, rotatable slotted stainless steel basket, through the centre of which extends an inflatable rubber air bag.

More modern models of air bag presses are of the ‘tank press’ type , which consists of a fully-enclosed vessel within which is a membrane (the air bag) and juice collection channels.

Question 21

Why is whole bunch used in white wine production?

Answer 21

To reduce phenolic extraction.

Question 22

What are the benefits of juice clarification?

When does it occur?

Answer 22

• More varietal aroma (an absence of ‘solids’ character on the nose), less mouthfeel texture and a more even fermentation with less foaming.
• After pressing

Question 23

When is juice clarification sometimes skipped?

What styles of wine are typically made with clarified juice?

Answer 23

• Often full-bodied wines are made from less-clarified juice or even juice with complete solids without any clarification.
• For example, some Chardonnay wines, or perhaps barrel fermented Sauvignon Blanc (where varietal character is not part of the intended style) may be fermented without juice clarification.
• Light-bodied, aromatic wines such as Riesling, Semillon and Sauvignon Blanc are typically made with clarified juice.

Question 24

What are the four main methods of juice clarification?

Answer 24

• Settling
• Filtration
• Centrifugation
• Flotation

Question 25

Describe the settling method of juice clarification.

Answer 25

• Over a period of time grape solids will fall out of suspension naturally due to gravity.
• Juice is held in closed tanks at low temperature (desirably, less than 8-10°C) to minimise microbial activity and oxidation.
• Sufficient levels of sulfur dioxide (see below) are also required.
• When sufficient settling is achieved the clear juice is racked off the juice lees and then warmed prior to fermentation.

Question 26

Describe the filtration method of juice clarification.

Answer 26

• Filtration has not been traditionally used for juice clarification as most filter types (eg filter pads) do not have sufficient capacity for solids retention without blockage.
• The main use of filtration for juice clarification is the use of a rotary vacuum drum (RVD) which can recover juice from juice with a high solid content, such as the juice lees following cold settling.
• Rapid recent advancements in cross flow filtration also has also allowed the use of this technology for some juice clarification.

Question 27

Describe the centrifugation method of juice clarification.

Answer 27

• Continuous centrifuges are often used in large wineries where their main advantage is continuous running with low labour requirements.
• Juice or wine is fed into the outside of a rapidly-spinning rotor and then ‘up’ the gravity gradient to the centre of the rotor.
• Because of their greater density relative to the juice, the solids
  ‘settle’ to the outside of the rotor and are discharged as a sludge.
• The main disadvantages of centrifugation are the large capital cost and possible harsh treatment of the juice.

Question 28

Describe the flotation method of juice clarification.

Answer 28

• Small bubbles of nitrogen or carbon dioxide is introduced at the bottom of a tank of juice and carry suspended solids to the tank top.
• Bentonite, gelatine (or other protein phenolic agents – see below) and pectolytic enzymes are often used to facilitate the separation. - The process has the advantage of only taking a few hours to complete before the juice underneath can then be pumped out for fermentation in another tank.

Question 29

Why are premium quality aromatic whites generally fermented at low temperatures (12 - 18C)?

Answer 29

• High temperatures can causes loss of desirable fruit and yeast flavours.
• As fermentations are exothermic (ie heat is released), refrigeration needs to be available either as in-place cooling plates or coils, or as external heat-exchangers.

Question 30

Why is SO2 added at key points during the winemaking process?

Answer 30

It inhibits microbiological activity (especially bacteria) and helps minimise oxidation.

Question 31

What does bound SO2 mean?

Answer 31

When SO2 is added to juice or wine, a portion becomes chemically combined with other components such as sugars or fermentation by-products (acetaldehyde, pyruvic acid, ketoglutaric acid).

The portion that is not combined is known as free SO2.

Question 32

What is SO2 not added at pressing when making red wine?

Answer 32

Red wines may not have finished both alcoholic fermentation and malolactic fermentation (MLF) (see below) at pressing and therefore sulfur additions would not take place at this stage. Additionally white wines for which MLF was desired would also not have sulfur dioxide added until MLF was completed.

Question 33

What is a risk of not completing MLF before bottling?

Answer 33

When all malic acid is consumed the wine will not undergo a further malolactic fermentation in the bottle.

Question 34

Why is stabilisation completed?

Answer 34

For commercial acceptability, finished wines are normally expected to be stable to (i.e. free from) potassium bitartrate or protein precipitation

Question 35

How does chilling wine achieve potassium bitartrate stability?

Answer 35

Inducing crystallisation by chilling the wine to approximately 2 to -2 °C in the winery and then filtering out the crystals. Cream of tartar (which is actually KHT!) provides a site of nucleation to facilitate crystallisation.

Question 36

What is protein stability?

Answer 36

• Certain forms of grape protein in white wine are denatured and cause a haze when the wine is heated, e.g. in a hot room or car.
• Protein can be removed by bentonite fining to avoid this problem occurring in the bottled wine.
• Bentonite is a clay mineral which, when added to wine or grape juice, binds with grape protein and then falls out of suspension.
• This fining also has a side benefit of aiding general clarification and can be carried out during fermentation with the bentonite lees combining with the yeast lees.
• Protein instability is not generally a problem in red wines as these have a large amount of phenolic compounds which precipitate out the grape proteins.

Question 37

Why are fining agents such as casein, egg white and gelatine used?

Answer 37

To remove bitterness and/or astringency due to phenolic materials in wines.

Question 38

Describe phenolic fining?

Answer 38

The fining is added as an aqueous suspension and forms a protein-phenolic combination which falls out of solution.

Question 39

Why is copper sometimes used as a fining agent?

Answer 39

The addition of soluble copper ions, generally, as copper sulfate, in very small concentrations (about 1 mg/L) is often used as a ‘fining’ to remove hydrogen sulphide off aroma.

Copper ions form highly insoluble sulfides which are odourless and can be settled out and removed.

Question 40

What are the main requirements of storage vessels?

Answer 40

• they should not leak;
• they must be free of chemical or flavour contaminants;
• air must be excluded to avoid oxidation;
• temperature control, particularly cooling, is desirable;
• versatility of function is desirable, e.g. some fermenters are also used as storage vessels;
• they must be easily and effectively cleaned.

Question 41

What are the main types of storage vessel?

Answer 41

• Stainless steel tanks
• Synthetic containers
• Small wood barrels
• Large wooden vats and casks

Question 42

How can you avoid oxidation and microbiological spoilage during storage?

Answer 42

• Oxidation and microbiological spoilage can be reduced by excluding contact with air by minimising ullage (keeping the vessel full) and use of inert gases.
• Appropriate free/ molecular sulfur dioxide levels are also important at this stage of the winemaking process.

Question 43

What generally occurs prior to bottling in most commercial wineries?

Answer 43

Prior to bottling, most commercial wine is filtered with a variety of filtration types such as pads and/or membrane filters.