Element three - Maturation, Treatments and Bottling, Stabilisation.

Question 1

Stabilisation is a umbrella term for all winemaking operations designed to stop wine do what?

Answer 1

Developing faults in bottle, haze, clouds, bubbles or deposit.

Question 2

A perfectly clear wine may become unstable when exposed to following conditions! (3)

Answer 2

1. aeration, ex. during bottling
2. Light, shop windows.
3. Low or high temp during transport or storage

Question 3

The three main instability problems in wine are liked to:

Answer 3

1. tartrate instability
2. oxidation
3. microbial spoilage
   other exist but way less common.

Question 4

Potassium-bitartrate can be a problem in wine, why?

Answer 4

during or after the wine process, forming small crystals, harmless but can offend consumers. Fall during fermentation and can be racked away but in cases of not naturally cool cellars the potassium-bitartrate will crystallise in bottle or undergo cold stabilisation prior to bottling.

Question 5

Cold stabilisation is done how?

Answer 5

cooling the wine to -4° and -8° (dependent of leval of alcohol) and stored for up to 8 days. Crystals will form and fall to the bottom of the tank.

Question 6

Contact process is cold stabilisation 2.0, how?

Answer 6

by adding Potassium Bitartrate in crystal form it act like a nuclei for further crystals growth.

Question 7

Gum arabic and metatartaric acid is what and work how?

Answer 7

a protective colloid that prevents tartrate crystals from growing big enough to be seen. only last for less then a year, used for bulk wine.

Question 8

What would be a problem with calcium tartrate and how do you solve it?

Answer 8

if used calcium carbonate (de-acidification) or calcium bentonite (clarification) during the winemaking the high levels can create crystals, but only very slowly.
ion-exchange or electro-dialysis could be used.

Question 9

Ion-exchange is not allowed in the Eu, why and how is it used?

Answer 9

wine rich in potassium or calcium is passed through a resin of sodium iond, potassium or calcium is stuck and sodium enter the wine and will not form crystals.
Banned due to health concerns about to high levels of sodium in wine. Will also alter the aroma and taste of the wine.

Question 10

Oxidation of grape must or wine involves what?

Answer 10

Bonding of oxygen molecules to oxidisable compounds present in the must or the wine.

Question 11

When oxidised what happens to the wine?

Answer 11

Colour will change to brown and dull, aromas and flavours are destroyed, often being replaced with sherry-like aromas and bitterness will increases.

Question 12

What are some factors that will make a wine oxidate? (8)

Answer 12

1. action of polyphenol oxidase and laccase enzymes.
2. presence of yeast and acetic acid bacteria
3. level of phenolic substrates
4. amount of oxygen dissolved in the wine/must
5. PH (Lower the Ph, more protective the SO2)
6. SO2 consentration
7. Temperature, (lower the temp the slower the reaction rate but the more dissolved oxygen will be present)
8. catalysts such as copper ions.

Question 13

In grape must, oxidation is due to?

Answer 13

Chemical reaction between the phenolics in the must and the oxygen in the air. Polyphenol oxidase occurs in grape when laccase is produced by grey rot or Botrytis on the berries.

Question 14

Free sulfur dioxide should be a minimum of ___ after the alcoholic fermentation.

Answer 14

20 mg/L

Question 15

if a wine is browning it is likely to be the result of laccsase action, what is the only treatment for laccase activity?

Answer 15

pasteurisation

Question 16

the prevention of browning is usually achieved by?

Answer 16

storing at low temperaturs, addition of sulfur oxide and exclusion of air by inert gas.

Question 17

Reductive wines often form hydrogen sulfide (smell of rotten eggs), add what to reduce the problem?

Answer 17

tiny quantities of copper sulfate

Question 18

Due to the high levels of alcohol and acidity the only microorganisms that can survive in a wine are? (3)

Answer 18

1. lactic bacteria
2. acetic bacteria
3. Yeast

Question 19

only a few microorganisms can survive in wine but where can also wine be tainted by moulds?

Answer 19

poorly-cleaned winery surfaces, particularly inside barrels.

Question 20

Name some of the factors that affect the growth of the microorganisms in wine? (8)

Answer 20

1. pH, the lower the bigger problems for organisms to survive.
   2 Alcohol, kill most stuff if over 15%
2. temperature, growth is fastest between 20-35°
3. Sulfur dioxide, 20mg/l free SO2 will prevent the growth of most of them.
4. residual sugar, presence of sugar is allways a risk.
5. Growth factors, nutrients present will aid spoilage.
6. Air (oxygen), is essential for the growth of acetic bacteria
7. Winery hygiene, good hygiene minimise risk.

Question 21

Lactic bacteria carry out what, if unwanted how do you prevent?

Answer 21

Malolactic fermentation, 20 mg/l of free sulfur dioxid with clarification (removal of nutrients sources en reduction of the population levels of lactic bacteria) and good winery hygiene.

Question 22

If MLF happens in bottle, to a wine with low acidity what happens? and if the wine also has low sulfur dioxide?

Answer 22

lactic bacteria break down tartaric acid, not good.

If low SO2, lactic bacteria will give a slimy and ropy textur.

Question 23

Why is Acetic acid bacteria so difficult to prevent?

Answer 23

its naturally well adapted to grow in sugar-rich and alcohol-rich environments.

Question 24

What is it that Acetic acid does in the wine?

Answer 24

convert alcohol to acetic acid (vinegar), also formed combines with alcohol to form ethyl acetat witch is the smell of acetone (nail polish remover).

Question 25

What is the only way to prevent acetic acid spoilage?

Answer 25

its aerobic, keep minimum contact with air, free sulfur of 20 mg/l and good winery hygiene.

Question 26

What is the only way to prevent yeast growth (yeast spoilage) in wine?

Answer 26

sterile filtration at botteling.

Question 27

What is Candida?

Answer 27

Surface film spoilage yeast, a floor yeast (not sherry yeast!!)

Question 28

Surface film spoilage yeast produce what in the wine?

Answer 28

Acetaldehyde, (ethanal) creating a yeasty taint.

Question 29

Saccharomyces cerevisiae is what?

Answer 29

the type of floor that bloom under specific conditions such as the production of sherry or vin jaune.

Question 30

Brettanomyces will produce what in large quantities?

Answer 30

Volatile phenols, like 4-ethyl-phenol (4-EP), 4-ethylguaiacol (4EG).

Question 31

Brettanomyces can give what at high and low levels?

Answer 31

High: farmyard, sticking-plaster flavours
Low: add complexity to the wine.

Question 32

What type of wine is most susceptible to brettanomyces?

Answer 32

New red wines with high pH ( Syrah, and Cabernet Sauvignon) , can but rare in white wines due to lower pH.

Question 33

What are the only effective means of removing brettanomyces in wine?

Answer 33

Sterile filtration and DMDC ( dimethyl dicarbonate) DMDC is permitted for use by the EU since 2007.

Question 34

Re-fermentation due to the presence of yeast in bottle can do what to the wine?

Answer 34

Cloudiness and gasiness in wine, leads to the kork to pop out of the bottle or bottles with screwcaps to explode.

Question 35

Adding what to the wine will help to avoid re-fermentation in bottle and can give what to the wine?

Answer 35

Sorbic acid, can give a strange, rancid flavour. And if lactic acid bacteria metabolise sorbic acid it can create a smell of geraniums.

Question 36

Other chemical instabilities (or casses) may be caused by? (4)

Answer 36

1. protein
2. phenolic compounds
3. copper
4. iron

Question 37

Precipitation of zink, tin, lead or aluminium in wine can cause this rare problem?

Answer 37

Haze in wine.

Question 38

In what type of wine can unstable proteins cause a haze, cloudiness or a deposit, if subjected to hot or cold temperatures or aged for a extended amount of time?

Answer 38

white wine

Question 39

why does not protein haze usually form in red wine?

Answer 39

the phenolic compounds present precipitate out much of the protein early on in the winemaking. deposits can form, usually due to insoluble pigmented tannins or protein.

Question 40

What is the most common way of removal of unstable proteins?

Answer 40

Bentonite fining

Question 41

how is the bentonite fining of unstable proteins done?

Answer 41

fill 10x10 ml test tube with clear wine
add increasing doses of bentonite to each tube, bentonite may need swelling in water for 24 hour before hand.
shake well and leave for a hour or so in room temperature.
centrifuge or filter the wine to remove the bentonite
carry out protein stability test in all the tubes
note the concentration of bentonite and then add to the “real” wine

Question 42

A filtered sample of new wine is kept between 0-4° for 12 hours, if an appearance of haze will form the risk of colour material will come out of solution, forming a deposit. What is described and how do we fix it?

Answer 42

Phenolic stability test, fined by albumen (egg white) or gelatin.

Question 43

Copper in normally present at low levels in new wine, what levels?

Answer 43

0.3 -0.4 mg/l

Question 44

the concentration of copper in new wine may increase during maturation in the winery due to? (2)

Answer 44

1. contact whit equipment made of copper, tin or bronze

2. addition of copper sulfate to eliminate hydrogen sulfites or mercaptans

Question 45

copper is toxic to humans, the maximum permitted copper in wine in the Eu and the Us is?

Answer 45

1 mg/L in Eu

0.5mg/L in Us

Question 46

What can happen in white wines if the concentration of copper is more than 1 mg/l?

Answer 46

Copper casse, a reddish-brown haze and deposit.

Question 47

Copper casse exist in two forms in a wine, what?

Answer 47

the oxidised state - forms soluble compounds and the reduced state - form poory-soluble compounds.

Question 48

if the copper concentration is above 1mg/l the two preventative methods are effective!

Answer 48

1. Bentonite fining, reduces the level of unstable protein.

2. Gum arabicum, protective effect - prevent the flocculation of the colloid.

Question 49

The most effective process for eliminating excess copper is potassium ferrocyanide treatment, also called? What will it do and why need to be used with caution?

Answer 49

Blue fining.
Will form insoluble deposits, removal by filtration.
Is highly toxic, extreme caution!!

Question 50

What are the levels of natural iron in grapes and what is the maximum permitted levels by the EU?

Answer 50

0 -5mg/l

10 mg/l

Question 51

if the natural iron in grapes are over the expected levels, what may have happen? (2)

Answer 51

contamination of harvested grapes by high iron level is soil.
contact with mild steel or cast iron containers or crusher rollers

Question 52

As with excess copper, excess iron is mostly a problem associated with ____ wine making and unstable iron will form a?

Answer 52

White winemaking, a haze followed by a white deposit (iron phosphate).

Question 53

As with copper iron can exist in two form, what?

Answer 53

a oxidised state (ferric) insoluble compounds

a reduced state (ferrous) soluble compounds

Question 54

Wines showing excess or unstable iron may be treated by? (4)

Answer 54

1. citric acid, combines with iron to form iron citrate, which is very soluble (max amount in EU is 1 mg/l not always sufficient)
2. gum arabicum, stop the precipitation of ferric colloid.
3. Ascorbic acid (vitamin C) , prevent oxidation.
4. potassium ferrocyanid for white and calcium pyhtate for red wines.