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WSET Diploma: Unit 2 > MTB 1: Post-Fermentation Operations > Flashcards

MTB 1: Post-Fermentation Operations Flashcards

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1
Q

What causes the increase in VA?

A

The gradual oxidisation of aldehydes, producing acetic acid.

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2
Q

Ideal bulk storage temp. for red:

A

Between 10 and 20 degs, ideally 15.

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3
Q

Ideal bulk storage temp. for delicate whites and rosés:

A

Below 10 degs

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4
Q

Optimum humidity level:

A

75-85%

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5
Q

Free SO2 levels needed to stop oxidation:

A

At least 20 mg/L

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6
Q

Define ‘ullage’

A

The amount by which a container falls short of being full.

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7
Q

Inert gases used for blanketing and prevention of spoilage yeast/bacteria:

A

Nitrogen (low solubility, used to sparge wine, removes dissolved oxygen, for reds), carbon dioxide (dense, dissolves well, whites) and argon (pricey).

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8
Q

Benefits of micro-oxygenation:

A

Reduction of herbaceous aromas, better structure, better oak integration, control of reduction.

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9
Q

Why do oxidatively aged wines become more concentrated?

A

Because of evaporation.

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10
Q

In biological ageing, ethanal degrades resulting in…

A

Diethyl acetyl

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11
Q

Lees encourage…

A

MLF - providing nutrients.

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12
Q

Too thick or unstirred lees can lead to…

A

Hydrogen sulphide or mercaptan odours.

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13
Q

Effects of small barrels (less than 500 litres):

A

Reduction of fresh aroma, early tannin polymerisation, stabilisation and clarification.

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14
Q

Two kinds of oak:

A

Red (not porous, no good for winemaking) and white (used for winemaking).

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15
Q

Quercus alba:

A

American, low phenols, high aromatics - oak lactone (coconut).

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16
Q

Quercus petraea (/sessiliflora):

A

European, tighter grained, less tannin, highly aromatic - eugenol (cloves), phenol aldehydes - vanillin (oak/vanilla).

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17
Q

Quercus robur:

A

Pendunculate (bearing a stalk with a flower/fruit), not particularly aromatic, but highly extractable polyphenols.

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18
Q

Typical barrel costs (225l barrique):

A

French: €600-€800, American €440.

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19
Q

Key oak origins (France):

A

Tronçais, Allier, Nièvre (central, v. tight grain), Vosges (NE) and Limousin (east of Cognac, tighter and tannic wood).

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20
Q

Oak origins (rest of Europe):

A

Russian, Hungarian, Slavonian (Italy) and Portuguese - cheaper.

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21
Q

Oak origins (USA):

A

Oregon, Minnesota and Wisconsin.

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22
Q

Cutting oak:

A

Sawing vs. splitting. European split along grain to avoid leakage. American can be sawn to maximise yield.

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23
Q

Drying oak:

A

Air vs. kiln. Air-drying leaves less tannic wine. French oak usually left in air for 18-36 months.

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24
Q

Toasting:

A

Degrades wood structure, leaves aromatic compounds. Less toast: tannins and wood notes. More toast: toasty and spicy. Lack of seasoning can make wine sappy/astringent.

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25
Q

Fuder size:

A

1000L

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26
Q

Hoghead size:

A

300L

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27
Q

Puncheon size:

A

500L

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28
Q

Shaving and re-charring:

A

Can add on 10 years more life, but leaves them more brittle and flavours rarely as subtle/well-integrated.

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29
Q

Adding oak chips:

A

Most effective when added during fermentation.

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30
Q

Adding oak staves:

A

During fermentation or maturation.

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31
Q

Toasted oak powder:

A

Illegal in EU.

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32
Q

Extended storage in stainless steel can lead to…

A

Development of hydrogen sulphide aromas. Less of an issue with cement.

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33
Q

Fibre-glass or resin tanks:

A

Cheaper and easier to clean.

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34
Q

Time of blending:

A

Can be done at any point between fermentation and bottling. Should be done before final clarification/stabilisation, as can make product unstable.

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35
Q

Colloids:

A

Large organic molecules, but too small to be removed by filtration alone. Tough to remove by sedimentation.

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36
Q

Clarification methods:

A

Sedimentation and racking, fining, filtration, centrifugation and flotation.

37
Q

Sedimentation:

A

Common for reds, gentle, natural and minimal equipment. BUT, slow and produces lots of lees (usually racked right after fermentation).

38
Q

Racking:

A

Whites in tanks: every 2 months. Reds in barrels: every 3-4 months. Allows monitoring of SO2 levels.

39
Q

Centrifugation:

A

Helps stabilisation (tartrate precipitation), clarifies, quick and removes big particles. BUT, noisy, pricey and can allow oxidation.

40
Q

Organoleptic properties:

A

That which produces an effect on the sensory organs.

41
Q

Fining agents:

A

Electro-statically charged, meaning they attract oppositely charged molecules to clump them together.

42
Q

Bentonite:

A

Form of clay, swells in water and is negatively charged. Removes proteins (enzymes, amino acids and vitamins). Better microbial/heat stability and makes lees settle better.

43
Q

Gelatin:

A

Reduces bitterness and astringency, but reduces body. Best temp. for use is 16-25 degs. Can remove colouring matter and can cause over-fining.

44
Q

Casein:

A

Main milk protein. Used for wines with excess colour, oxidative taints and excess iron.

45
Q

Isinglass:

A

Used to regulate phenolics. Can leave fishy aroma (from fish bladders).

46
Q

PVPP (polyvinylpolypyrrolidone):

A

Synthetic, reduces phenolics and bitterness, stops browning.

47
Q

Carbon/charcoal:

A

Reduces colour/off odours - used with ascorbic acid.

48
Q

Silica sol:

A

Reduces proteins.

49
Q

Tannins:

A

Treats and prevents over-fining.

50
Q

Egg albumen:

A

Most common in fining of reds for harsh/green tannins. 3-8 egg whites needed per 225L barrel.

51
Q

Fining trials:

A
  1. Various agents. 2. Most effective agent at a range of doses.
52
Q

Time of fining:

A

Usually after end of fermentation.

53
Q

Substances which clog filters easily:

A

Polysaccharides, lees of certain fining agents (bentonite). Bacteria clog more than yeasts.

54
Q

Filter rating:

A

Nominally rated: average pore size. Absolutely rated: maximum pore size.

55
Q

Depth filtration (adsorption):

A

Relies on electrostatic and adhesion forces. Thick layered material/DE/cellulose fibres.

56
Q

Earth filtration:

A
  1. Pre-coating of earth on screen. 2. Filtration - earth mixed into wine and passed through. Can have rotary drum vacuum filters (RDVFs).
57
Q

Diatomaceous earth/Kieselguhr and perlite:

A

DE: made of sedimentary rock with diatom (algae) skeletons. Perlite: originally volcanic rock. Better for musts and cloudy wines as it’s coarser.

58
Q

Sheet/pad filters:

A

Pricey, can leave papery taste if citric acid solution treatment not done.

59
Q

Pros and cons of depth filtration:

A

Can deal with high solids content, simple operation. BUT, needs controlling and is not absolute.

60
Q

Surface filtration:

A

Uniform pore size. 0.65, 0.45 and 0.2 micron diameters common. 0.45 will remove ALL yeast and bacteria.

61
Q

Membrane filtration:

A

Thin, flexible material used. Can be washed and reused. Used to sterilise wine just before bottling.

62
Q

Cross-flow membrane filters:

A

Even the dirtiest wines filtered. Liquid passes in parallel, avoiding clogging. Expensive though!

63
Q

Reverse osmosis (RO):

A

Like cross-flow, has highly selective membrane. Counteracts force of osmosis. Concentrates must, de-alcoholises finished wines and reduce acetic acid. Pricey!

64
Q

Osmotic distillation:

A

Produces grape-based concentrates. Uses PTFE/Teflon and brine.

65
Q

Three main causes of instability:

A

Tartrate instability, oxidation and microbial spoilage.

66
Q

Potassium bitrate:

A

The mono-salt of tartaric acid, less soluble. Forms crystals.

67
Q

Cold stabilisation:

A

Chilling wine to between -4 and -8 degs., then racking. Less common now.

68
Q

Contact process:

A

Chilling wine to 0 degs. with heat exchanger. Powdered potassium bitartrate crystals applied. Encourages further growth. Crystals removed, dried and whole thing repeated.

69
Q

Gum arabic:

A

Kind of protective colloid which stops crystals growing to become too large. Short effects though. Only for wines for quick consumption. 50-200mg/L.

70
Q

Metatartaric acid:

A

Stops crystal growth, short-lived. Does better at cooler temps. 100mg/L.

71
Q

Calcium tartrate:

A

Forms very slowly. Can be solved by ion exchange/electro-dialysis.

72
Q

Ion exchange:

A

Not allowed in EU. Passing wine though resin with sodium ions. Can leave high sodium levels, so banned.

73
Q

Preventing oxidation:

A

Free SO2 should be at a minimum of 20mg/L.

74
Q

Use of ascorbic acid without SO2 can lead to…

A

Oxidation

75
Q

Treating laccase activity:

A

Pasteurisation

76
Q

Removing hydrogen sulphide from wine:

A

Aeration or addition of very small amounts of copper sulphate.

77
Q

Only microorganisms capable of surviving in wine:

A

Lactic bacteria, acetic bacteria and yeast.

78
Q

MLF in bottle:

A

Clouds wine and leaves unpleasant smells.

79
Q

Acetic acid bacteria:

A

Convert ethanol to acetic acid (vinegar). Acetic acid combine with alcohol to make ethyl acetate (smells of acetone/nail polish remover).

80
Q

Lactic acid bacteria:

A

Can break down tartaric acid and make wine ropy or slimy.

81
Q

Preventing formation of spoilage yeasts:

A

Sterile filtration.

82
Q

Surface ‘film’ spoilage yeasts:

A

E.g. Candida - grow on surface of wine in contact with air. Causes bloom/flor. NOT THE SAME as one used in Sherry/Vin Jaune. These oxidise ethanol to make acetaldehyde (yeasty taint).

83
Q

Brettanomyces:

A

Produces volatile phenols - farmyard, sticking plaster. High-pH Syrah and Cab Sauv are most susceptible. Rare in whites as they have lower pH. Often lives in wood. SO2 can help. Removed by sterile filtration and DMDC (dimethyl dicarbonate).

84
Q

Sorbic acid (avoiding re-fermentation in bottle):

A

Can cause stoppers to pop out, leave cloudiness and gasiness. Sterile filtration before bottling needed. Sorbic acid can minimise risk. Antimicrobial agent added at bottling at 100-200mg/L. Can be detected - rancid flavour. Lactic acid can metabolise - geraniums! Quite rare.

85
Q

Protein instability:

A

Haze, cloudiness or deposit. Water bath test, looks milky. Bentonite must be used sparingly.

86
Q

Phenolic instability:

A

Albumen and gelatin used. Shouldn’t throw too much deposit too early.

87
Q

Excess copper:

A

Normal levels: 0.3-0.4 mg/L. Copper sulphate and equipment can increase it. Max in EU is 1mg/L and 0.5mg/L in USA. Monitored by gas chromatography. Not detectable straight away. Bentonite fining and gum arabic needed. Blue fining/potassium ferrocyanide - but toxic!

88
Q

Excess iron:

A

Unstable over 6mg/L. EU max is 10mg/L. Close observation needed with gas chromatography. More in whites, leaves cloudy iron phosphate haze/deposit. Soon after bottling. Ascorbic acid, gum arabic, citric acid or potassium ferrocyanide (whites) and calcium phytate (reds).

WSET Diploma: Unit 2 (8 decks)

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