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Advances in Enology > Controlling Protein Stability (Clearing haze) > Flashcards

Controlling Protein Stability (Clearing haze) Flashcards

1
Q

What is Chitinases

A

An enzyme that breaks down chitin (a polysaccharide) but is a protein

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2
Q

What is unfolding

A

Unfolding is the process of the proteins unfolding leading to flocculation and precipitation.

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3
Q

What is flocculation?

A

a process by which colloidal particles come out of suspension to sediment under the form of floc or flake, either spontaneously or due to the addition of a clarifying agent.

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4
Q

Role of sulfur in protein stability

A

Disulphide bonds are important because they are a direct bond between two sulfur compounds. This can lead to protein that is more closed and folded due to the strong bond.

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5
Q

Isoelectric point

A

“iso” means the same, so when the discussing molecules, it can mean that they have the same charge. The charge is at zero when at the isoelectric point (same number of negative and positive charges.

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6
Q

3 instances when proteins are more stable

A
  1. With more disulphide bonds
  2. Within their optimal temperature ranges
  3. In conditions close to their isoelectric point
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7
Q

What is the isoelectic point range

A

4.5-7 pH

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8
Q

For protein stability do we want higher or lower pH

A

Lower pH is less stable for proteins so we want a higher pH

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9
Q

Temperature and protein stability

A

Lower temperatures are more stable

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10
Q

Which proteins are more and less heat resistant?

A

Chitinases and TLP are less heat resistant and LTP and invertases are more heat resistant

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11
Q

2 key things to remember with pH

A
  1. Melt temperature increases with pH
  2. Proteins are more stable at higher pH
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12
Q

What is ionic strength?

A

Minerality of the wine

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13
Q

Protein aggravation is driven by 2 things…

A
  1. Hydrophobic interactions
  2. Electrostatic interactions
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14
Q

More proteins =

A

usually more haze

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15
Q

Polysaccharides in regard to protein aggravation

A

They are always positive and favorable for stabilization
and
They contribute to maintain more hydrated and sulphated compounds

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16
Q

Protein unfolding is influenced by (2)

A
  1. protein composition
  2. storage conditions
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17
Q

Protein unfolding is promoted by (3)

A
  1. Higher temperature
  2. Lower pH
  3. Surface charge changes
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18
Q

Protein Aggregates are influenced by (2)

A
  1. Wine matrix components
  2. Storage conditions
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19
Q

Protein Aggregates are promoted by (2)

A
  1. More Chitinases, ions, acidity, phenolics, SO2
  2. Less polysaccharides, ethanol
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20
Q

Haze forming proteins (2)
and what they can depend on (2)

A
  1. Always present in grape skins
  2. Always considered PR proteins
  3. Viticultural factors
  4. Winemaking factors
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21
Q

Grape varieties that are more/less stable

A

High stability: Chard, Riesling, Glera
Medium: Pinot Grigio, sylvaner
Low stability: SB, Muscat, Gewurtz, Semillon

Aroma precursors are antimicrobial and we find more PRP in grapes with more aroma precursors

22
Q

When does PRP formation start in the grape

A

Veraison

23
Q

Is PRP more or less accumulated in stressed grapes

A

More accumulated (except for botrytis)

24
Q

Water stress

A

Causes smaller berries and more PRP

25
Q

Harvesting and formation of PRP

A

Hand picked grapes usually have less PRP than mechanized

26
Q

Grape skin contact of formation of PRP

A

No maceration and free run juice will have less PRP than extended maceration and heavy pressing

27
Q

How do fermentation conditions affect PRP

A

The longer ferm occurs the more the PRP decreases however it decreases more with lower pH and decreases even more with lower pH and higher ferm temperatures

Less than 50% decrease in protein with fermentation

28
Q

Bentonite fining and PRP

A

Bentonite greatly reduces PRP

29
Q

How can we check to see if there will be haze in the wine

A

Heat test. Heat the wine, then cool the wine and then measure

30
Q

Trends with heat and heat test

A

Haze increases with heating time during the heat test

31
Q

When does hazing actually occur

A

Hazing occurs during the cooling, and it increases with cooler temperatures

32
Q

Critical threshold in wine

A

100mg/L of PRP

33
Q

New Method heat test

A

Heat to 80 Degrees C for 2 hours, cool to 20 degrees C for 3 hours, there is no equilibrium time and total turnaround time is only 5 hours compared to 24 with the original method and 20 with the revised

34
Q

What do we measure with the heat test

A

Turbidity. If the change in Turbidity is less than 2 NTU we have a protein stable wine

35
Q

Does more haze = more bentonite

A

NO

36
Q

Does more protein mean more bentonite?

A

Sometimes

37
Q

Does the heat test predict real world haze

A

It way over compensates and predicts more than actual

38
Q

Bentonite pros (5)

A
  1. Cheap
  2. Readily available
  3. Easy to use
  4. Non-toxic
  5. Effective
39
Q

4 mechanisms of bentonite action

A
  1. Have a net negative charge
  2. Contains positive ions e.g. sodium or calcium
  3. Protein binds to bentonite and displaces smaller ions
  4. Proteins precipitate as bentonite lees
40
Q

3 cons of Bentonite

A
  1. Wine lost as bentonite lees
  2. Non-selective: can remove aroma compounds
  3. Extra processing steps
41
Q

How to reduce bentonite use?

A

Choose the right type of bentonite: different bentonites have different protein absorbing capacities.

Three things to consider:
1. Settling time
2. Dose
3. Lees Volume

42
Q

Sodium based bentonite vs Calcium based

A

Na: Cheaper, use less, produces more lees
Ca: Less lees, use more, may promote tartrate instability

43
Q

What can adding too much bentonite result in

A

It can result in pigment stripping (strip phenolics)

44
Q

1 recycled alternative to bentonite

A

GSP Grape seed proteins. Grape seeds are roasted at 180 degrees C for 10 mins

45
Q

Which bentonite is more reliable for clarifying the must

A

Calcium. There is a risk of calcium instability. Protein stability increases with Ca bentonite

46
Q

Should we do one large dose of bentonite

A

NO. Its best to do a small dose of Ca bentonite for clarification after ferm, then some Na bentonite for fining

47
Q

Role of GSP

A

For fining. It is able to remove chitinases. It very slightly changes the sugar, but can greatly increase the pH

48
Q

Can GSP affect esters?

A

Yes, the seeds are full of fatty acids, which are brought out via ethanol and are then made into esters by yeast .

49
Q

Can we use GSP alone?

A

No, as they are not purified they cannot remove hazing proteins alone, GSP is good to use when you want to use less bentonite

50
Q

GSP benefits (3)

A
  1. can be a viable solution to reduce use of bentonite
  2. should be used with wine not requiring a large amount of fining
  3. May be a good sustainable and economic alternative

Advances in Enology (19 decks)

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