Wine pH and Acidity

Question 1

Four types of organic acids found in wines

Answer 1

1. Diprotic acids
2. Monoproptic
3. Triproptic
4. Acids that are products of fermentation

Question 2

Monoproptic Acids

Answer 2

Acetic and Lactic

Question 3

Diproptic Acids

Answer 3

Tartaric, Malic, and Succinic

Question 4

Triproptic Acids

Answer 4

Citric

Question 5

Acids that are products of alcoholic Fermentation

Answer 5

Acetic and succinic and lactic

Question 6

3 effects of pH on Wine

Answer 6

1. biological stability – spoilage organisms are generally inhibited at lower pH, whereas high pH may favour them
2. colour - particularly of reds, lower pH wines exhibit more purple and ruby tones, higher pH wines more brick and orange tones
3. oxidation rate – increased at higher pH

Question 7

3 more effects of pH on Wine

Answer 7

1. overall palatability is affected by wine pH
2. effectiveness of preservatives (SO2) – the active (molecular)
   forms of sulphites exist at higher levels at lower pH
3. tartrate stability – dissociation of tartaric acid is pH dependent

Question 8

Tartrate Stability VS. Wine pH

Answer 8

There is a Linear correlation between high pH and high tartrate stability.

Question 9

What is pH

Answer 9

The fraction of protons released by acids

Question 10

pH versus Titratable Acidity

Answer 10

1. pH is a measure of [H+] only
2. pH in wine depends on both the concentration of acids present and their relative degrees of dissociation
3. Titratable acidity measures free [H+] plus all undissociated acids that can be neutralised by a base
4. pH and TA are not the same thing, nor do they have a linear relationship!

Question 11

Wine is a chemical buffer system (3 things)

Answer 11

1. A buffer solution resists changes to pH when addition of acid or base is made
2. Buffer solutions consist of a weak acid and its conjugate base (or vice versa) in chemical equilibrium
3. The buffer capacity of wine is a result of the combined effects of different organic acids in both their dissociated and salt forms

Question 12

Mechanism of wine buffer chemistry

Answer 12

1. Simple buffer equilibrium (weak acid buffer) HA =H+ + A-
2. Upon addition of acid, free H+ consumed by A-:
   A- + H+ = HA
3. Upon addition of base, OH- reacts with H+ to produce water: OH- + H+ = H2O

Question 13

Wine pH and acidity (2 things)

Answer 13

1. Equilibrium chemistry of wine acids and salts is modified by presence of alcohol
2. Solubility of some species is lower in alcoholic solution, particularly tartrate salts

Question 14

5 Consequences for Winemaking

Answer 14

1. Difficult to significantly alter high pH levels in juice or wine by acid additions
2. Winemakers must judge effect on pH against effect on flavour and wine balance
3. Buffer capacity of individual wines will vary depending on their organic acid profile
4. Cannot easily predict the effect on pH of a given acid addition
5. Only slight changes in pH during normal fermentation

Question 15

Wine acidification

Answer 15

Wine acidification may be carried out up to an increase in titratable acidity of 2,50 g/L as tartaric acid. (only organic acids can be used)

Question 16

Deacidification

Answer 16

Only wine can be deacidified up to a maximum reduction of 1 g/L.

Question 17

Deacidification and KHT

Answer 17

When we loose KHT the pH increases because we loose some protons from KHT. Alcoholic fermentation is a natural deacidification.

Question 18

Acidification Treatment

Answer 18

all the acid that is added will precipitate after cold stability under the form of KHT.