Bacteria and wine acidity Fundamentals

Question 1

Reasons MLF is desirable (5)

Answer 1

1. Acidity Reduction
2. pH increase
3. Importation for high acid wines
4. Addition of flavors
5. Biological stability of final product

Question 2

Reasons MLF is undesirable (2)

Answer 2

Acidity reduction and addition of flavors

Question 3

MLF modifies flavor profile (3)

Answer 3

1. Less sour
2. Butter aromas
3. Aroma change more evident in white wines than red wines

Question 4

Flavor changes associated from MLF (components)

Answer 4

Acetic acid and Diacetyl

Question 5

Acetic Acid origins (3)

Answer 5

1. From sugar metabolism
2. From citrate metabolism
3. low levels from Saccharomyces

Question 6

Diacetyl (5)

Answer 6

1. Made from pyruvate
2. 1-4 mg/L adds complexity (butter)
3. Over 4 mg/L dominates
4. Low amounts can be produced by yeast
5. Many pathways to get Diacetyl

Question 7

Another compound that can be produced by lactic acid

Answer 7

Acetoin: can be produced from pyruvate as well as Diacetyl, usually below the threshold in most wines

Question 8

What is derived from Acetoin

Answer 8

2,3 Butantediol: usually below threshold, can produce mild alco flavor that resembles bitterness, can also be produced by yeast

Question 9

Wine spoilage by LAB

Answer 9

Lactic Acid Bacteria
1. A less serious form of lactic spoilage can occur in dry wines.
2. Degradation of Glycerol
3. Fermentation of Tartaric Acid.
4. Fermentation of Citric Acid
5. Ropiness
6. Other off aromas (mousy flavor)

Question 10

Monitoring MLF

Answer 10

1. By conversion of malate to lactate
   - Loss of malate not appearance of lactate*
2. By flavor changes
   - Tells you bacteria are active

Question 11

Amino acids can form what?

Answer 11

Amino acids can for biogenic amines via a loss of CO2