Malolactic fermentation Flashcards
What is malolactic fermentation (MLF)?
The conversion of L-malic acid to L-lactic acid by lactic acid bacteria.
What is the main bacterial species responsible for MLF in wine?
Oenococcus oeni.
What are the effects of MLF on wine?
Increased pH, decreased TA, changes in aroma and taste, potential diacetyl and biogenic amine production.
How does MLF affect wine acidity?
MLF reduces total acidity (TA) and can increase pH by up to 0.3.
What are the key genera of LAB found in wine?
Oenococcus, Lactobacillus, Pediococcus, and Leuconostoc.
Why is O. oeni preferred for MLF?
It is well-adapted to wine, produces fewer spoilage compounds, and contributes to clean MLF.
What is the pKa of malic acid vs lactic acid?
Malic: pKa1 = 3.56, pKa2 = 5.1; Lactic: pKa1 = 3.86.
What are the growth phases of LAB?
Lag, growth (exponential), stationary, and decline phases.
When does MLF typically occur in the bacterial lifecycle?
During the stationary phase.
What factors influence MLF?
pH, SO₂ levels, ethanol concentration, temperature.
What pH conditions favour MLF?
Optimal at pH 3–3.2; inhibited below 3.0.
What SO₂ conditions inhibit MLF?
High molecular SO₂ and total SO₂ inhibit LAB and MLF.
At what ethanol level does LAB inhibition typically start?
Inhibition starts around 5–6%; becomes significant above 13%.
What is the optimal temperature for MLF?
20–25 ºC (minimum ~15 ºC).
What are some other inhibitory factors for MLF?
Polyphenols, C6–C10 fatty acids, bacteriocins, and oxygen.
What spoilage compounds can result from poor MLF?
Diacetyl, biogenic amines, volatile acidity, mousiness, ropiness.
How can diacetyl production be controlled?
By managing SO₂, yeast lees contact, and temperature.
What are some ways to monitor MLF?
Visual/audible cues, organoleptic testing, microscopy, chromatography, enzymatic tests, spectroscopy.
How can MLF be inhibited?
High SO₂, cooling, sterile filtration, lysozyme addition, lees removal.
How can MLF be stimulated?
Co-inoculation, using starter cultures, warming wine, nutrient addition, minimizing SO₂.
