Key points on MLF Flashcards
11 factors contributing to MLF
- pH (most important)
- S02
- Nutrient Composition
- Oxygen
- CO2
- Alcohol
- Temperature
- Organic Acids
- Phenolics or phenolic acids
- Presence of other LAB
- Bacteriophage
MLF inhibited by (7)
- Use of SO2 (should be used after)
- Early racking (it likes solids)
- Downward pH adjustment
- Low temp
- Filtration/Fining
- Addition of Fumaric acid (only outside EU)
- Bacteriocin (lysozyme) addition (egg whites and are the best additive to prevent MLF)
How to inhibit MLF (4)
- Add SO2
- 0.8 mg/L molecular pH adjusted - Temperature
- Below 18°C and as low as 13°C - High ethanol does not always inhibit because often coupled with high pH
- Acidity
- Adding tartaric acid (better than malic acid) will help but may not stop it
- Wines pH 3.3 and below need to be stimulated while wines greater than 3.3 will be difficult to stop
Inhibition 2 (3)
- Elimination of viable bacteria
- Sterile filtration and sterile bottling
- Chemical inhibitors
Lysozyme
Egg whites that are used as an antimicrobial agent. When we use this we need to avoid adding close to bottling it is a protein and is capable of combining tannins
Importance of Lysozyme
It is included among wine additives able to control fermentation processes and avoid spoilage during wine making. Because it is an animal product its not vegan.
Amount of Lysozyme added
The amount of lysozyme added normally ranges between 25 and 50 g/hL.
Organic acids that can be added (3)
- Fumarate inhibitory at low concentrations
- Fatty acids (C8 and C10 released by yeasts)
can also be inhibitory - Malate stimulates growth prior to malolactic fermentation
Oxygen (3)
- Stimulatory to growth
- Affects spectrum of end products
- Can produce more energy (and acetic acid) in presence of oxygen (TCA cycle, via citrate a/o by pentose phosphate pathway –> Eterof. LAB)
Carbon Dioxide (2)
- Stimulatory to malolatic fermentation
- Mechanism unknown
Bacteriophage
- Bacterial “viruses” that can be spread from one bacterium to another and that cause cell death
- Not known if this is a problem in wine production or not; it is a problem in other lactic acid bacteria fermentations
Presence of Other Lactic Acid Bacteria positive
- Mixed cultures may yield “better” complexity
- Can be stimulatory
- Increase in pH (Difficult to start MLF below 3.3-3.4 pH)
Presence of Other Lactic Acid Bacteria Negative
Can be inhibitory
- Bacteriocin production (Lysozyme)
- Competition for nutrients
Nutrient Composition (4)
- Lactic acid bacteria are fastidious: numerous growth requirements
- Aging on yeast lees increases micronutrient content via autolysis
- Extended skin contact enhances lactic acid bacteria
- Higher solids or a less clarification degree enhance lactic acid bacteria
Remember Red wines have more nutirents because they offer more solids
Yeast and Bacteria interaction (Metabolization)
Yeast and bacteria are competing for nutrients
( Yeast are mainly interested in sugars
and are able to metabolize amino acids)
Yeast and Bacteria interaction (bacteria growth)
Yeast can both inhibit and stimulate bacterial growth
What inhibits bacterial growth
Formation of ethanol, bisulfite and fatty acid by yeast
What else stimulates bacterial growth
SO2 binding and the products of yeast autolysis after “sur lies” aging
Death Phase
Bacteria can stimulate death phase in yeast
Choice of strain of Bacteria and yeast (5)
- compatibility
- Production of desirable characteristics
- Ability to complete MLF
- Vigor
- Availability of freeze dried inoculum
Inoculated MLF (4)
- Better control over both timing and organisms present
- Difficult to maintain inocula
- Starter culture must be “pure”
- Percent inoculation: 1-50% depending upon vigor of culture
Inoculum prep (4)
- Start culture from a medium supporting good growth of organism
- Inoculate “diluted” juice (with water) with starter and addition of nutrients
- Use #2 to inoculate full strength wine or juice with addition of nutrients
- Use #3 to inoculate the rest of wine
Spontaneous MLF (3)
- Uncontrolled timing of process
- Risk of unwanted species/strains
- Off-characters can be produced if MLF when undesired
Timing of MLF (4 options)
- Prior to yeast fermentation
- Simultaneous with yeast fermentation
- Mid-way through yeast fermentation
- After yeast fermentation
Pre Ferm Inoculum (2)
- Decreases yeast nutrients
- Stuck/sluggish fermentation
- Production of off-characters - May lead to production of inhibitory compounds (acetic acid) due to presence of oxygen
Simultaneous yeast inoculation (3)
- See increase in acetic acid
- See a decrease in viability of both yeast and bacteria
- Yeast “rebound” better than bacteria
Mid Ferm inoculation (4)
- Nutrients left for bacteria
- Ethanol low and not inhibitory
- Yeast-produced SO2 may be inhibitory
- May lead to arrest of yeast fermentation
Post Ferm Inoculation (4)
- Nutrients have been depleted
- Ethanol concentration high
- Concentration of other yeast inhibitory compounds also high
- Better temperature control
