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Malolactic Fermentation Feasibility Evaluation

Last Updated: 5/2022

Applies to: Winemakers looking to prevent stuck malolactic fermentations. This evaluation helps estimate the compounding effect that wine conditions have on MLF.

AVOIDING STUCK MALOLACTIC FERMENTATIONS

The factors that influence malolactic fermentation (MLF) feasibility have compounding effects on one another and cannot be looked at individually. For example, a wine with low pH and high SO2 will be more antagonistic to bacteria than low pH alone. The following scorecard was created to help practically represent this phenomenon.

The scorecard rates how antagonistic several wine conditions are to ML bacteria and returns a total point value representing the predicted difficulty of MLF. Based on this value, Scott Laboratories recommends certain steps be taken to maximize success. This evaluation is most helpful if conducted prior to MLF, but can still be helpful to provide context if a stuck MLF occurs.

ML BACTERIA FEASIBILITY EVALUATION

Use this chart to give a score to your wine for each listed attribute. Add up the point values for each attribute for a total score and evaluate predicted difficulty of fermentation based on the scorecard below.

WINE CONDITIONS1 POINT2 POINTS8 POINTS10 POINTSSCORE

Alcohol (% v/v)

<13

13-15

15-17>17
pH>3.43.1-3.4

2.9-3.1

<2.9
Free SO2 (ppm)<88-1212-15>15
Total SO2 (ppm)<3030-4040-60>60
Temperature64-72°F57-64°F
or
72-75°F
50-57°F
or
75-84°F
<50°F or >84°F
Yeast Nutritional RequirementsLowMediumHighVery High
Ease of Alcoholic FermentationNo problemsTransient yeast stressSluggish or stuck AFProlonged yeast contact
Initial Level of Malic Acid (g/L)2-44-5 or 1-25-7 of 0.5-1>7 and <0.5
Maximum Rate of Alcoholic Fermentation (max. loss of Brix/day)<22-44-6>6
TOTAL SCORE:

Note: Other factors that are currently less well known not considered on the scorecard may include the level of dissolved oxygen content, polyphenolic content, lees compacting, pesticide residue, etc.

TOTAL SCORE:

Use the total score generated from the previous step and consult the table below to

DIFFICULTY OF MLF

Easy

ModerateDifficultExtreme
SCORE

<13

13-2223-40>40
BEST PRACTICESChoose a bacteria strain compatible with the wine conditions and sensory goals.

Ensure temperature is between 14-24°C (57-75°F)
Choose a bacteria strain compatible with the wine conditions and sensory goals.

Conduct MLF at 20°C (68°F).
Choose a bacteria strain compatible with the wine conditions and sensory goals.

Use a malolactic nutrient and conduct MLF at 20°C (68°F).
Consider adjusting wine conditions before inoculating with bacteria. This may include deacidification, reducing alcohol via blending, detoxifying using RESKUE, and warming the temperature to 20°C (68°F).

Consult a technical representative for additional advice.

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Contact a technical representative for assistance with difficult and extremely difficult malolactic fermentations.

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