This protocol is efficient when wines parameters are not outside of known limiting conditions (high SO2 content, high alcohol content, low pH, possible excessive amount of pesticides residues, possible presence Chitosan in certain conditions).

Potential causes for incomplete  malolactic fermentation (MLF)

Inappropriate use of bacteria

The choice of the selected bacteria, timing of inoculation, and respect of the instructions of use (dosage, rehydration temperature) and storage conditions are keys to insure a good success of MLF.

SO2 Levels

Free SO2 will inhibit bacteria growth and MLF completion even at low levels, its impact is even stronger at low pH. But total SO2, when higher than 50ppm can have a negative impact on bacteria vitality: in this case selected bacteria with higher total SO2 tolerance have to be chosen.

pH

Every selected wine bacteria have its specific limits with regard to pH. If the wine pH is lower than the pH limit of the selected bacteria, MLF may not proceed. In the case of wine pH lower than 3.5 the bacteria tends to require more nutrients to perform MLF accordingly.

Nutrient limitation

This is considered to be one of the major causes of incomplete MLF. Lactic acid bacteria have specific needs for peptides and amino acids which have to be satisfied in order to achieve an optimal growth and metabolism to perform malolactic fermentation and especially under limiting conditions.

Other inhibiting compounds

• Certain phenolic compounds can inhibit MLF such as certain condensed tannins whereas

others such as anthocyanins can stimulate them.

• Pesticides residues are known to cause sluggish, stuck or complete inhibition of MLF

• The presence of high L- lactic acid content (in case of high initial level of malic acid) can inhibit

the good achievement of MLF if the right resistant selected bacteria are not used.

• The treatment with new solutions like chitosan or chitines derivates can disturb the good start

or full achievement of MLF depending on wine conditions and on the treatment timing.

• Some yeast strains, especially when they have struggled to complete alcoholic fermentation,

can release toxic metabolites which cause MLF issues.

• Medium-chain unsaturated fatty acids can also have a negative impact on bacteria growth

and activity.

Ethanol content

As for all microorganisms ethanol can have a strong toxicity especially at high temperature.

It’s key to choose the appropriate bacteria which can tolerate the respective ethanol content of

the wine.

Temperature

Optimal temperature for MLF is between 18 and 22°C. Some bacteria differ in their tolerances for

lower temperatures and it’s usually better to avoid higher temperatures in the case of low pH

wines, wines with high ethanol or SO2 content.