First, we must understand the causes of a sluggish MLF. The key factors are described in the chapter What conditions influence malolactic fermentation?
The winemaker has several options to stimulate MLF, the primary factor being maintaining a constant temperature.
Another option is to stir the lees in order to detoxify the environment and release the compounds resulting from yeast autolysis. Using yeast autolysate is also a solution.
Reincorporating non-sulphited lees from another batch that has completed its MLF without any problems is also a possibility. Beware, however, of cross-contamination from spoilage organisms such as the Brettanomyces types.
Finally, inoculation with lactic acid bacteria can be used to treat difficult cases. To decide whether or not to inoculate, the presence of lactic acid bacteria can be measured. If the quantity present is already high (more than 105 cells /mL), it means that the multiplication phase has ended and that MLF is about to start. Inoculation would only lead to competition and an even longer latency phase.
However, if the population is low, inoculation is appropriate.