The whole process involving yeast and alcoholic fermentation (AF) has been greatly studied and, as a result, is largely understood. This is not the case yet with lactic acid bacteria and malolactic fermentation (MLF). The effect of MLF not only on wine quality and microbial stability but also on the aroma profile of a wine is greatly underestimated and, in many cases, ignored or misunderstood. For these very reasons, as well as from a cost-saving perspective, many winemakers prefer to leave this process to be performed by indigenous lactic acid bacteria (LAB).
Malolactic fermentation, also called Malo or MLF, is a microbial process that occurs after alcoholic fermentation in winemaking. It is the conversion of harsh-tasting malic acid to softer-tasting lactic acid by lactic acid bacteria (LAB), which results in decreased acidity and changes to the aroma profile of the wine.
Previously isolated and described in 1960 as Leuconostoc oenos, this bacteria is now better known as Oenococcus oeni. Besides decreased acidity and microbial stability, the most often overlooked effect is that of the bacteria on the final wine aroma profile. The indigenous microbial population of must and/or wine is very complex, with the LAB responsible for the conversion of malic acid to lactic acid.
In wine, species from Oenococcus, Lactobacillus, and Pediococcus could potentially play a role in MLF.
The strains all differ in their tolerance to pH, alcohol, sulphur, temperature, and nutrient demand.
Malolactic fermentation can take place without inoculation (spontaneously) or as a result of the addition of a commercial preparation of lactic acid bacteria (starter culture) to the juice (co-inoculation) or wine after alcoholic fermentation. (sequential inoculation)
Whether the bacteria present result in the onset of MLF is dependent on the initial bacteria concentration; at least 1 x 106 CFU/mL is required. Concomitantly, the growth and survival of the bacteria are dependent on a variety of other factors.
Due to the fact that there are so many influencing factors, spontaneous MLF holds countless risks and is very unpredictable. This includes unpredictability when it comes to timing (onset and completion), as well as uncertainty as to what exactly is performing the fermentation (spoilage bacteria). The natural microflora population will also be dependent on cellar hygiene practices.
Risks involved with spontaneous MLF include the following:
If you do not inoculate for MLF with a commercial starter culture and your indigenous bacteria population is insufficient, you may have to wait for months, and in some cases, until the following spring, to have MLF completed. The delay between the completion of AF and the onset of MLF presents a huge risk for the development of Brettanomyces, as conditions remain favourable for the development of this spoilage yeast (high temperatures, low SO2 concentrations, and nutrients). Winemakers also have to prevent the risk of MLF taking place in the bottle.
Factors that are important to consider when choosing a LAB strain(s) for MLF inoculation include, among others:
In comparison, the advantages of MLF with an inoculated bacterial starter culture are:
Inoculated MLF also has the added benefit of inoculating the bacteria at a higher inoculum concentration compared to the indigenous LAB population generally present. This has been shown to result in faster MLF, reduced buttery characteristics, and reduced off-flavours.
All our culture bacteria are produced for direct seeding, which means the bacterial population is pre-acclimatised to the wine’s conditions. This results in a relatively easy addition, in which the preparation is poured into 20 times its weight of mineral water before being incorporated into the wine from the top of the tank and homogenised by pumping over.
Malolactic fermentation (MLF) must be managed well to achieve wine’s organoleptic qualities. Controlling numerous major oenological characteristics is necessary for this procedure, which might change wine aroma, taste, and stability:
With a highly qualified team of experts in many fields, Oenobrands strives to offer winemakers’ novel and scientifically sound solutions, as well as to highlight the positive synergies between its products.
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