During alcoholic fermentation the microflora present can utilize macro and micronutrients. This may result in a nutrient-depleted environment for the fastidious O. oeni. From a nutritional standpoint, Oenococcus spp. require amino acids, as they do not have the ability to assimilate ammonium salts. The individual amino acids that the bacteria require vary depending on the strain. Using knock-out studies, it has been observed that some strains require as many as 13 of the 20 amino acids.7 These amino acids are deemed to be essential, and others may be necessary as well. If they are not present, growth cannot occur.

In addition to amino acids, it is essential that wine bacteria are supplied with peptides, vitamins (biotin, thiamine, nicotinic acid, and pantothenic acid), and minerals (manganese, potassium, and magnesium). Since we have no practical means of determining amino acid deficiencies for bacteria, we may not be aware that the bacteria are encountering a nutritionally-depleted environment. We can, however, “guestimate” if we know both the yeast assimilable nitrogen concentration at the beginning of the alcoholic fermentation plus the specific nitrogen requirements of the wine yeast used.

S. cerevisiae are classed as low, medium, medium-high, high, and very high with regards to their nitrogen requirements. The different yeast strains available vary significantly in the amount of nitrogen they need to assimilate 1 g/L of sugar. This amount may vary from 0.5 to 1.35 ppm of available nitrogen, with the ex-S. bayanus strains requiring even more.6

Other lesser known factors can also cause inhibition of bacteria. These include alterations in acidity due to either the utilization of malic acid by yeast (or other bacteria) or by production of succinic acid.4 Production of the aromatic compound ß-phenylethanol (floral) by cryotolerant yeast species can also have a negative effect on the growth of O. oeni.1

speculated that acetic acid alone may not be antagonistic, but when in combination with other metabolites, it can lead to an accelerated death of wine yeast.

Suggested causes of accelerated death include the formation of inhibitory metabolites or depletion of essential nutrients and survival factors that are essential to the wine yeast. Other bacterial inhibitors that may have a negative effect on wine yeast include bacterial protease production, extracellular glucanase activity, and bacteriocin- like inhibitors.1

The released mannoproteins have a dual function. They can detoxify the medium and protect the cells from potential polyphenolic inhibition. Mannoproteins may have an additional role in enhancing the nutritional content of the wine. This is possibly due to the glycosidase activity in O. oeni that results in hydrolysis of the mannoprotein. The release of amino acids and peptides can shorten the lag phase of the bacteria and increase the biomass. Yeast autolysis rates are highly strain- and environment-dependent.

To help the winemaker make decisions on yeast/bacteria compatibility, Table II has been developed by Lallemand (adapted for strains available in the North American market).

Based on current knowledge, the success of malolactic fermentation is due to the winemaker’s strain choice(s) for alcoholic and malolactic fermentations, environmental conditions, and winemaking practices employed.

It is recommended that the malolactic fermentation be planned in conjunction with the alcoholic fermentation in order to maintain wine quality and consistency. Table III summarizes the many factors that can play a role in the outcome of malolactic fermentation.

If your wine shows that favorable or mildly difficult conditions exist, a direct bacteria addition can be used. If the conditions indicate that harsher conditions exist, the best approach would be to try a one-step formulation (final acclimatization conducted in your wine). If extreme conditions are apparent, a standard build-up culture would be recommended.