Chapter 7

Malolactic Fermentation in Wine

Environmental Conditions Affecting Bacterial Growth

The environmental conditions affecting bacterial growth, include temperature, pH, concentrations of sulfur dioxide, and alcohol, play a role in the successful course of malolactic fermentation (Table 7.2). Other compositional parameters such as yeast/bacteria compatibility, nutrition, and pesticide residues from the vineyards also play a role in the development of the lactic acid bacteria.

Alcohol

Alcohol can impair the ability of Oenococcus oeni to conduct fermentation and is inhibited by alcohol concentrations above 6 percent, with 14.5 percent v/v the upper limit tolerated by most malolactic bacteria (Morenzoni et al., 2015).

Fatty Acids

If the yeast are under nutrient or environmental stress during alcoholic fermentation, they excrete short- to medium-chain fatty acids (octanoic and decanoic acids) which inhibit both yeast and bacterial function (Bowyer et al., 2010).

Lees Compaction

Lees found at the bottom of a tank can become compacted due to hydrostatic pressure, resulting in yeast, bacteria and nutrients being confined to the point that they cannot function properly. Larger tank sizes may contribute to increased delays in the start of malolactic fermentation.

Lysozyme Activity

If lysozyme is used to control indigenous lactic acid bacteria (Pediococcus and Lactobacillus spp.) during the production of wine or postpone the malolactic fermentation, it is possible that residual levels of this enzyme may impact the duration of the subsequent malolactic fermentation (Section 18.7).

Nutrient Deficiencies

Lactic acid bacteria have complex nutritional needs, requiring the presence of carbohydrates, amino acids, peptides, fatty acid esters, salts, nucleic acid derivatives, and vitamins. Diammonium phosphate is of no benefit to bacteria since they cannot use inorganic nitrogen. Yeasts usually consume the most wine essential nutrients during the alcoholic fermentation.

Pesticide Residues

Certain pesticides may have a detrimental effect on lactic acid bacteria.

pH

pH is probably the factor with the greatest influence on the development and fate of LAB in wine. Depending on several factors, such as the grape variety, climate, and ripeness, the minimum pH of wine before malolactic fermentation ranges from 3.2 to 3.5.

Sulfur Dioxide

Oenococcus oeni is more sensitive to the antimicrobial effects of sulfur dioxide than are other lactic acid bacteria. Lactic acid bacteria are much more sensitive to sulfur dioxide than yeasts. Consequently, nominal additions of sulfur dioxide should be used as little as possible, or not at all, where the malolactic fermentation is desired.

Tannins

Some red grape varieties may have difficulty completing a successful malolactic fermentation such as Merlot, Tannat, and Zinfandel (Kelly, 2018).

Temperature

Although the optimum growth temperature for lactic acid bacteria is around 30 degrees C (86°F), as the alcohol concentration increases the optimum temperature falls sharply due to the increased toxic effects of alcohol on bacteria at higher temperatures.

Yeast/Bacteria Compatibility

The interaction between bacteria and yeast during alcoholic fermentation and/or malolactic fermentation will have a direct effect on lactic acid bacteria growth and malolactic activity. For example, under specific conditions, certain yeast strains may produce high concentrations of sulfur dioxide which has a negative influence on the growth and survival of the malolactic bacteria.

Yeast Strains

The selection and characterization of strains for possible use in a commercial culture is crucial, due to the fact that lactic acid bacteria strains differ in their fermentation capabilities and growth characteristics. Some of the characteristics include the following: tolerance to low pH, high alcohol and sulfur dioxide concentrations, good growth characteristics under winemaking conditions, compatibility with Saccharomyces cerevisiae, ability to survive the production process, the inability to produce biogenic amines, the lack of off-flavor or off-odor production as well as the production of aroma compounds that could potentially contribute to a favorable wine aroma profile.

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