Alcoholic and Malolactic Fermentations

Although species diversity in a must can increase shortly after crush, viable cell number normally remains relatively low ( 10 to 10 CFU/mL) for some period of time (Lonvaud-Funel et al., 1991). Even if inoculated prior to alcoholic fermentation, most lactic acid bacteria experience a rapid die-off during alcoholic fermentation, commonly to populations below lOOCFU/mL. As an example, Edwards et al. (1990) observed the population of O. oeni decrease from 10 CFU/mL to less than 30CFU/mL, resulting in a delayed malolactic fermentation. Sometime after completion of alcoholic fermentation, the population of Oenococcus oeni may increase 

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In this chapter, we reviewed the effect of commonly used herbicides, insecticides, and fungicides on yeasts. We also studied the effect of alcoholic and malolactic fermentation on pesticide residues. 

FIGURE 4.21 H NMR spectra (400 MHz) of time course evolution of red wine in alcoholic and malolactic fermentations for grape red must (pH 3). Peaks 1, ethanol 2, ethanol satellites 3, lactic acid 4, acetic acid 5, succinic acid 6, malic acid 7, 2,3-butanediol 8, proline 9, alanine. (From Avenoza et at, 2006.)... 

Avenoza, A., Busto, J. H., Canal, N., and Peregrina, J. M. (2006). Time course of the evolution of malic and lactic acids in the alcoholic and malolactic fermentation of grape must by quantitative 1H NMR (qHNMR) spectroscopy. J. Agric. Food Chem. 54, 4715-4720. 

At the end of alcoholic and malolactic fermentation, the wine undergoes clarification and stabilization prior to bottling the phase inappropriately called "aging." This is the final step in winemaking, which involved those operations required to permit the expression of features considered necessary to the wine s overall quality. Nuances that distinguish wine styles also develop. 

In particular, aspects requiring further studies include partial dehydration and the consequences of botrytization the development of solution to problems associated with alcoholic and malolactic fermentation and a clear understanding of critical processes associated with maturation. 

Microbial interactions that occur in wine may be beneficial or detrimental to wine quality depending on the species involved. Examples of detrimental interactions are the inhibition of S. cerevisiae by Lactobacillus species and the inhibition of O. oeni by S. cerevisiae when MLF is desired. However, the inhibition of O. oeni may also be beneficial to wine quality if MLF is undesirable. Additional beneficial interactions include the stimulation of LAB growth due to yeast lysis and the inhibition of Pediococcus species by O. oeni. A better understanding of the complex interactions between LAB and S. cerevisiae will lead to the selection of compatible yeast and bacterial strains for the induction of alcoholic and malolactic fermentations. 

Joyeux, A., Lafon-Lafourcade, S., and Ribereau-Gayon, P. 1984b. Metabolism of acetic acid bacteria in grape must. Consequences on alcoholic and malolactic fermentation. Sci. Aliments 4, 247-255. 

Due to their compositiou, musts and wines are acidobasic buffer solutious, i.e. a modification in their chemical composition produces ouly a limited variatiou iu pH. This explains the relatively small variations in the pH of must duriug alcoholic and malolactic fermentation. 

Genisheva Z., Mota A., Mussatto S.I., Oliveira J.M. and Teixeira J.A. Integrated continuous winemaking process involving sequential alcoholic and malolactic fermentations with immobilized cells. Process Biochemistry 49 (1) (2014) 1-9. 

The winemaker s challenge is to optimize those conditions that favor growth of fermentative yeasts (Saccharomyces) resulting in complete alcoholic fermentation (final reducing sugar concentrations of <0.2% w/v) while avoiding formation of undesirable odors or flavors. Ideally, completion of alcoholic and malolactic fermentations should result in a wine that is nutritionally insufficient to support further microbiological activity (i.e., the wine has become a nutrient desert ). 

There has been renewed interest among some winemakers with regard to the use of native microflora present on the fruit and in the winery to carry out alcoholic and malolactic fermentations. Stylistic distinction is the driving force that tempts winemakers to accept the risks involved in these natural fermentations. Perceived benefits include added complexity and intensity as well as a fuller, rounder palate structure. The latter may reflect the presence of small amounts of unfermented sugar, lower alcohol, and increased production of important sensory impact metabolites. 

In fact, a few researchers have reported successfully inducing simultaneous alcoholic and malolactic fermentations (Beelman, 1982 Beelman and Kunkee, 1985 Henick-Kling and Park, 1994). 

When a winery considers investment in laboratory equipment, a compound microscope should be a priority. Microscopic capabilities allow winemakers to quickly monitor the progress of alcoholic and malolactic fermentations and to tentatively determine the source of microbiological problems. This chapter oudines basic microscopy as well as techniques to view wine microorganisms. 

Fig. 6.1. Evolution of lactic acid bacteria population during alcoholic and malolactic fermentation...

The running-off operation consists of recovering the wine which spontaneously flows out of the fermentor by gravity. The wine is then placed in a recipient where alcoholic and malolactic fermentations are completed. 

Table 12.14. Alcoholic and malolactic fermentations in tank results obtained in 1896 (Gayon, 1905)...

The fermentor is emptied and the pomace is pressed. The jnice is then rnn off, the pomace pressed, and the free-rnn and press wines are usually assembled prior to normal alcoholic and malolactic fermentation. 

Dne to their complementary composition, free run wines and press wines should be blended inunediately after pressing, before the completion of alcoholic and malolactic fermentation. Bacterial contamination in the free-run wine, leading to premature malolactic fermentation and the risk of an increase in volatile acidity, is the only reason for fermenting the free-run and press wine separately. Microbiological analysis should be systematic at this stage, followed by sulfiting and reseeding the... 

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