Malolactic fermentation temperature

Delaquis, R, Cliff, M., King, M., Girare, B., Hall, J., Reynolds, A. (2000). Effect of two commercial malolactic cultures on the chemical and sensory properties of Chancellor wines vinified with different yeasts and fermentation temperatures. Am. J. EnoL Vitic., 51, 42 8. 

Figure 1.19 Mass spectra of acetaldehyde PFB-oxime (a), diacetyl mono PFB-oxime (b), acetoin PFB-oxime derivative (c), and o-chlorobenzaldehyde PFB-oxime (d) recorded in the GC/MS analysis of standard solution performed in positive ion chemical ionization mode using methane as reagent gas (reagent gas flow 1 mL/min ion source temperature 200 °C). Flamini et al., (2005) Monitoring of the principal carbonyl compounds involved in malolactic fermentation of wine by synthesis of 0-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine derivatives and solid-phase-microextraction positive-ion-chemical-ionization mass spectrometry analysis, Journal of Mass Spectrometry, 40, p. 1561. Copyright John Wiley Sons, Ltd. Reproduced with permission...

Control of storage temperature post-fermentation is also important, particularly for white wines for which malolactic fermentation is undesirable. The storage temperature of wine influences oxidation (which is irreversible), the rate of which is reduced by approximately 20% for each 10°C reduction in temperature. The hydrolysis of carboxylic acid esters is similarly decreased by approximately 50% (White, 1989). It is now recommended that from crushing to bottling, the juice and wine should be stored at a controlled temperature in the range 10-18°C. 

Clarification can be used to reduce populations of non-Saccharomyces yeasts (Mora and Mulet, 1991). Although populations are initially reduced, growth of these yeasts may continue during cold-clarification and actually lead to denser populations than expected. Many of these yeasts may also be active during the course of fermentations conducted at lower temperatures (Section 6.2.2). The presence of insoluble solids in musts also influences subsequent malolactic fermentations (Liu and Gallander, 1982). Here, the authors reported that MLF was most rapid in wines fermented with the highest amount of solids. 

In spite of all precautions, a stuck fermentation may still occur. In this case, white wines must be treated differently from reds which undergo malolactic fermentation. At the time of the stuck fermentation, the red wine tank contains must and pomace rich in bacteria. The wine should be drained rapidly, even if the skin and seed maceration is not complete. Draining eliminates part of the bacterial contamination and introduces oxygen, which favors the restarting of fermentation and decreases the temperature. The wine can be sulfited at the same time, to inhibit bacterial development. In some cases, the fermentation restarts spontaneously. 

The ideal temperature for lactic acid bacteria growth (notably O. oeni) and for malic add degradation in wine is around 20°C. An excessive temperature of 25°C or above always slows malolactic fermentation—principally by inhibiting the bacterial biomass. Additionally, an excessive temperature increases the risk of bacterial spoilage and increased volatile acidity. In practice, therefore, maintaining a wine at 20°C is recommended. It should not be allowed to cool too much after alcoholic fermentation. If the temperature of the winery decreases, the wine should be warmed. 

When the temperature is less than 18°C, the initiation of malolactic fermentation is delayed and its duration is longer. A malolactic fermentation under way can continue even in a wine with a temperature between 10 and 15°C. In these cases, the bacterial biomass was normally constituted under favorable conditions. The cooling blocks the multiplication of bacteria but does not eliminate... 

Along with pH, temperature is certainly the factor that most strongly influences the malolactic fermentation speed of a properly vinified wine not excessively sulfited. This factor is also the most easily monitored and controlled. 

The malolactic fermentation phase begins during the growth phase, as soon as the total population exceeds lO UFC/ml. It continues and is completed during the stationary phase, or sometimes at the beginning of the death phase. In very favorable conditions with a limited concentration of malic acid, malolactic fermentations are often completed even before the end of the growth phase. The optimum population in these cases exceeds 10 UFC/ml. As soon as a sufficient biomass is formed, malic acid is degraded. The malolactic acid bacterial activity is always present but depends on various conditions, especially the temperature. The transformation of 2 g of malic acid per liter can take more time than 4 g/1 if the population level attained is lower. 

Since the late 1990s, it has become increasingly popular to run the wine off into barrel immediately (Section 12.7.2), as malolactic fermentation in wood has been shown to enhance aromatic complexity as well as the finesse of oak character. In fact, it is not known whether this undisputed improvement is due to the effect of bacteria on molecules released by the oak, or the fact that the new wine is stiU warm when it is put into barrel. The fact remains that, if red wines are to be barrel-aged, they should be run off into barrel as soon as possible. We now have all the necessary techniques to avoid the problems that led to the abandomnent of barrel-aging in the past blending, temperature control, analytical monitoring of fermentation in individual barrels, etc. 

Conditions Required for Malolactic Fermentation Influence of Acidity, Temperature, Aeration and Sulfiting... 

The following factors participate in the control of malolactic fermentation acidity (Section 6.2.1), temperature (Section 6.2.4), aeration (Section 6.2.5), vatting time and sulfiting (Section 6.2.2). 

New wines should therefore be maintained at a temperature of at least 18°C. Temperature is the simplest means of influencing malolactic fermentation. In the past, the wine cellars were not temperature-controlled and the cold autumn air was the principal factor blocking malolactic fermentations. 

The fermentation of malic acid is slow at 15°C, whereas it is complete in a few days at 20°C. When initiated at a suitable temperature, malolactic fermentation is generally completed, even when the temperature drops to 10°C. Its initiation in winter is unlikely if the temperatures are unfavorable fermentation will most likely occur the following spring, when the temperature rises natorally. Sulfiting should be carefully timed to avoid blocking this phenomenon. 

The fermentation should be conducted at as low of a temperature as possible (18-20°C, for example). The low temperature makes malolactic fermentation slower but limits the risk of bacterial spoilage—in particular, excessive volatile acidity production due to the trausformation of substauces other than mafic acid. 

The temperature must be maintained while waiting for spontaneous malolactic fermentation and this can become costly. Finally, indigenous bacteria are not necessarily higher in quality than commercial strains an inoculation with selected strains could be preferable. 

There are several advantages to this method. The quality of the products is at least identical, if not superior, to that from traditional winemaking space, labor and material are saved temperature increases are less significant malolactic fermentation is facilitated and the control of the operations is grouped together and therefore more efficient. 

If malolactic fermentation is not desired, the wine temperature is lowered to around 12°C. The lees are stirred daily by agitation or pnmping, avoiding oxygen dissolution. This operation makes use of the reducing power of yeast lees to protect wine from oxidation. The formation of reduction odors in the lees is simultaneonsly avoided (Section 13.9). 

However, it is not always easy to start malolactic fermentation at the right time in wines with very high acidity (Section 13.7.6) and it is essential to adjust the SO2 content and temperature for that purpose. It is also possible to inoculate a properly prepared starter, but this is a rather laborious operation. Seeding with reactivated bacterial biomass, initially developed for red wines (Section 12.7.5), has considerably improved malolactic fermentation conditions in Champagne base wines (Laurent and Valade, 1993) and snitable products are now commercially available. 

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