Editing Malolactic fermentation (section)

==Other products produced==
The main products of malolactic fermentation are lactic acid, diacetyl, acetic acid, [[acetoin]], and various [[ester]]s. The amount and exact nature of these products depends on the species/strain of LAB conducting the malolactic fermentation and the condition influencing that wine (pH, available nutrients, oxygen levels, etc.).<ref name="Jacobson"/>

Some strains of ''O. oeni'' can synthesize [[higher alcohols]] which can contribute to fruity notes in the aroma of the wine. Additionally, some strains of the bacterium have [[beta-glucosidase]] enzymes that can break down [[Glucoside|monoglucosides]] which are aroma compounds attached to a sugar molecule. When the sugar component is cleaved, the rest of the compound becomes [[volatilized]], meaning it can potentially [[Olfaction|be detected]] in the aroma bouquet of the wine.<ref name="Wine Micro"/>

In the early 21st century, some strains of ''O. oeni'' were shown to use [[acetaldehyde]] by breaking it down into ethanol or acetic acid. While this may help for wines with excessive levels of acetaldehyde, for red wines, it can also destabilize the color of the wine by interfering with acetaldehyde's reaction with [[anthocyanins]] to create [[polymeric pigments]] that help create a wine's color.<ref name="Wine Micro"/>

===Diacetyl===
[[File:Unstirred and stirred barrels of chardonnay on lees.jpg|left|thumb|Winemakers can encourage diacetyl production by keeping the wine ''sur lie'' in the barrel. The barrel on the right has recently been stirred with a ''bâtonage'' tool.]]

Diacetyl (or 2,3-butanedione) is the compound associated with the "buttery" aromas of Chardonnays, but it can affect any wine that has gone through malolactic fermentation. At an [[odor detection threshold]] of 0.2&nbsp;mg/L in white wines and 2.8&nbsp;mg/L in red wines, it can be perceived as slightly buttery or "nutty" while at concentrations greater than 5 to 7&nbsp;mg/L (5-7 [[Parts-per notation|ppm]]) can overwhelm other [[aroma notes (wine)|aroma notes]] in the wine.<ref name="Wine Faults"/><ref>Martineau, B., Acree, T.E. and Henick-Kling, T ''"[http://www.sciencedirect.com/science/article/pii/096399699590797E Effect of wine type on the detection threshold for diacetyl]"'' Food Research International. Volume 28, Issue 2, 1995, Pages 139–143</ref>

Diacetyl can be produced by the LAB through metabolism of sugar or of [[citric acid]].<ref>Shimazu, Y., Uehara, M., and Watanbe, M. ''"[http://ci.nii.ac.jp/naid/130000026197/ Transformation of Citric Acid to Acetic Acid, Acetoin and Diacetyl by Wine Making Lactic Acid Bacteria]"'' Agricultural and Biological Chemistry 49(7), 2147-2157, 1985</ref> While citric acid is naturally present in grapes, it is in a very small amount with most of it coming from deliberate addition by the winemaker to acidify the wine.<ref name="Boulton"/> In the presence of both malic and citric acids, the LAB use both, but use the malic much more quickly, with the rate of citric use/diacetyl formation influenced by the particular bacterial strain (with most strains of ''O. oeni'' producing less diacetyl than ''Lactobacillus'' and ''Pediococcis'' species), as well as the [[redox]] potential of the wine.<ref>Jan Clair Nielsen and Marianne Richelieu ''"[http://aem.asm.org/content/65/2/740.short Control of Flavor Development in Wine during and after Malolactic Fermentation by Oenococcus oeni]"'' Applied and Environmental Microbiology. February 1999 vol. 65 no. 2 740-745</ref> In wine conditions that have a low redox potential (meaning it is more oxidative such as in a barrel that is not fully topped up), more citric acid will be consumed and diacetyl formed. In more reductive conditions, such as in alcoholic fermentations where yeast populations are at their peak and the wine is heavily saturated with carbon dioxide, the formation of diacetyl is much slower. The yeasts also help keep levels low by consuming diacetyl and reducing it to acetoin and [[butylene glycol]].<ref name="Zoecklein"/>

Diacetyl production is favored in fermentations that run warm with temperatures between {{convert|18|and|25|°C|°F|abbr=on}}. It also tends to be produced at higher levels in wines with lower pH levels (under 3.5), though at levels below 3.2, most strains of LAB desirable for MLF tend to be inhibited. "Wild" (as in uninoculated) malolactic ferments have the potential to produce more diacetyl than inoculated ferments due to the lower initial populations during the [[lag phase]] with inoculated ferments usually having an initial inoculum of 10<sup>6</sup> CFU/mL.<ref name="Wine Micro"/> Late MLF inoculations, after alcoholic fermentation, also tend to produce higher levels of diacetyl.<ref name="Jacobson"/> Chardonnay producers desiring to make the high-diacetyl "buttery style" will often do late or "wild" inoculation in the barrel after primary fermentation, allowing the wine to spend several weeks or even months ''[[sur lie]]'' in reductive conditions that promote diacetyl production.<ref name="Boulton"/> Some sources point out that diacetyl is actually decreased by sur lie, due to surviving yeast metabolizing diacetyl, and therefore malolactic fermentation is best performed apart from lees.<ref>Rotter, Ben. ''"[http://www.brsquared.org/wine/Articles/surlie/surlie.htm Sur lie and bâtonnage (lees contact and stirring)]"''. Improved winemaking, 2008. Retrieved 12-Feb-2016.</ref>

With wines that have excessive levels of diacetyl, some winemakers use sulfur dioxide to bind with the compound and reduce the perception of diacetyl by 30 to 60%. This binding is a reversible process and after only a few weeks [[aging (wine)|aging]] in the bottle or tank, the high levels of diacetyl return. However, sulfur dioxide added earlier in the malolactic fermentation process limits diacetyl production by inhibiting the bacteria and limiting their activity in its entirety, including the conversion of malic to lactic acid.<ref name="Wine Faults"/>