Editing Malolactic fermentation (section)

===Nutritional requirements===
[[File:Sediment at bottom of wine barrel.jpg|right|thumb|When yeast cells die, they sink to the bottom of the tank or barrel, creating the "lees" sediment visible in this picture. The autolysis of the dead yeast cells is a source of a nutrients for lactic acid bacteria.]]
Lactic acid bacteria are [[fastidious organism]]s that cannot synthesize on their own all of their complex nutritional requirements. For LAB to grow and complete malolactic fermentation, the constitution of the wine medium must provide for their nutritional needs. Like wine yeast, LAB require a carbon source for energy metabolism (usually sugar and malic acid), nitrogen source (such as amino acids and [[purine]]s) for [[protein synthesis]], and various vitamins (such as [[Niacin (substance)|niacin]], [[riboflavin]], and [[thiamine]]) and minerals to assist in the synthesis of enzymes and other cellular components.<ref name="Zoecklein"/>

The source for these nutrients is often found in the grape must itself, though MLF inoculations that run concurrent with alcoholic fermentation risk the yeast outcompeting the bacteria for these nutrients. Towards the end of fermentation, while most of the original grape must resources have been consumed, the [[lysis]] of dead yeast cells (the "lees") can be a source for some nutrients, particularly amino acids. Plus, even "dry" wines that have been fermented to dryness still have [[residual sugars|unfermentable pentose sugars]] (such as arabinose, ribose and [[xylose]]) left behind that can be used by both positive and spoilage bacteria. As with wine yeast, manufacturers of cultured LAB inoculum usually offer specially prepared nutritional additives that be used as a supplement. However, [[YAN (wine)|unlike wine yeast]], lactic acid bacteria can not use the supplement [[diammonium phosphate]] as a nitrogen source.<ref name="Wine Micro"/>

Before the introduction of complex nutritional supplements and advances in freeze-dried cultures of LAB, winemakers would cultivate their inoculum of lactic acid bacteria from [[Microbiological culture|culture slants]] provided by laboratories. In the 1960s, these winemakers found it easier to create [[starter cultures]] in media that contained [[apple juice|apple]] or [[tomato juice]]. This "tomato juice factor" was discovered to be a derivative of [[pantothenic acid]], an important [[growth factor]] for the bacteria.<ref name="Boulton"/>

As with yeast, oxygen can be considered a nutrient for LAB, but only in very small amount and only for microaerophilic species such as ''O. oeni''. However, no evidence exists currently to suggest that malolactic fermentation runs more smoothly in aerobic conditions than in complete anaerobic conditions, and in fact, excessive amounts of oxygen can retard growth of LAB by favoring conditions of competing microbes (such as ''Acetobacter'').<ref name="Boulton"/>