L- and D-lactate by glycolysis. However, in the absence of glucose, some species, such as P. pentosaceus, begin using glycerol, degrading it into pyruvate which later can be converted to diacetyl, acetate, 2,3-butanediol and other compounds that can impart unfavorable characteristics to the wine. Most Pediococcus species are undesirable in winemaking due to the high levels of diacetyl that can be produced, as well as increased production of biogenic amines that has been implicated as one potential cause for red wine headaches. Many species of Pediococcus also have the potential to introduce off odors or other wine faults to the wine such as the bitter-tasting "acrolein taint" that comes from degradation of glycerol into acrolein which then reacts with phenolic compounds in the wine to produce a bitter-tasting compound. One species, P. parvulus, has been found in wines that have not gone through MLF (meaning malic acid is still present in the wine), but has still had its bouquet altered in a way that enologist have described as "not spoiled" or flaw. Other studies have isolated P. parvulus from wines that have gone through malolactic fermentation without the development of off odors or wine faults. Nutritional requirements Lactic acid bacteria are fastidious organisms 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 purines) for protein synthesis, and various vitamins (such as niacin, riboflavin, and thiamine) and minerals to assist in the synthesis of enzymes and other cellular components. 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 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