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All metabolism by Lactobacillus, including growth, will require sugar to be consumed and lactate (lactic acid) to be produced. Two categories of metabolism exist, '''homofermentative''' and '''heterofermentative'''. ''Homofermentative'' metabolism is described as the cell catabolizing one molecule of glucose to yield two molecules of pyruvate, which is reduced to two molecules of lactate (lactic acid). ''Heterofermentative'' metabolism is described as the cell catabolizing one molecule of glucose into one molecule of CO2, one molecule of glyceraldehyde phosphate, and one molecule of acetyl phosphate. The molecule of glyceraldehyde phosphate is reduced to one molecule of lactate, and the acetyl phosphate is reduced to on molecule of ethanol. In summary, ''homofermentative'' LAB produces only lactic acid, while ''heterofermentative'' LAB produce lactic acid, CO2, and ethanol <ref>[http://textbookofbacteriology.net/lactics_2.html Todar's Online Texbook of Bacteriology. Kenneth Todar, PhD. Retrieved 05/06/2015.]</ref>.
It is worth noting that the amount of CO2 produced is very small in ''heterofermentative'' species. Lance Shaner of Omega Yeast Labs noted that although L. brevis and L. plantarum are classified as ''heterofermentative'', the human eye cannot detect any CO2 production in the Omega Yeast Lactobacillus blend (OYL-605). Lance still needs to test this blend to see if it does produce any produce CO2. It is clear though that a ''heterofermentative'' bacteria cannot produce a krausen, which is often seen with the use of other Lactobacillus cultures. If a krausen develops in wort when only a Lactobacillus culture is pitched and no Saccharomyces is pitched, this is indicative of cross contamination of Saccharomyces in the Lactobacillus culture <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1083842231643990/?comment_id=1084646124896934&offset=0&total_comments=26&comment_tracking=%7B%22tn%22%3A%22R8%22%7D Discussion with Lance Shaner on MTF. 6/7/2015.]</ref>.
==See Also==