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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, '''homolactic''' and '''heterolactic'''. In summary, ''homolactic'' fermentation produces only lactic acid, while ''heterolactic'' fermentation produce lactic acid, CO2, and ethanol/acetic acid <ref name="Todar">[http://textbookofbacteriology.net/lactics_2.html Todar's Online Texbook of Bacteriology. Kenneth Todar, PhD. Retrieved 05/06/2015.]</ref>.

''Homolactic'' metabolism is described as the cell catabolizing one molecule of glucose to yield two molecules of pyruvate, which is then further reduced to two molecules of lactate (lactic acid). ''Homolactic'' fermentation only allows the fermentation of hexoses (glucose, mannose, etc.). ''Homolactic'' metabolism follows the ''Embden-Meyerhof-Parnas'' pathway <ref name="Effects on Food Properties"></ref>.

''Heterolactic'' 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 one molecule of ethanol (or one molecule of acetic acid instead of ethanol, depending on its growing environment <ref name="Raunak">[https://raunakms.wordpress.com/2011/01/30/lactic-acid-bacteria/ Lactic Acid Bacteria. Raunak Shrestha. Retrieved 6/7/2015.]</ref>). ''Heterolactic'' fermentation allows the fermentation of hexoses and pentoses <ref>[https://books.google.com/books?id=eZjIfud742wC&pg=PA33&lpg=PA33&dq=facultative+heterofermentative&source=bl&ots=QQYpzpsrvC&sig=kkyP7wUjgWiE2UV2qkIaRyxMMGA&hl=en&sa=X&ei=K_d0VYDJPLX9sATv_IXgAQ&ved=0CDIQ6AEwBDgK#v=onepage&q=facultative%20heterofermentative&f=false Handbook of Dough Fermentations. Karel Kulp, Klaus Lorenz. CRC Press, May 20, 2003. Pg 33.]</ref>. ''Heterolactic'' fermentation follows the ''pentose phosphate'' pathway, or also called the ''"phosphogluconate'' pathway " <ref name="Effects on Food Properties"></ref>.

There are three categories of ''Lactobacillus'' based on the type of fermentation they are capable of (''homolactic'', ''heterolactic'', or both).

# '''Obligatory homofermentative''' Lactobacillus only perform ''homolactic'' fermentation, and thus only produce lactic acid <ref name="Effects on Food Properties"></ref>. # '''Obligatory heterofermentative''' Lactobacillus only perform ''heterolactic'' fermentation, and thus produce lactic acid, CO2, and ethanol (or sometimes acetic acid instead of ethanol) <ref name="Effects on Food Properties"></ref>. # '''Facultatively heterofermentative''' Lactobacillus generally are ''homolactic'homolacti' when there is an abundance of carbohydrates, but can also perform ''heterolactic'' fermentation when carbohydrates are not abundant <ref name="Effects on Food Properties"></ref>.

Other factors can determine if a ''facultative heterofermentative'' species uses ''homolactic'' or ''heterolactic'' fermentation. For example, L. plantarum, which is a ''facultatively heterofermentative'' species, is ''homolactic'' without the presence of oxygen. In the presence of oxygen, however, it performs ''heterolactic'' fermentation, and produces acetic acid <ref>[https://microbewiki.kenyon.edu/index.php/Lactobacillus_plantarum_and_its_biological_implications Lactobacillus plantarum and its biological implications. Microbe Wiki. Retrieved 6/7/2015.]</ref><ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1083842231643990/?comment_id=1084922688202611&offset=0&total_comments=28&comment_tracking=%7B%22tn%22%3A%22R%22%7D Conversation with Lance Shaner about L. plantarum on MTF. 6/7/2015.]</ref>.

* All types of ''Lactobacillus'' produce different levels of ''secondary metabolites'' (compounds that are not required for the organism to live <ref>[http://en.wikipedia.org/wiki/Secondary_metabolite Secondary Metabolite. Wikipedia. Retrieved 6/9/2015.]</ref>) in addition to the primary metabolites discussed above. These include acetaldehyde, diacetyl, fusel alcohols, and many more compounds (see [http://phdinbeer.com/2015/04/13/physiology-of-flavors-in-beer-lactobacillus-species/ Matt's article] for more details).