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There are three categories of LAB based on the type of fermentation they are capable of (''homolactic'', ''heterolactic'', or both): '''obligatory homofermentative''', '''obligatory heterofermentative''', and '''facultatively heterofermentative'''. ''Obligatory homofermentative'' bacteria only perform ''homolactic'' fermentation, and thus only produce lactic acid. ''Obligatory heterofermentative'' bacteria only perform ''heterolactic'' fermentation, and thus produce lactic acid, CO2, and ethanol (or sometimes acetic acid instead of ethanol). ''Facultatively heterofermentative'' bacteria generally are ''homolactic'' when there is an abundance of carbohydrates, but can also perform ''heterolactic'' fermentation when carbohydrates are not abundant <ref>[https://books.google.com/books?id=6SLB1j0rX78C&pg=PA76&lpg=PA76&dq=what+is+obligatory+facultatively+heterofermentative&source=bl&ots=6E4DB8Px_X&sig=PXZTNO4fB3ifCF_qAl5_I4euKmk&hl=en&sa=X&ei=Z-10VZqvFIWyggTInIHYBw&ved=0CCsQ6AEwAw#v=onepage&q=what%20is%20obligatory%20facultatively%20heterofermentative&f=false Fermentation: Effects on Food Properties. Bhavbhuti M. Mehta, Afaf Kamal-Eldin, Robert Z. Iwanski. CRC Press, Apr 12, 2012. Pg 76.]</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 is 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 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>.