Changes

Lactic acid is the primary metabolite for ''Lactobacillus'', as well as CO2 and ethanol/acetate (acetic acid) in heterofermentative species. Acid production is at it's highest during the exponential growth phase, but continues into the stationary and decline phases. Typically just under 50% of the lactic acid produced is L-lactic acid (more nutritionally relevant) while the slight majority is D-lactic acid <ref name="Peyer"></ref>. The amount of lactic and acetic acids produced varies from species to species. For example, the referenced study showed that ''L. plantarum'' produces more than twice the amount of lactic acid than ''L. brevis'', and ''L. reuteri'' produced slightly more lactic acid than ''L. brevis''. ''L. reuteri'' produced around twice as much acetic acid than ''L. brevis'', and ''L. plantarum'' produced very little acetic acid. The small amount of acetic acid produced by ''L. plantarum'' in this study was explained by oxygen exposure during sampling, while the obligate heterofermentative species (''L. reuteri'' and ''L. brevis'') produced acetic acid as a direct result of their heterolactic fermentation <ref name="Peyer"></ref>. Santeri Tenhovirta's master thesis where he soured wort with several species of ''Lactobacillus''without purging the air out of the headspace, followed by fermenting it unpasteurized with US-05, reported 8 mg/ml of lactic acid in the ''L. rhamnosus'' sample, 7 mg/ml in the ''L. plantarum'' and ''L. alimentarius'' samples, and 5 mg/ml in the ''L. brevis'' and ''L. buchneri'' samples . None of the samples had significant acetic acid production, except for ''L. brevis'' which produced 0.3 mg/ml and the ''L. buchneri'' which produced 1.3 mg/ml <ref name="Tenhovirta_masters" />.