Changes

Maximum cell densities of ''Pediococcus'' and ''Lactobacillus'' are around 1-9 billion cells/mL, depending on the available nutrients (amino acids and FAN) in the growth media <ref name="Peyer">[http://www.asbcnet.org/publications/journal/vol/2015/Pages/ASBCJ-2015-0811-01.aspx Growth Study, Metabolite Development, and Organoleptic Profile of a Malt-Based Substrate Fermented by Lactic Acid Bacteria. ​Lorenzo C. Peyer, Emanuele Zannini, Fritz Jacob, and Elke K. Arendt. 2015.]</ref><ref>[https://www.reddit.com/r/Homebrewing/comments/3qp7b7/advanced_brewers_round_table_neva_parker_white/cwh7iqq Neva Parker, Reddit thread. 10/29/2015.]</ref>. Cell growth rates concur with a drop in pH and a rise in [[Titratable_Acidity|titratable acidity]]. Brewer's wort has shown to be a nutritionally adequate growth medium for ''Lactobacillus''. Both growth and the the lowering of pH begin to stabilize around 12-48 hours (assuming the ''Lactobacillus'' does not have any yeast to compete with). Titratable acidity will also rise drastically during growth, but will also continue to rise after growth has completed. The maximum growth that a particular species or strain is capable of might be explained by its pH tolerance, and thus its ability to produce more acid. For example, ''L. plantarum'' has been shown to grow in a very low pH environment (3.37-3.0 pH, depending on strain) due to their ability to better control large pH gradients between the cytoplasma and the external environment. This has been shown in the [[Lactobacillus#Commercially_available_Lactobacillus_strains_and_their_pH_change_over_time|above data provided by Matt Humbard]], as well as this reference <ref name="Peyer"></ref>. Thomas Hübbe's masters thesis showed that a strain of ''L. brevis'' had a spike of growth after 50 hours, and then a small dip in cell count after 96 hours, at which time the cell count remained consistent for at least 528 hours <ref name="Hubbe"></ref>.  Cell growth can also be influenced by the presence of other microorganisms, such as ''Saccharomyces'' and ''Brettanomyces''. One study by Hübbe showed that ''L. brevis'' and ''L. parabrevis'' grew to the normal high cell counts when grown individually and without competition. When co-fermented with ''Brettanomyces'', the cell count of ''L. brevis'' was halved, and the growth rate of ''L. parabrevis'' was greatly diminished to about 15-20% (the pitching rate of ''Brettanomyces'' was also tested, and seemed to not have an effect on the ''Lactobacillus'' growth). When co-fermented with both ''S. cerevisiae'' and ''Brettanomyces'', the ''Lactobacillus'' growth was greatly diminished to about 2-13% of what the normal cell growth was without competition. This appears to correspond with anecdotal reports from brewers that some ''Lactobacillus'' species/strains do not compete well with yeast, especially ''S. cerevisiae'' <ref name="Hubbe"></ref>.