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updated cell density as per Richard Preiss
''P. damnosus'' is sensitive to temperature and pH. It is unable to grow at a pH of 8 or higher or at 35°C. The optimal growth occurs at 22°C and 5.5 pH. ''P. damnosus'' is sensitive to environments that contain NaCl, and will not grow with concentrations of 4% NaCl <ref name="ucdavis"></ref>. Most strains of ''P. claussenii'' can grow in beer. About half of the strains tested of ''P. damnosus'' can grow in beer, and none to very few strains of ''P. acidilactici'', ''P. parvulus'', and ''P. pentosaceus'' have been found to grow in finished beer.
One study showed that optimal growth was observed in [http://www.neogen.com/Acumedia/pdf/ProdInfo/7406_PI.pdf MRS media] with an initial pH of 6.7, and a final pH of 4.14, which occurred naturally from fermentation. The addition of bacteriological peptone, MnSO4, and Tween 80 also increased activity. Maximum cell densities of ''P. damnosus'' are around 1-2 4.3 billion cells/mL in MRS media of a pH of 6.7 ''(editor's note<ref>[https: this maximum //www.facebook.com/groups/MilkTheFunk/permalink/1347683325259878/?comment_id=1349386438422900&reply_comment_id=1350340544994156&comment_tracking=%7B%22tn%22%3A%22R%22%7D Conversation with Richard Preiss on MTF regarding Pediococcus cell density number needs to be verified)'' . 07/19/2016.]</ref><ref>[http://www.ncbi.nlm.nih.gov/pubmed/11851822 Growth optimization of Pediococcus damnosus NCFB 1832 and the influence of pH and nutrients on the production of pediocin PD-1. Nel HA, Bauer R, Vandamme EJ, Dicks LM. 2001.]</ref>, but this is only in optimal conditions. Maximum cell density varies based on the conditions of the propagation with pH and nutrient demands being two of the main limiting factors <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>.
Although more experiments are probably needed, agitation is believed to be an important factor for any species of microbe (yeast and bacteria). Gentle stirring on a stir plate or orbital shaker, or frequent gentle manual agitation leads to faster growth and a higher number of organisms. Agitation keeps the microbes in solution. It also maximizes the microbes' access to nutrients and disperses waste evenly. In a non-agitated starter, the microbes are limited to the diffusion rate of nutrients, leading to a slower and more stressful growth <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1168024059892473/?comment_id=1174865305875015&reply_comment_id=1176092372418975&total_comments=1&comment_tracking=%7B%22tn%22%3A%22R9%22%7D Conversation with Bryan of Sui Generis Blog about starters and agitation. 11/09/2015.]</ref>. Although ''Pediococcus'' are generally considered facultative anaerobes and oxygen usually does not negatively affect their growth, some strains may show less growth in the presence of oxygen and are considered anaerophilic, meaning that the presence of oxygen inhibits their growth (and therefore their acid production) but they can still grow in the presence of O2. The presence of CO2 has a positive effect on acid production <ref name="NAKAGAWA"></ref> . Therefore, it is generally best practice to seal the starter with an airlock.