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Some species/strains of ''Lactobacillus'' can create their own amino acids (this is to say they are ''prototrophic''), whereas other species/strains cannot (this is to say they are ''autotrophic''). ''Autotrophic Lacto'' can break down proteins, including foam forming proteins, in beer through a process called ''proteolysis'' <ref name="Todar"></ref>, the breakdown of various proteins into smaller polypeptides or amino acids through the use of various enzymes <ref>[https://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/26351/ShellhammerThomasH.FoodScience.TextureProteolysisViable.pdf?sequence=1 Texture, proteolysis and viable lactic acid bacteria in commercial Cheddar cheeses treated with high pressure. Cheryl Wick, Uwe Nienaber, Olga Anggraeni, Thomas H Shellhammer and Polly D Courtney. 2002. Retrieved 7/7/2015.]</ref><ref name="Haq_Mukhtar">[http://www.researchgate.net/profile/Hamid_Mukhtar4/publication/230245468_PROTEASE_BIOSYNTHESIS_FROM_LACTOBACILLUS_SPECIES_FERMENTATION_PARAMETERS_AND_KINETICS/links/00b7d52c403b158288000000.pdf Protease Biosynthesis from Lactobacillus Species: Fermentation Parameters and Kinetics. Ikram-Ul_Haq and Hamid Mukhtar. Jan 2007. Retrieved 7/7/2015.] </ref><ref>[https://en.wikipedia.org/wiki/Proteolysis Proteolysis. Wikipedia. Retrieved 7/7/2015.]</ref>. Both ''homofermentative'' and ''heterofermentative'' species have been observed to have ''proteolytic activity'' <ref>[https://books.google.com/books?id=qMreBwAAQBAJ&pg=PA133&lpg=PA133&dq=lactobacillus+homofermentative+proteolytic&source=bl&ots=bjxq9rGdha&sig=pCz4WeKek3zTv5oL6Rui1dUuEqw&hl=en&sa=X&ei=AJqcVeT0O8XkoAS0-oC4CQ&ved=0CF0Q6AEwBw#v=onepage&q=lactobacillus%20homofermentative%20proteolytic&f=false Brewing Microbiology. Fergus Priest. Springer Science & Business Media, Jun 29, 2013. Pg 133.]</ref>. This process is a large part of cheese and yogurt fermentation. ''Lactobacillus'' species that have been identified as breaking down proteins (mostly in cheese or yogurt) include ''Lactobacillus bulgaricus'', ''Lactobacillus rhamnosus'', ''Lactobacillus casei'', ''Lactobacillus paracasei'', ''Lactobacillus helveticus'', ''Lactobacillus delbrueckii'', ''Lactobacillus brevis'', ''Lactobacillus cellobiosus'', ''Lactobacillus fermentum'', and ''Lactobacillus plantarum'' <ref name="Haq_Mukhtar"></ref>. Results of using various species/strains appears to demonstrate that different species/strains are worse for degrading head retention proteins than others. For example, it's been reported that B.H. Meyer says that souring with ''L. delbruekii'' creates better head retention than souring with other species such as ''L. brevis''. <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1105663546128525/?comment_id=1105772812784265&offset=0&total_comments=107&comment_tracking=%7B%22tn%22%3A%22R9%22%7D Conversation with Kristen England on MTF. 7/7/2015.]</ref><ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1096427697052110/?comment_id=1096496983711848&offset=0&total_comments=45&comment_tracking=%7B%22tn%22%3A%22R9%22%7D Conversation with Jace Marti on MTF about L. delbruekii head retention problems. 6/21/2015.]</ref>. Different strains of the same species may also have different proteolytic activity <ref>[http://www.ncbi.nlm.nih.gov/pubmed/8568030 Comparison of proteolytic activities in various lactobacilli. Sasaki M, Bosman BW, Tan PS. 1995.]</ref>.
''Proteolytic activity'' has been shown to decrease as pH falls below 5.0 for some species of ''Lactobacillus'' <ref name="Haq_Mukhtar"></ref>. In order to combat poor head retention in beers that are soured with ''Lacto'', it has been suggested by German brewing scientist, Burghard Hagen Meyer, to lower the pH of the wort before pitching ''Lactobacillus'' <ref name="Gail">[https://sourbrewster.wordpress.com/2012/09/18/berliner-weisse-the-old-time-kettle-souring-technique/ ''Berliner Weisse – the old-time kettle-souring technique.'' Brewing Sour blog, by Gail Ann Williams.September 18, 2012. Retrieved 7/7/2015.]</ref><ref>[http://ingenuitybrew.blogspot.com/2013/06/berliner-weisse-test.html ''Berliner Weisse Test''. Ingenuity Brew Blog. June 4, 2013. Retrieved 7/7/2015.</ref><ref>[http://www.themadfermentationist.com/2012/06/100-lactobacillus-berliner-weisse.html ''100% Lactobacillus Berliner Weisse.'' The Mad Fermentationist Blog, by Michael Tonsmeire. June 25, 2012. Retrieved 7/7/2015.]</ref>. Additionally, using ingredients that increase head retention such as unmalted chit, malted wheat, and carafoam have been used to help combat poor head retention in beers soured by ''Lactobacillus'' <ref name="Gail"></ref><ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1105839682777578/?comment_id=1105942362767310&offset=0&total_comments=27&comment_tracking=%7B%22tn%22%3A%22R8%22%7D Conversation with Richard Preiss on MTF. 7/7/2015.]</ref>. Professional brewer [https://www.facebook.com/groups/MilkTheFunk/permalink/1105839682777578/ Kristen England] tested [http://www.mbaa.com/districts/MidSouth/mash/Documents/2014%20PDF%20Hop%20Product%20Applications%20Presentation.pdf?Mobile=1&Source=%2Fdistricts%2FMidSouth%2Fmash%2F_layouts%2Fmobile%2Fview.aspx%3FList%3D85ff6384-aa05-491f-8ef3-d2e9eea713f2%26View%3Da234a10f-469b-4edd-a8a9-9a96b00750ee%26CurrentPage%3D1 Hexa Iso Hop Extract] by dosing at 4 times the recommended dosage and found that it greatly increased head retention in a Berliner Weisse (3.5% abv, pH 3.1, TA ~1, BU 5), with a minor taste difference. Kristen recommends experimenting with lower dosages to avoid too much flavor impact.