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Enteric bacteria are responsible for the production of [[acetic acid]], and the pH of the wort falls from around 5 to 4.5 in the first week of fermentation. The 40 to 120 mg/L acetic acid found in the wort after the first week is very close to the amount found in the final product.<ref name=Oevelen77 />
<ref name=sour> J. Edwards and A. DiCaprio. [http://www.process-nmr.com/Presentation/Edwards%20-%20SMASH%202014%20-%20MNova%20Users%20Meeting%20-%209-7-14.pdf | When Beer Goes Sour: An NMR Investigation], Mestrelab
MNova Users Meeting, SMASH – Atlanta, GA, September 7, 2014</ref> Significant changes to the concentration of acetic acid should not occur until the ethanol has a chance to oxidize in aging in the bottle over many years or even decades.<ref name=Vanderhaegen1> B. Vanderhaegen, H. Neven, H. Verachtert, G. Derdelinckx [http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCAQFjAA&url=http%3A%2F%2Fwww.researchgate.net%2Fprofile%2FGuy_Derdelinckx%2Fpublication%2F222839054_The_chemistry_of_beer_aging__a_critical_review%2Flinks%2F0c960523339c4b25a6000000.pdf&ei=Tq3IVKmfFcGyogSs_YLQCA&usg=AFQjCNFaBrvqDGjqEV2I9uQ73dYh_ParXg&sig2=Z8dY4iDHozbT1eb9JeAdrw&bvm=bv.84607526,d.cGU | The chemistry of beer aging – a critical review], 2006</ref><ref name = Werner> Werner Van Obberghen, '''2. Het algemene productieproces van bier'''</ref> The pellicle that forms on the top of the wort may be the product of acetobacteria during the enteric phase,[9] though most other sources inidcate indicate that the pellicle is the result of Brettanomyces (with Pichia and Candida).<ref name="Guinard">Jean-Xavier Guinard, [[Books#Classic Beer Styles: Lambic|Classic Beer Styles: Lambic]], 1990</ref>
Low pH (below ~4.5) and an ethanol concentration higher than ~2% by volume is a hostile environment to the enterobacteria, and Saccharomyces species are able to dominate the flora in the wort once these conditions occur around 30 to 60 days into fermentation.
The microbes found in lambic may come from a variety of sources, as nearly every surface and even the air found in the brewery are teeming with life. While the air above the [[koelschip]] is often cited as the source of the microorganisms in lambic, other sources are now known to play a significant role.
While there are many potential places that the wort can aquire acquire its characteristic flora, some primary reservoirs to consider are:
# The air over the wort and in the cellar where the wort is aged.
Little research exists correlating the season of brewing to changes in the microbiology and chemistry of lambic; however, a delay in the appearance of the late-fermentation bacterial flora in lambic was observed when fermentation started earlier in the brewing season, leading to cooler fermentation temperatures.<ref name=Spitaels /> The flora were indistinguishible after 18 months.
Similarly, a study on spontaneously fermented ales in the United States revealed marked differences between ales brewed in the spring versus those in the winter.<ref name=AWAs /> The flora broadly follow the same pattern of succession regardless of the season of innoculationinoculation, although genetic analysis showed distinct differences between the flora responsible for fermentation occurring in the spring versus the winter. The differences between the organisms found in the wort innoculated inoculated at different seasons were largest in the early stages of fermentation and by 36 weeks, there was no longer a significant difference in the flora of in either season's wort.
=Other spontaneous fermentations=