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[[file:Salmonella_micrograph.jpg|thumb|left|Electron micrograph of the enteric bacteria Salmonella (pink rods).]]
Lambic wort arrives in the [[koelschip]] at approximately 5% sugar per weight of water, along with an assortment of proteins and fatty acids and other compounds.<ref name=Erbe />T. Erbe and H. Brückner, [http://www.sciencedirect.com/science/article/pii/S0021967300002557| Chromatographic determination of amino acid enantiomers in beers and raw materials used for their manufacture], 2000</ref> Negligible ethanol is present prior to fermentation, nor is there much of the organic acids that will give lambic its characteristic tartness; the wort has a pH around 5, which is similar to the wort of other beers.<ref name=Oevelen77 /> Enteric bacteria, including Enterobacter hormaechei, E. kobei, Klebsiella pneumoniae, and Escherichia coli, are the first to gain a foothold in this environment, with significant numbers found after three to four days. The enteric bacteria primarily consume glucose, which reduces the gravity of the wort from ~1.050 to ~1.040 after the first three weeks.
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 />
Conversely, it has been found that spontaneous fermentations in similar worts in other parts of the world follow similar overall trends.<ref name=AWAs /> Yeasts such as Saccharomyces and Brettanomyces and bacteria such as the enterobacteria and Pediococcus are cosmopolitan throughout the world, and all are similar enough to be classified into the same genus by both phenotype and genotype. However, the large degree of geographic separation coupled with the rapid evolutionary rates of these organisms will still lead to measurable changes in both. This is highlighted in the fact that while many lambic-like beers have been brewed in other parts of the world, and are often very similar to lambic itself, they still possess noticeably different sensory characteristics. This can be likened to terroir in wine, as the local microbiome in one location will produce a similar, but not identical, product to that in another location.
As an example, Brettanomyces shows significant genomic variation between strains, as well as a corresponding variability in their metabolisms, indicating that different strains of Brettanomyces bruxellensis will lend markedly different sensory characteristics to lambic.<ref name = Conterno1> L. Conterno, C. M. L. Joseph, T. J. Arvik, T. Henick-Kling, and L. F. Bisson [http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0CC0QFjAB&url=http%3A%2F%2Fwww.researchgate.net%2Fprofile%2FC_M_Joseph%2Fpublication%2F236843438_Genetic_and_Physiological_Characterization_of_Brettanomyces_bruxellensis_Strains_Isolated_from_Wines%2Flinks%2F0c960528eb2e4a0513000000.pdf&ei=t6HKVJbHJZWyoQT2qoCYBg&usg=AFQjCNFMfoISmHrGfWtGfDHJWJI4w25vOw&sig2=u9Loxwy3zVWXK4gy8vn_2g&bvm=bv.84607526,d.cGU| Genetic and Physiological Characterization of Brettanomyces bruxellensis Strains Isolated from Wines], 2006</ref><ref name=Borneman1> A. R. Borneman, R. Zeppel, P. J. Chambers, C. D. Curtin [http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1004161| Insights into the Dekkera bruxellensis Genomic Landscape: Comparative Genomics Reveals Variations in Ploidy and Nutrient Utilisation Potential amongst Wine Isolates], 2014</ref><ref name = Yakobson> [http://www.brettanomycesproject.com/dissertation/ Brettanomyces Project Dissertation], Chad Michael Yakobson</ref><ref name = Curtin> C. D. Curtin, J. R. Bellon, P. A. Henschke, P. W. Godden, and M. A. de Barros Lopes [http://www.pubfacts.com/detail/17233769/Genetic-diversity-of-Dekkera-bruxellensis-yeasts-isolated-from-Australian-wineries.| Genetic diversity of Dekkera bruxellensis yeasts isolated from Australian wineries], 2007</ref><ref name = Agnolucci> M. Agnolucci, I. Vigentini, G. Capurso, A. Merico, A. Tirelli, C. Compagno, R. Foschino, M. Nuti [http://www.researchgate.net/publication/222660112_Genetic_diversity_and_physiological_traits_of_Brettanomyces_bruxellensis_strains_isolated_from_Tuscan_Sangiovese_wines| Genetic diversity and physiological traits of Brettanomyces bruxellensis strains isolated from Tuscan Sangiovese wines], 2009</ref>
==Seasonal variation==