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updated "Contamination Concerns"
Another very typical contaminate during souring wort with ''Lactobacillus'' is actually brewer's yeast (''S. cerevisiae''). Brewer's yeast is not greatly inhibited by ''Lactobacillus''. Conversely,''Lactobacillus'' is greatly inhibited by the presence of active ''S. cerevisiae'' <ref name="Hubbe">[https://www.facebook.com/groups/MilkTheFunk/1407620505932826/ Effect of mixed cultures on microbiological development in Berliner Weisse (master thesis). Thomas Hübbe. 2016.]</ref>, and the warmer temperatures encourage ''S. cerevisiae'' to ferment the wort quickly. This often results in a beer that isn't sour because the ''Lactobacillus'' are out-competed by the yeast. Signs that yeast has contaminated the wort include the typical signs of yeast fermentation: the presence of a krausen, a gravity shift of more than 1.005 gravity points (or 0.5-1.0° Plato), and looking at a sample of the wort under a microscope. Sources of yeast contamination can come from poor sanitation, but they can also come from the yeast manufacturer themselves. See see [[100%25_Lactobacillus_Fermentation|100% ''Lactobacillus'' fermentation]] for more information.
Another source of contamination, which can arguably be considered not actually a contamination, is when using some sort of "wild" source for the ''Lactobacillus''. For example, when culturing ''Lactobacillus'' from grains, fruit, or from some other fermented food such as kefir, sauerkraut, etc. using non-plating techniques (see [[Alternative Bacteria Sources]]), yeast and other microbes can carry over from the culturing process. The only way to guarantee that only ''Lactobacillus'' from a "wild" source such as these will be fermenting the wort, it must be isolated first using plating techniques (see [[Wild Yeast Isolation]]. Otherwise there is a chance that wild yeast will also survive the culturing process.
===Preventing Contamination===