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Another source of contamination, which is arguably desired, happens when using a "wild" source of ''Lactobacillus''. For example, when culturing ''Lactobacillus'' using non-plating techniques from grains, fruit, or from some other fermented food such as kefir, sauerkraut, etc., yeast and other microbes can carry over from the culturing process (see [[Alternative Bacteria Sources]]). The only way to guarantee that only ''Lactobacillus'' from a "wild" source such as this ferment the wort, is to isolate the microbe using plating techniques (see [[Wild Yeast Isolation]]). Otherwise, there is a chance that wild yeast will also survive the culturing process.
Oxidative species of yeast can also contaminate wort that is being soured. Their fermentation can resemble that of brewer's yeast visually, however, they often do not attenuate wort. See [https://www.facebook.com/groups/MilkTheFunk/permalink/2502846349743564/?comment_id=2502876486407217&reply_comment_id=2508235855871280&comment_tracking=%7B%22tn%22%3A%22R%22%7D Dr. Bryan Heit's brief biochemistry explanation for "krausen" or "pellicles" caused by oxidative yeast and why it does they do not correspond with a drop in gravityif they are formed by oxidative yeast species]. Oxidative yeast may produce off-flavors, but not always.
===Preventing Contamination===