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==Contamination Concerns==
When working with lactic acid-producing bacteria, the brewer’s goal is usually to attain clean-tasting sourness, while obtaining desirable flavor contributions from these bacteria, and simultaneously minimizing off-flavors. It should be noted that off flavors span the range from undesired by most, to desirable to some. For example, isovaleric acid is a compound known for its footy aroma that would be considered an off flavor in many beers, yet it gives a highly desired flavor to certain French cheeses and is aceptable by some in small amounts in mixed fermentation beer.
With that said, contamination issues are among the biggest challenges when pre-souring wort with ''Lactobacillus''. This is because ''Lactobacillus'' does not fully ferment wort by itself (see [[100%25_Lactobacillus_Fermentation|100% ''Lactobacillus'' fermentation]]). When yeast fully ferments wort into beer, alcohol, hops, and a low pH all work together to prevent most spoilage microorganisms from contaminating the beer (although contamination can certainly happen with beer spoilage microbes such as ''Brettanomyces'', ''Pediococcus'', etc.) <ref>[http://suigenerisbrewing.blogspot.com/2014/02/fact-or-fiction-can-pathogens-survive.html "Fact or Fiction? Can Pathogens Survive in Beer?" Sui Generis Blog. 02/18/2014. Retrieved 11/10/2016.]</ref>. When fermenting with ''Lactobacillus'' by itself, either no alcohol is produced or not enough alcohol is produced to have an antimicrobial effect. Usually hops are not used when souring wort with ''Lactobacillus'' because even small amounts of hops completely inhibit most commercial strains, but they also inhibit some spoilage microorganisms. The high available sugars, warm temperatures typically used in souring wort, and a lack of alcohol and hops therefore increases the chances for contamination during souring wort with ''Lactobacillus''.