Changes

During mashing, the population of microbes diminishes greatly due to near pasteurization temperatures. However, thermotolerant microbes do survive. These are usually homofermentative LAB <ref name="Bamforth">[http://mmbr.asm.org/content/77/2/157.full#ref-199 The Microbiology of Malting and Brewing. Nicholas A. Bokulicha, and Charles W. Bamforth. June 2013.]</ref>. These microbes can have both positive and negative impact on wort production. Mash acidification by thermotolerant ''L. amylovorus'' has shown to improve enzymatic conversion of starches to sugars, increased extract and fermentability, increased TSN and FAN, and even improved head retention and increased shelf stability <ref>[http://www.asbcnet.org/publications/journal/vol/abstracts/ASBCJ-63-0096.htm Biological Acidification of a Mash Containing 20% Barley Using Lactobacillus amylovorus FST 1.1: Its Effects on Wort and Beer Quality. Deirdre P. Lowe and Helge M. Ulmer. 2005.]</ref>. Bacterial growth during mashing can also have a negative impact. For example, the thermotolerant Gram-positive and facultative anaerobe ''Bacillus coagulans'' can cause the mash to go sour and has been shown to form nitrosamines in wort that was supplemented with nitrate. ''B. coagulans'' forms nitrosamines without oxygen between the temperatures of 86°F/30°C and 154°F/68°C, and can withstand a pH of 4.0 or higher <ref>[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1992.tb01124.x/pdf THE ROLE OF BACILLUS spp. IN N-NITROSAMINE FORMATION DURING WORT PRODUCTION N. A. Smith and P. Smith. 1992.]</ref>. ''Clostridium'', which may probably does not necessarily originate from the malt itself (so far studies have shown very little to no ''Clostridium'' is present on malt), can create [[Butyric Acid|butyric acid]] off flavors during the mash or during kettle souring <ref>[http://www.asbcnet.org/publications/journal/vol/abstracts/49-02.htm Butyric Acid Off-Flavors in Beer: Origins and Control. D. B. Hawthorne, R. D. Shaw, D. F. Davine, and T. E. Kavanagh, Carlton. 1991.]</ref>. High bacterial growth can cause lautering issues, probably due to the production of dextrans by the bacteria <ref name="Bamforth"></ref>.