Changes

Bokulich et al. (2015) studied the microbial populations throughout a brewery (presumably Allagash) that produces clean beer, mixed fermentation sour beer, and spontaneously fermented coolship ale. They found that most of the microbes living in breweries were introduced from the ingredients such as malted barley and hops, and many populations were confined to specific rooms or areas within the brewery. Some species did spread to other rooms, presumably through human and insect vectors. Beer resistant lactic acid bacteria spread throughout the brewery (although more abundantly found near packaging equipment and fermenters that were filled with sour beer), but the clean beer was largely uncontaminated. Physical partitions and walls appeared to help inhibit the spread of microbes from room to room<ref name="Bokulich_2015">[https://elifesciences.org/articles/04634 Mapping microbial ecosystems and spoilage-gene flow in breweries highlights patterns of contamination and resistance. Nicholas A Bokulich, Jordyn Bergsveinson, Barry Ziola, David A Mills. 2015.]</ref>.

Ale yeast was found throughout the brewery, especially in the fermentation cellar. Malted grains were determined to be the highest source of potentially contaminating microbes (mostly ''Pediococcus'', although the PCR method used in the study was not adequate for detecting microbes on grain) in the hotside areas of the brewery compared to other microbe sources such as human skin, outdoor air, soil, saliva, feces, water from the plumbing, etc. Hops were determined to be the highest source of microbes in the cellar fermentation areas (''Pediococcus'' spp, ''Lactobacillus lindneri'', and ''L. brevis'' were detected on pellet hops, although the presence of hop tolerant genes was not detected from microbes found on hops), and yeast was the highest population in fermenter and packaging areas. While human skin was a minor contributor to microbe populations found in the brewery, oak barrel surfaces were populated with microbes from unknown sources. Therefore, it was determined in this study that raw materials are the major source for potential contaminants in a brewery, although minor sources such as sinks are still potential problems and hop tolerant species were linked to the purposeful inoculation of souring microbes in the sour beer production itself<ref name="Bokulich_2015" />. ''L. lindneri'' is highly hop tolerant, difficult to detect on MRS media, and has been found to survive suboptimal heat pasteurization temperatures. ''L. brevis'' strains that have been growing in beer are also hop tolerant, although some strains have been found to lose their ability to grow in beer if they are grown in lab media after a few generations and strains not found in breweries are not hop tolerant, which suggests that strains found in beer have adapted to that environment. Both of these species also have a smaller cell size when they have been growing in beer, and can pass through microbial filtration systems <ref name="Suzuki_2012">[https://onlinelibrary.wiley.com/doi/abs/10.1002/j.2050-0416.2011.tb00454.x 125th Anniversary Review: Microbiological Instability of Beer Caused by Spoilage Bacteria. Ken Suzuki. 2012. DOI: https://doi.org/10.1002/j.2050-0416.2011.tb00454.x]</ref>.

Seasonality played a minor role in the populations of microbes throughout the brewery, with ale yeast and ''Candida santamariae'' spreading from the fermentation and packaging area to the rest of the brewery from fall to summer (it was proposed that the warming from fall to summer played a role in the spread of ale yeast and ''Candida santamariae'' throughout the brewery). ''Micrococcus'' and ''Kocuria'' were found in more localized areas such as the floors and other surfaces in the barrel room, cellar, and packaging room. ''Acetobacter'' and ''Lactobacillus'' were found specifically in areas where a lot of wort or beer was being processed (conveyor belts and floors below the packaging equipment, hotside and cellar area sinks, and sample ports on kegs and fermenters). ''Lactobacillus'' was more common on surfaces where sour beer production was (fermenters and barrel surfaces), with floor surfaces having a more diverse mixture of LAB species<ref name="Bokulich_2015" />.

Microbes with hop tolerant genes were found more abundantly in the fermenter and packaging areas (filler heads, below the bottling line belt, packaging sink, and a keg faucet) compared to microbes found on pellet hops (which were determined to not be a source of contamination), kegs, or barrel bungs, and was associated with where beer was being processed, particularly mixed fermentation and spontaneously fermented sour beer <refname="Bokulich_2015" />[https://elifesciences.org/articles/04634 Mapping microbial ecosystems  In the case of mixed cultures or contaminations that contain ''Pediococcus damnosus''., ''Lactobacillus brevis'', or ''Lactobacillus lindneri'', and spoilage-gene flow possibly other species of these two genera, it is possible for the cells of these bacteria to adhere to the cells of brewers yeast. This can cause the yeast to prematurely drop out of suspension during fermentation, resulting in breweries highlights patterns under attenuated beer. This function of contamination and resistancethe bacteria is thought to contribute to the slower development of the bacteria after the yeast has dropped out of solution. Nicholas A Bokulich, Jordyn BergsveinsonOther species of ''Lactobacillus'' such as ''L. casei/paracasei'', Barry Ziola, David A Mills''L. 2015coryniformis'' and ''L.]plantarum'' as well as species of ''Leuconostoc'' are very intolerant of hops and are therefore only considered a threat against beer that is very lowly hopped <ref name="Suzuki_2012" /ref>.