13,592
edits
Changes
m
no edit summary
Pellicle formation by microbes found in sour beer such as [[Brettanomyces]] and [[Lactobacillus]] has not been closely studied. However, we may be able to glean some insight from studies done on ''Acetobacter'' pellicle formation during vinegar production.
''Acetobacter spp.'' produce homo and heteropolysaccharides (polysaccharides consisting of one type of sugar or more than one type of sugar, respectively <ref>[http://www.britannica.com/science/heteropolysaccharide Heteropolysaccharide. Encyclopedia Britannica. Retrieved 09/05/2015.]</ref>) that attach to the surface of the cells (capsular polysaccharides - '''CPS'''), as well as polysaccharides that are secreted into the medium in which they live (extracellular polysaccharides, or exopolysaccharides - '''EPS'''). The CPS is the mechanism that allows pellicle formation in ''Acetobacter'' is created by as the collection of cells tightly associated associate to one another via the CPS on the cell walls <ref name="Perumpuli"></ref>..
The exact composition of the CPS polysaccharides within ''Acetobacter'' pellicles varies between not only species of ''Acetobacter'' and another acetic acid bacteria genus called ''Gluconacetobacter'', but also strains within species. For example, ''Gluconacetobacter xylinus'' produces a homopolysaccharide pellicle consisting of cellulose, ''A. pasteurianus'' subsp. Lovaniensis produces a heteropolysaccharide pellicle consisting of glucose and rhamnose, and ''A. tropicalis'' produces a heteropolysaccharide pellicle consisting of glucose, galactose, and rhamnos. The ratios of the different sugars in heteropolysaccharides was shown to vary from strain to strain of ''A. pasteurianus''. As pellicle formation increases, the structure of the polysaccharides that make it up do not change <ref name="Perumpuli"></ref>. The fact that different species/strains use different types of sugars and different ratio or sugars for pellicle formation might partly explain some of the visual differences between pellicles.
Pellicle formation in ''Acetobacter tropicalis'' has been linked to a gene cluster (polABCDE), and disruption of these gene switched the cells from producing CPS (and pellicle formation) to producing EPS instead <ref name="Perumpuli"></ref>..
The presence of ethanol in concentrations of 1-4% encourages pellicle production in some strains of ''Acetobacter pasteurianus'' (although the presence of ethanol encourages pellicle formation, the amount of ethanol did not make a difference). In some strains of ''A. pasteurianus'', sugar encourages pellicle formation. It has been suggested that CPS production in ''Acetobacter'' is a function of stress tolerance by acting as a barrier around the cell that protects it from acetic acid in the environment. Strains that form a pellicle in the presence of ethanol and/or higher temperatures can fully ferment vinegar whereas those that do not create a pellicle perform poorly in comparison <ref name="Perumpuli"></ref>.
==Handling/Racking==