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inserted link for microscope
# The number and size of bubbles in a pellicle is largely dependent on the amount of trapped CO2, and thus is not an identifying feature.
# The factors that cause pellicle formation are not well understood. Oxygen is said to cause pellicle formation, but how, why, and in what species is not known. Does more oxygen create a thicker pellicle? If so, for what species does this apply to? Does beer composition (more or less protein content, residual sugars, etc.) affect pellicle appearance? The lack of answers to these questions and others imply that environmental factors are also not helpful in identifying what species of microbe produced a pellicle.
# Identification of microbe species and sometimes even genus under a [[Microscope|microscope ]] based on cell morphology alone is not enough to be certain of that identification (see [http://suigenerisbrewing.blogspot.com/2014/12/brett-trois-riddle-wrapped-in-mystery.html this article on Trois identification] as an example), let alone attempting to identify microbes based on a visual "macro-level" formation such as a pellicle.
# DNA analysis of a microbe is the only way to reliably identify the species of a microbe. This is why [http://bootlegbiology.com/2015/09/17/local-yeast-project-study-barrel-culture-t-shirts/ Bootleg Biology is launching a program to identify wild caught microbes through DNA analysis].