Re: What is the black on the bottom of the container and the film on the top ?

It would be impossible to determine whether or not bacteria are present in 
the film you describe simply by the appearance. You may, in fact, have a 
biofilm or "sheet" of bacteria linked together but you would have to send 
a sample to a microbiology testing lab for analysis in order to make this 
determination. It is likely that you have a combination of fats and 
bacteria.