So as a teen my room gets very messy and things get forgotten to be disposed of. Four days ago I was looking at an old glass bottle that had been sealed (though probably not air tight) with about 1in of liquid Pepsi in it when measured from the bottom. I saw that a thin barely visable whiteish structure had formed. After lightly swishing the bottle the structure had held together. Today the structure spans a spot of about 1 square inch on the surface of the Pepsi and is now clearly white. So what could this thing be? At first I thought it was sugar crystalizing, but that would happen on the sides. Right? Could it be a bacteria? I know they can grow on dried Pepsi, But I've never heard of some growing on liquid Pepsi.

Thanks for the help.
Sincerely,
Jacob C Phelps

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G'Day Jacob: While I don’t know what is growing in your beverage my guess would be that it is a mold (which can grow as white, fluffy masses) or yeast rather than bacteria. These soft drinks have a high concentration of sugar that many bacteria don’t like (although some strains of staph love it!), and at least for a while the beverage is/was probably acidic. Some yeast, molds or bacteria (e.g., acidophiles) would likely enjoy this environment but most would not. 

I imagine once the beverage dries however all sorts of bugs could thrive in it.

see also - http://www.bcnlabs.com/beverages