Ok, so I have an on-going joke with my co-workers as to the chemical equation of a "fart". I personally have been making up something that isn't even remotely close to the chemical equation.
I'm sure it has a lot to deal with what you ate. However, your gastrointestinal tract has to have some sort of chemical breakdown.
In your closest guestimation: What is the chemical equation of a "fart"?