My method of breathing fire involves humans stomachs producing ethane or methane and them holding a lit flame near their faces and just breathing out of burping . Fire breathing in this is more cultural than useful. Humans basically worship flame it self .Is this plausible or completely ridiculous. the flame would be a very small burst
Burping is mostly caused by gas contained in the stomach. Methane and ethane are formed in the intestine by bacteria residing there.
Therefore if you want to have methane fed fire, you have to lit farts. Less epic, if you want. Or more, depending on your taste for epic.
If you want to lit burps, the only thing you can achieve is producing hydrogen using the hydrochloric acid contained in the stomach, by ingesting some metal.
But mind that hydrogen is a hell of burning gas: it easily explodes and its flames are not visible, since they emit UV.