Calibrating mq-3's

Ok,

I've poured over the forums long enough for me to think this may be a valid question, as I can't find any straight answers...

How exactly do you calibrate a mq-3??

Yes, everyone says they're tricky to do. But no one goes into detail about the exact steps you need to take to do it.

For my project, I want to measure the alcohol content of a liquid. For example, if I take a sip of beer and promptly blow on the sensor, the mq-3 would tell me that it contains 5% alcohol, or, alternately, 40% for vodka. Also, it'd be super useful in determining if my wife is watering down the booze. :)

Any helpful souls out there willing to give me some gentle guidance?

Cheers,

Paul