First, fermentation can take up to 72 hours for the yeasties to start, it's called lag time. http://www.homebrewtalk.com/f39/fermentation-can-take-24-72-hrs-show-visible-signs-43635/
But by visible signs they DON'T mean airlock activity.
Your airlock is not a fermentation gauge, it is a VALVE to release excess co2.
If your airlock was bubbling and stopped---It doesn't mean fermentation has stopped.
If you airlock isn't bubbling, it doesn't mean your fermentation hasn't started....
If your airlock starts bubbling, it really doesn't matter.
If your airlock NEVER bubbles, it doesn't mean anything is wrong or right.
The only way to truly know what is going on in your fermenter is with your hydrometer. Like I said here in my blog, which I encourage you to read, Think evaluation before action you sure as HELL wouldn't want a doctor to start cutting on you unless he used the proper diagnostic instuments like x-rays first, right? You wouldn't want him to just take a look in your eyes briefly and say "I'm cutting into your chest first thing in the morning." You would want them to use the right diagnostic tools before the slice and dice, right? You'd cry malpractice, I would hope, if they didn't say they were sending you for an MRI and other things before going in....
Thinking about "doing anything" without taking a hydrometer reading is tantamount to the doctor deciding to cut you open without running any diagnostic tests....Taking one look at you and saying, "Yeah I'm going in." You would really want the doctor to use all means to properly diagnose what's going on. It's exactly the same thing when you try to go by airlock....
You'll be much happier if you get out of that habit...you will find that fermentations rarely don't take off, or just Stop...In fact I've never had a beer not ferment. BUT half of my fermentations, spread out across 9 different fermenters, never blip once in the airlock.
Fermentation is not always "dynamic," just because you don't SEE anything happening, doesn't mean that any-thing's wrong,, and also doesn't mean that the yeast are still not working diligently away, doing what they've been doing for over 4,000 years..
So, Relax, then wait 72 hours and take a hydrometer, and you'll see, more than likely that everything is fin...it is fine 99.95% of the time.
And read this as well, Why the idea of "dead yeast" is mostly bunk.
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