Quick Fermentation?

Is it possible for primary fermentation to be done in about 1 1/2 days? I put my beer in the primary on saturday afternoon at about 5pm. By Tuesday morning, there was absolutely no activity in the airlock. The bucket was kept in a dark closet and the temp was anywhere from 64 to 68 degrees.

Have you taken a gravity reading?

Airlock activity is not an indicator of finished (or started) fermentation. At that low temperature, you'll need a few weeks before it's done.

It is very possible the primary fermentation is done but the yeast is a long way from finishing its job. It takes a few weeks for it to ferment, clean up after its party, and clear your beer.

I haven't taken a gravity reading. I used vodka in the airlock and noticed that the level dropped significantly. I added a bit more vodka into the airlock (I hope this is ok?) and low and behold, it started bubbling again. I guess the yeast was still doing its job. will opening the cover to the airlock and adding more vodka cause any harm to the beer? Sorry for all the questions, I'm still very new this. This site has been such a tremendous help to me.

You should be fine opening the airlock. Because the wort puts off CO2 and it is heavier than O2, your wort essentially protects itself from oxygenation. The airlock will keep other dirt, bacteria, etc. from getting in. Might want to find out if you have a leak somewhere with your airlock. A teaspoon or so of vodka in your brew is no big deal, but you don't want to compromise your hard work if your leak is more substantial.

Good luck!

i dont think there was a leak in your airlock. chances are the air inside your carboy cooled and contracted and sucked some of the vodka into your fermenter. like Jmiltime said this is not a problem. now that fermentation is going no more vodka will be sucked back into your fermenter. chances are fermentation did not begin till some time after it sucked in the vodka.

I just did a batch of Stout, it was done in about 50 hours.
It started at 1.052 and finished at 1.020.. At least I hope its finished because I primed and bottled it this afternoon.