Wash and sterilize the bottles that will be used. (See Tip 3)
With a sharp paring knife cut the vanilla beans down the middle. Place the beans in the clean bottle. Pour in vodka. Seal the bottle, and store in a cool, dark place. Let the vanilla extract age for at least 8-weeks before using, occasionally shaking the bottle. (See Tip 4)
Note: When the vanilla extract gets low, add more vodka to the bottle.
Tips/Notes
It's important to use unflavored vodka. Also, you don't need to use an expensive vodka. If desired, you could use bourbon, rum or brandy in place of the vodka.
I like to use Madagascar Bourbon Grade-A vanilla beans. My rule of thumb is to use 5 to 6 per 8 ounces of liquid.
If you're using swing-top bottles, it's best not to put them in the dish washer. The reason is that the metal for the swing-top could corrode.
The longer the vanilla beans infuse, the better. I like to wait at least 5 months.