Use the tip of a sharp knife to split the vanilla beans down the middle, length-wise.
Add the vanilla beans to the bottle. Trim the beans if they pass the bottleneck and add the short pieces back to the bottle.
Pour the vodka or glycerin over the vanilla beans until they are covered, or the bottle is nearly full.
Screw on the lid tightly and apply a label. Include the date produced and the type of liquid used.
Let the vanilla extract steep in a cool, dark place for at least six weeks but preferably 6 to 12 months for the best flavor. Gently shake the jar once a week.
Notes
By law, spirits should contain at least 35% alcohol per volume (or 70-proof). I used Svedka Vodka and Wray and Nephew White Overproof Rum.
Ensure the jars you plan to use are taller than the vanilla beans. Sterilize and dry the jars before making the extract.
To sterilize jars, add them to a large pot of water. Ensure they're completely submerged and boil for at least 10 minutes. Sterilize the lids for 10 minutes in gently simmering water. Place them on a clean cooling rack upside down and allow them to dry thoroughly.
The longer the extract sits, the richer in flavor it becomes. Steep for up to a year for even more flavor.
Alcohol-based vanilla extract can be replenished as it is used but may require a bit more steeping as the flavor will be more diluted.
The vanilla extract made with an alcoholic base will enjoy a typical shelf-life of 4 to 6 years. The glycerin-based extract has a shelf life of 1 year.