Butter sides of a very large bowl that is holding your popcorn, the mixture will be quite sticky and you do not want the sugar mixture to stick to the bowl.
Butter sides of a large saucepan.
Half fill a small bowl with water.
This will be used to dip your hands in to form the hot popcorn mixture and prevents it from sticking to your hands.
Attach a good candy thermometer to the side of your saucepan.
In saucepan combine the sugar, water, salt, corn syrup and vinegar.
Cook over medium heat until the thermometer reaches 250 degrees or the hard ball stage.
This takes quite a bit of time, but please, do not walk away from your saucepan.
Stir it regularly and watch closely.
Once it reaches the hard ball stage, turn off the heat and add your vanilla.
Pour hot mixture over the popped popcorn, stirring to mix well.
Dip hands in water bowl and then form popcorn into balls.
You need to work quickly for the sugar mixture once it starts cooling will harden.
Shape into balls and place balls onto a parchment lined baking sheet.
This made 16 XL popcorn balls for me.
**WARNING!
These balls are very addictive and are also very, very sticky!