Here are some recipes that call for vinegar.SYRUP FOR POPCORN BALLS

5 qt. corn, popped
2 c. sugar
1 1/2 c. water
1/2 c. Karo syrup
1/2 tsp. salt
1 tsp. vinegar
1 tsp. vanilla

Cook sugar, water, syrup and salt until it makes a hard
ball in water. Add vanilla and vinegar. Pour it over corn and
stir. Grease hands with oleo or wet them in water and press
into balls. This makes 20 popcorn balls.

POPCORN BALLS

1 c. light corn syrup
1 c. sugar
1/4 c. water
1 tsp. vinegar
red or green food coloring
1 Tbsp. butter or margarine
1 tsp. vanilla
8 c. popped popcorn (2 qt.)

Combine corn syrup, sugar, water and vinegar in saucepan
and enough food coloring to tint bright pink or green. Cook
over medium heat, stirring only until sugar is dissolved. Cook
syrup until candy thermometer registers 260 degrees (hard ball). Add
butter or margarine and vanilla. Pour over popcorn in large
glass mixing bowl. Stir mixture quickly with spoon or fork so
all little pieces of popcorn are coated with syrup. Butter
hands; scoop up portions of mixture. Press very lightly into
balls. Drop on wax paper. Continue working rapidly until all
mixture is used. Makes about 9 large or 18 small popcorn
balls.

POPCORN BALLS

1 c. sugar
1/4 c. Karo syrup
1/2 tsp. salt
3 qt. popcorn
1/2 c. water
1/4 c. butter
1 tsp. vinegar

Mix all but popcorn in a pot. Cook until hard ball
stage. Mix in 1 teaspoon vanilla. Pour over popcorn and mix
well. Wet hands and shape into balls. You can add 1 to 2
tablespoons molasses to make caramel popcorn balls.

POPCORN BALLS

5 qt. popped corn
1 1/2 c. sugar
1/2 c. light corn syrup
1 tsp. vinegar
1 tsp. vanilla
1/3 tsp. salt

Keep popcorn hot and crisp in slow oven (300 degrees to 325 degrees).
Cook sugar, water, salt and corn syrup to a very hard ball
stage. Add vinegar and vanilla; cook to light crack stage.
Slowly pour over popcorn; stir well to coat every kernel.
Press in balls. Use oil on hands if necessary. Makes 20
popcorn balls.