Prepare a boiling water canner and sterilize five pint-sized canning jars (see note). Place the lids in a small saucepan over very low heat to simmer while you prepare the green beans. Do not boil the lids.

In a medium saucepan, bring the vinegar, water and salt to a boil over medium heat. 

Place one dill sprig, 1 clove garlic, 1 teaspoon dill seed, 1/4 teaspoon red pepper flakes, 1/2 teaspoon mustard seeds and 1/4 teaspoon peppercorns in the bottom of each of the sterilized jars. Set aside.

Wash and trim the stem end of the beans so that they fit in the jar. Pack the beans into the jars, leaving 1/2 inch of headspace in the top of the jar.

Carefully pour the boiling pickling liquid over the green beans in the jars, leaving 1/2 inch of headroom between the top of the liquid and the top of the jar.

Seal with the warmed lids and rings.

Using tongs, place the jars on the rack in the boiling water canner. The water should cover the jars by at least 1 inch. Cover the canner. Return the water to a boil and boil gently for 10 minutes. 

Using tongs, transfer the jars to a towel to cool. If the seal works and fits properly, the metal lid will be slightly concave within 24 hours of processing.

Store the unopened jars at room temperature for up to 1 year. Once the jars are opened, store in the refrigerator for up to 1 month.