Wash green beans thoroughly and trim the ends.
Prepare jars by washing and keeping them warm.
In a saucepan, combine vinegar, water, and pickling salt. Bring to a boil.
Place one garlic clove, dill sprig, peppercorns, mustard seeds, and red pepper flakes (if using) into each jar.
Pack green beans vertically into jars as tightly as possible without crushing.
Pour hot brine over beans, leaving ½ inch headspace.
Remove air bubbles and wipe jar rims clean.
Apply lids and bands fingertip tight.
Process jars in a boiling water bath canner for 10 minutes (adjust for altitude if needed).
Remove jars and allow to cool undisturbed for 12–24 hours. Check seals before storing.
Store in a cool, dark place for up to 1 year. For best flavor, wait 1–2 weeks before opening.
