Clean beans thoroughly; drain and pack into 7 sterilized pint jars. Into each jar, put 0.125 teaspoon cayenne pepper, half teaspoon mustard seed, 1 head dill, and 1 clove garlic. Combine vinegar, water, and salt; bring to a boil; Pour boiling liquid over beans, leaving 1 cm headspace. Wipe rims with a damp cloth. Remove air bubbles. Seal according to lid manufacturer's instructions. Process in a boiling water bath for 10 minutes. Make 7 pints.