Fill a Dutch oven three-fourths full with water; bring to a boil. Add Brussels sprouts in batches; cook, uncovered, 4 minutes or until crisp-tender. Remove with a slotted spoon and immediately drop into ice water. Drain and pat dry., Pack Brussels sprouts into six hot 1-pint jars. Divide garlic and pepper flakes among jars., In a large saucepan, bring remaining ingredients to a boil. Carefully ladle hot liquid over Brussels sprouts, leaving 1/2-in. headspace. Remove air bubbles and adjust headspace, if necessary, by adding hot mixture. Wipe rims. Center lids on jars; screw on bands until fingertip tight., Place jars into canner with simmering water, ensuring that they are completely covered with water. Bring to a boil; process for 10 minutes. Remove jars and cool.