In a medium-sized, non-ionized pot combine balsamic vinegar, water, sugar, soy sauce, thyme, and mustard seeds.

Cook on low-medium heat until sugar is completely dissolved. Remove from heat and allow to cool to room temperature (to avoid mushy strawberries).

Divide prepared strawberries between jars. Cover strawberries with vinegar brine (plus thyme and mustard seeds).

Wipe rims and apply lids. Place in refrigerator for at least 12 hours before consuming.