Wash and dry the jalapenos. Remove the stalks.
Thinly slice the jalapeños. NOTE: Remove seeds as shown in image
Combine the vinegar, water, mustard and cumin seeds, garlic, sugar and salt in a non-reactive saucepan. Over a medium heat, bring the mixture to the boil.
Add the jalapeno slices and stir. Turn off the heat. Let the mixture sit for 5 minutes.
Carefully add the jalapenos and brine into the sterilised jars. Seal the jars, and allow to cool before placing in the refrigerator.