Step 1: In a large pot, combine the apple cider vinegar, granulated sugar, turmeric, celery seed, garlic powder, and cayenne pepper. Bring the mixture to a boil over medium-high heat.
Step 2: Reduce the heat and simmer the syrup for 5 minutes to ensure all the sugar is dissolved and the spices are well-distributed.
Step 3: Add the sliced jalapeños to the pot and turn the heat back up. Bring the mixture back to a boil, then reduce heat and simmer for exactly 4 minutes.
Step 4: Using a slotted spoon, transfer the jalapeños into clean, sterile canning jars, leaving about 1 inch of headspace at the top.
Step 5: Increase the heat under the remaining syrup and bring to a hard, rolling boil for 6-8 minutes until it has thickened and reduced slightly.
Step 6: Pour the hot syrup over the jalapeños in the jars, maintaining the 1 inch of headspace. Run a clean tool around the inside of the jars to remove air bubbles.
Step 7: Wipe the rims of the jars, apply lids and bands, and process in a water bath canner for 10-15 minutes (adjust for altitude).