Wearing gloves, slice off the stems from the peppers, then slice into 1/4-inch thick rounds. Transfer to a bowl and set aside.
In a large pot over high heat, combine apple cider vinegar, granulated sugar, brown sugar, turmeric, garlic powder, celery seed, and cayenne pepper. Bring to a boil, then reduce heat and simmer for about 5 minutes.
Add the sliced jalapeños, bring back to high heat, and simmer for exactly 4 minutes.
Use a slotted spoon to transfer the peppers into clean, sterile canning jars, leaving about a 1/4-inch space from the top.
Increase the pot’s heat to high and boil the liquid for about 6-7 minutes. Remove from heat and let cool for 3 minutes.
Carefully pour the syrup into the jars, ensuring jalapeños are submerged. Use a chopstick to release any air bubbles.
Wipe jar rims with a damp paper towel, seal with lids, and refrigerate.
Chill for at least 2 weeks (a month is preferable) for the best flavor.
Keep stored in the fridge and consume within 2 months.