Wash jalapenos thoroughly and slice into ⅛–¼ inch rounds. Wear gloves while handling.
Prepare jars by washing in hot soapy water and keeping them warm.
In a saucepan, combine vinegar, water, pickling salt, and sugar. Bring to a boil.
Add sliced jalapenos and simmer for 2–3 minutes to slightly soften.
Place garlic cloves, peppercorns, and oregano (if using) into each jar.
Using a funnel, pack hot jalapeno slices into jars.
Pour hot brine over peppers, leaving ½ inch headspace.
Remove air bubbles and wipe jar rims clean.
Apply lids and bands until fingertip tight.
Process jars in a boiling water bath canner for 10 minutes (adjust for altitude if needed).
Remove jars and allow to cool undisturbed for 12–24 hours.
Check seals and store in a cool, dark place for up to 1 year.
For best flavor, wait 1–2 weeks before opening.
