Make Pickling Spice by combining the black peppercorns, mustard seeds, coriander seeds, dill seed, crushed red pepper flakes, and optional allspice and bay leaves in a mixing bowl.

Prepare jars by sterilizing them in the dishwasher or boiling them in water for 10 minutes.

Prepare brine by combining equal parts apple cider vinegar, white vinegar, water, and pickling salt in a stockpot. Simmer for 5-7 minutes.

Assemble jars by adding pickling spice mix, sprigs of fresh dill, sliced Thai red peppers, and minced garlic cloves to each jar, followed by packing the cucumbers.

Pour hot brine over the ingredients until just below the rim of the jar, leaving half an inch of headspace.

Seal jars by wiping rims and placing sterilized lids on top, then process in a boiling water bath for 10 minutes.

Cool and store jars for at least 24 hours, checking that the lids have sealed properly before storing in a cool, dark place.