Sterilize 4 two-liter (1/2 gallon) glass mason jars.

Fill each jar 3/4 way with the cut up apples, leaving a couple inches of headspace.

In a large pot, dissolve the sugar and water. Pour over the apples, making sure they're covered completely.

Secure a clean piece of fabric or cloth over each jar. IMPORTANT: do not cover with a sealed lid, or it will explode (the fabric is breathable, allowing the gases that develop during fermentation to escape). Set the jars in a cool, dark spot for 2 to 3 weeks. Check periodically to make sure you see air bubbles begin to form at the top (good!), and that there's no mold on the apples (bad). If the apples float to the top, add something to weigh them down, and keep submerged in the liquid.

After the first round of fermenting, strain & discard the apples (it feels wasteful, I know. I added them to my compost). Pour the strained young vinegar into clean, sterilized glass jars, cover again with cloth, and let sit for 4 to 6 more weeks. Begin taste testing at 4 weeks for desired strength.

Use as you would apple cider vinegar in any recipe (including this fire cider).