Clean and chop apples: If not using scraps, chop apples into small pieces. You can use peels and cores for a less waste approach. Ensure they are free from rotten spots.

Combine ingredients: Place apple pieces in a clean, large glass jar (at least 1-quart capacity). Add sugar, if using, then pour filtered water over the apples, ensuring they are fully submerged. Leave about 2-3 inches of headspace at the top of the jar.

Cover and ferment (first stage): Cover the jar opening with a breathable cloth (like cheesecloth) secured with a rubber band. This allows airflow while keeping fruit flies out. Place the jar in a dark, warm spot (65-80°F or 18-27°C) for 1-2 weeks. Stir the mixture daily with a clean, non-metallic spoon to prevent mold and ensure apples remain submerged.

Strain the apples: After 1-2 weeks, when the mixture smells vinegary and has bubbles, strain out the apple solids using a fine-mesh sieve or cheesecloth. Discard the solids.

Second fermentation: Pour the liquid back into the clean jar. Re-cover with the breathable cloth. Return it to the dark, warm spot for another 2-4 weeks. During this stage, a 'mother' culture may form – a cloudy, gelatinous disc. This is a sign of healthy fermentation and beneficial bacteria. You do not need to stir during this step.

Taste and bottle: Once the vinegar reaches your desired acidity and flavor, usually after 2-4 weeks in the second stage, remove the cloth. If a mother has formed, you can keep it to start future batches. Transfer the finished apple cider vinegar into airtight bottles and store it in a cool, dark pantry or the refrigerator.