Thoroughly wash the entire pineapple, scrubbing the skin well. Peel the pineapple, retaining only the skin and any leftover core pieces. Cut the pineapple skin into smaller pieces, ensuring they are clean.

In a large glass jar or food-grade bucket (at least 1.5-gallon capacity), combine the pineapple skin pieces, filtered water, brown sugar, and optional cinnamon stick. Stir well until the sugar is fully dissolved.

Cover the opening of the jar with a breathable cloth (like cheesecloth or a coffee filter) secured with a rubber band. This allows air circulation while keeping fruit flies out.

Place the jar in a warm spot away from direct sunlight, ideally between 68-78°F (20-26°C). Allow it to ferment for 24 to 72 hours. Check it periodically; small bubbles will start to form, indicating fermentation.

Taste the tea after 24 hours and every 12-24 hours thereafter. The longer it ferments, the tangier and less sweet it will become, and the more alcoholic it can get. Stop fermentation when it reaches your desired taste.

Once fermented to your liking, strain the liquid through a fine-mesh sieve into clean bottles or jars, discarding the solids. For a clearer tea, you can strain it again through cheesecloth.

Store the fermented pineapple skin tea in the refrigerator. It can be enjoyed immediately and will last for about 5-7 days. Serve chilled.