Using a long, sharp knife, slice off the bottom of the pineapple, cut off the top, then cut off the thick outer layer. (See note #1)
Lay the pineapple on its side, slice it, remove the peel, and chop the pineapple flesh into chunks.
Next, add the chunks to a food processor or blender, together with water and sugar (if using).
Blend until a smooth puree with no chunks of fruit in the mix.
Strain the juice using a fine sieve or cheesecloth. Be sure to press out all the juice from the cheesecloth.
Adjust the taste and thickness of your juice with more water or sweetener.
Serve immediately with ice cubes, and garnish with pineapple, lemon, or mint.