Place the produce scraps in the base of your jar and add the water (if using a soda bottle, puree the scraps and filtered water in a blender to make a fine slurry that can be poured into the bottle. If you need to add more water to make it pourable, that's fine.)
Add the yeast and brown sugar.
Screw on the lid and give it a good shake to mix everything together. Place in a warm, dark cabinet to ferment.
Once or twice a day, shake the mixture and unscrew the lid to release any built-up pressure inside the jar. If you don't, eventually your jar could explode, so it's best to keep an eye on things.
After 4 weeks, strain the liquid into a glass spray bottle. Wrap the solid scraps in a piece of cheesecloth and squeeze it to get any lingering enzymes.