The bad garbage disposal smells are usually caused by food stuck on sides and blades inside the grinding chamber.
An enzyme cleaner that eats the old food material will freshen up a garbage disposal. And the enzymes will remove blockage of the kitchen pipes better than using caustic chemicals.
Safety wise, enzymes are best for clearing organic-based clogs like grease, hair, and soap with no damage septic systems. Yes, they can take 24 hours and more than one dose to work. But it’s not toxic chemicals, and it’s cleaning the source of the problem. The Zep DRAIN CARE enzymes consume the old food and sweeten a stinky disposal.
Mix 1 1/2 scoops of Zep DRAIN CARE with 20 ounces of warm water, not hot. Use a disposable container for the mixing, not a food container. Run thirty seconds of warm water into the disposal to pre-warm the surfaces. Pour the mixture into a running disposal and immediately turn it off. Do not use the sink for the rest of the night. The enzymes will coat the inside of the grinder and will eat away at the rotting food that is the source of the odor for a clean garbage disposal.
Some people try lemon peals, which helps but the stink keeps coming back within a few days. The acidic acid from the lemon does clear up some of the rotting food in the grinder, though it only reduces the odor but does not remove the rotting food.
The real beauty of this operation is the excess drain cleaner will be cleaning the lateral drain line at the same time. This is where most kitchen clogs develop, not in the disposal or the trap where most people think.