One of three ingredients in our patented, stinky, flies-love-it formula, Active Dry Yeast can be mixed with Ammonium Carbonate and water to create a brew that flies can't resist. While any substantially stinky bait will work in our fly traps, our bait is highly effective. Our pre-mixed bait is comprised of 1 oz. Ammonium Carbonate and 2 lb. Active Dry yeast. Add only water and you can make your own. Buy our pre-mixed 3 month supply or buy the ingredients separately.