Tons of ingredients you can use.Sour wheat,corn,just about any grain..whatever is cheapest at the feed store...can even use the cheapo 50# bag of wal-mart dog food.To sour the grain,fill a 5 gallon bucket 3/4 full,add a gallon of boiling water,set in sun with a loose lid for 3 days(down wind of house)
Find a deep isolated spot in the lake near a shallow flat,or an old creek channel,start throwing about 5 pounds a day for 3 days before you are fishing.
In-fisherman had a good "How To' about 5 years ago...try a google search for catfish chumming.
Sorry I'm not Nimrod.