CSL - Corn Steep Liquor is a products of the processing of maize. It has concentrated nutrients, both carbohydrate and protein.
One of the largest uses for CSL is in the field of biotecnology where for years, it has has been used as a substrate in the fermentation of antibiotics, amino acids and citric acid.
It is extremely cheap.
You can buy the stuff from maize processors at a ridiculously low price. I guess that's why some of the bait and pellet suppliers are making a fortune.
Food for thought. innit?