Distillers Grains

What is a "Distillers Grain"? 
Distillers grains are cereal by-products of the distillation process - distillation for Biodiesel or Brewing (for alcohol or alcoholic beverages). 
What's the process of making a Distillers Grain?
Using the popular grain Corn we'll walk through the process. First its sent to biodiesel as corn.  It is then fermented to separate the starch ("Liquid Energy") from the protein (trash that they can do nothing with). Fermentation naturally produces Amino Acids and B-Vitamins... thus making any product that uses Distillers Grains likely higher in Amino Acids and B-Vitamins (as validated in KYPF testing). 
In addition to fermentation, Distillers Grains may contain some or all of the following ingredients:
- Alpha and Gluco-Amylase (enzymes that separate starch from protein, for ethanol production)
- Cream Yeast and Yeast Vitamins (Also for starch extraction, increases B-Vitamins)
- Antibiotics (Tylosin, Virginiamycin, Erythromycin) (prevents aflatoxins)
- Sulfur & Chlorine Dioxide (Corrosive, dangerous chemical. Classified by the EPA as toxic at levels as low as 2ppm. Corn Gluten Meal has tested with levels of Sulfur Dioxide as high as 280ppm. Distillers grains are soaked in Sulfur Dioxide for up to 40 hours prior to being sent to pet or agricultural feed. Distillers Grains and legally classified by the EPA as "chemicals," not food) (Corn Gluten Meals Chemical ID - Toxic Substances Control Act of 1990 8(8) - 5.6+ million tons produced for the US annually)
- Liquid Urea (Stated in its MSDS to cause cancer and reproductive harm)
- Diammonium Phosphate (linked to some blood and liver diseases)
- Annhydrous Ammonia (pH stabilizer and fertilizer. May cause severe corrosion of digestive and respiratory lining - likely injurious to pet food manufacturer employees as it off-gasses during heating.) 
- Proprietary Enzymes
- Corn Steep Liquor (used in Petri dishes to grow bacteria - thus increasing risk of bacterial proliferation in Distillers Grains ingredients that contain this component)
Differences between Corn Meal (food) and Corn Gluten Meal (Distillers Grain from Biodiesel):
- Distillers grains have DECREASED levels (from low to high nutrient losses) of Alanine, Aspartic Acid, Cysteine, Glutamic Acid, Histidine, Isoleucine, Methionine, Proline, Serine, Threonine, Valine, Folate, Fat, Arginine, Glycine, Lysine, Tryptophan, Iron, Copper, Fiber, Carbohydrates, Linoleic Acid, Stearic Acid, Sodium, Zinc, Manganese, Oleic Acid, Magnesium, Calcium, Phosphorus, Potassium
Distillers Grains are higher in Protein than their original counterparts (e.g. Corn Gluten Meal is higher in protein than Corn Meal) because the starch has been extracted and the high protein "trash" is sent to pet food. 
So you can get higher protein ingredients from Purina ProPlan's distillers grains than you can from Taste of the Wild's potatoes... but in conjunction, you get a bunch of chemicals. The chemical and heat processing, though, can damage the remaining nutrients. Some nutrient levels actually INCREASE in this process.
How would a Distillers Grain be listed on an ingredient panel? Potentially... 
Any derivative of Corn or Corn Gluten Meal,
Any derivative of Rice or Brewer's Rice,
Any derivative of Soy,
Any derivative of Potato
Any derivative of Mustard Seed,
Any derivative of any any base ingredient used to make hard liquor
Grains, in their natural state, contain the same levels of antinutrients but generally less protein than grain alternatives. As seen in KnowYourPetFood.org testing, kibble products that contain distillers grains contain the same antinutrient levels as grain free products. It is therefore a lateral move to feed a high-heat processing grain containing or grain free product. (Carna4 is the one exception - as they are low heat cooked and they sprout their base)
If you are attempting to increase your pets protein or amino acid content (to prevent or resolve heart disease, cachexia, tissue damage, etc) you will get more amino acids and fewer toxins from quality meat sources. Minimally processed ORGANS are the best source of amino acids and minerals (see NutritionData.com for details).