I cut most of the beef out of my diet about two years ago; that said, I'll admit that I still have a weakness for the occasional steak. And on the subject of steak, I recently found out something cool about biofuels and animal feed.
Animal feed supply is one of the biggest industries in the United States. Two of the biggest sources of animal feed, particularly for slaughter cattle, are DDGS (dried distiller's grains and solubles) and soy flour. DDGS is the dried byproduct of fermentation from grains, these days typically ethanol but including some beer manufacturers. It's such a huge source of feed that some ranches are now relocating to be near ethanol plants to take advantage of wet distiller's grains (WDG), which have a shorter shelf life but are cheaper since they don't need to be dried.
Soy flour is the other main source of feed; a tiny, TINY proportion of commercially grown soybeans goes to people. The remainder is crushed for its oil, with some having protein extracted by hexane washing, and is toasted and fed to cows. But powdered soy flour isn't directly edible, so typically a feedlot will add a humectant - a moisturizing agent - to make it possible for cows to eat.
Over the past 50 years, this was typically yellow grease. Yellow grease is nasty stuff - it's essentially what comes out of the frialator at restaurants. Most food outlets pay for their used oil to be disposed of by professional retrieval companies, which then sell it on the market. In recent years, yellow grease prices have gone up because it turns out it's an excellent feedstock for biodiesel. Well, not so excellent, since it's got catalyst poison making up 50% of its mass, but there are ways to get around that (no joke). Point is, it's cheaper than virgin oil by a lot, so the biodiesel manufacturers that are smart have equipped themselves to deal with this heavy feedstock.
At first, feedlot owners weren't too happy about that. But recently, feedlot owners have discovered that raw glycerin, a byproduct of the biodiesel process that contains about 50% water, lots of glycerin, and other contaminants, can be relatively cheaply processed without glycerin concentration - the energy-intensive step - to be a humectant for soy flour. And get this - turns out the cows like it even better, and it's cheaper than yellow grease anyway. The biodiesel manufacturers I talked to are currently giving it away for five and a half cents a gallon.
Considering I spent a good two years of my time at MIT trying to find a home for raw glycerin, this makes me very happy. Also it's great not to have my ribeye cut contain recycled Mickey D's. But more importantly, it's now providing an important secondary revenue source for biodiesel manufacturers, letting more of them continue producing even when diesel prices are low.