If you recall the movie Back to the Future, nutty professor Dr. Emmett Brown, a.k.a. "Doc," created a time machine capable of driving back and forth in time. During one of his trips back to the future, Doc invented an automotive fuel source capable of blending and transforming fruits and veggies from a Cuisinart into a petrol equivalent. According to Doc, "The way I see it, if you're gonna build a time machine into a car, why not do it with some style?" He was probably talking more about the DeLorean sports car body, but the Cuisinart was definitely a classy feature.

The future for today
Maybe some day there'll be a plethora of time machine companies, all of which will gladly offer shares to investors to allow them to participate in jaw-dropping sales growth while also subsidizing company development costs and years of operating losses. Until that time, we'll have to settle for the developing investment craze of ethanol companies, which are capable of turning crops such as corn into an alternative fuel source -- kinda like that Cuisinart from Back to the Future.

The current craze
Part of the growing ethanol hype is yesterday's share offering of VeraSun (NYSE:VSE) to the public at $23. VeraSun is the second-largest producer of ethanol in the U.S. The company plans to use the stock proceeds to build more ethanol plants and expand market share. Imagine that. The stock opened at $28 and shot to $30 by the close of the market for a 30% gain on the day. Great Scott! No wonder investors want in on the action.

And shares of Archer Daniels Midland (NYSE:ADM) have nearly doubled this year as investors discovered it's the largest producer of ethanol in the United States. Soon-to-be-public companies include Aventine Renewable and Hawkeye Renewable. There will be no shortage of ethanol IPOs as long as investors willingly snap up the shares.

The issues with ethanol
Clearly, there are merits to producing ethanol and using it as an alternative to oil-based gasoline. It would most definitely benefit domestic farmers with a huge new market to sell corn into. It would also reduce American dependence on oil from the geopolitically charged Middle East.

On the flipside, it's unclear whether ethanol is, or will be, more affordable than gasoline. The issue is further complicated by factors such as subsidies provided to ethanol producers and fluctuating oil prices. If oil were to return to $20 a barrel, for instance, SUVs might even revisit their heyday. There's also a rather critical debate as to whether more energy is actually expended to create ethanol than is spent using it as a fuel source. And what about concerns that ethanol might damage engines and clog up filters? In other words, there are quite a few issues yet to be worked out.

Berkshire Hathaway weighs in
There's no better illustration of these issues than a summary of Charlie Munger's and Warren Buffett's thoughts on the subject at the May annual Berkshire Hathaway (NYSE:BRKa) meeting in Omaha, courtesy of fellow Fool Rick Casterline's copious note-taking.

Question: What is your opinion on the economics of ethanol as a fuel additive and as a potential investment? Should I be looking at that industry?

WB: Charlie and I don't know enough to answer that latter part. We've been approached many times, but we're trying to figure out the economics of an ethanol plant. It will depend on many factors, such as government policy and a lot of other variables we're not good at predicting. It's also a very hot area for investors right now, and our general experience is that we don't participate in things that are hot and easy to raise money for. I have a son who is head of the Ethanol Board in Nebraska. When he starts making more money than me, I'll reconsider. There's no question that usage will grow, but generally speaking, agricultural processing firms have not earned high ROICs. Look at Cargill, ADM. It has not been a great business. Ethanol could prove to be an exception, but I'm not sure how you gain a significant competitive advantage with any particular ethanol plant.

CM: My attitude is even more hostile than Warren's. I have just enough knowledge of thermodynamics left in me to suspect that it takes more fossil fuel energy than you can get out of ethanol, and that's a very stupid way to solve an energy problem. [Laughter]

The Foolish bottom line
In summary, there will be a substantial amount of money made and lost by companies and investors alike as they wrangle over ethanol and its market potential. Cynicism aside, ethanol has promise. If the economics become compelling, the industry has the potential to greatly benefit oil-dependent domestic and international economies, as well as the environment. But from an investment perspective, until that promise develops, the Foolish investor would be wise to passively watch this one unfold from the sidelines.

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Fool contributor Ryan Fuhrmann was busy buying See's candy while Rick took notes at Berkshire's meeting. He has no financial interest in any company mentioned The Fool has an ironclad disclosure policy. Feel free to email him with feedback or to discuss ethanol further. He can refer you to a number of