From The Great Transition, (c)2014, by Lester R. Brown (preface, page xiii):

[F]illing the tank of a large SUV one time with ethanol takes as much grain as could feed a person for a whole year.

Since it definitely costs me more in a year to eat than it would to fill the tank of an SUV, something must be off here. What am I missing?

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    I suspect your food budget is a wee bit over US$100 per person per year. That figure is in line with impoverished areas of the third world. – David Hammen Aug 6 '18 at 2:17
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    I seriously doubt that the above takes the fact that not all crops are fit for human consumption into account. You can still make fuel alcohol from the portion of the crop that would otherwise be rejected, or from the inedible portions like the cob – GordonM Aug 6 '18 at 9:45
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    @GordonM It's theoretically possible to make ethanol form the cob, but that's not how it is done in practice. The cobs are usually left in the field in US practice. – DavePhD Aug 6 '18 at 12:32
  • If you're making ethanol yourself you can make it from almost anything containing sugar or certain starches. Waste food can be used. Pure Ethanol can be chemically synthesized using petrochemicals also. But I'm guessing this is about the relative cost of gasoline Vs distilled ethanol. In any situation you can imagine.. it is cheaper to create fuel from oil. Partially because of economics favouring that, but mainly because oil is abundant, energy rich and easy to process. With current technology there is nothing to compete. Until viable fusion, or much more efficient solar power.. – Richard Aug 6 '18 at 22:51

Mathematically accurate

From Cornell University News:

An acre of U.S. corn yields about 7,110 pounds of corn for processing into 328 gallons of ethanol.

That's 3,225 kg and 1241 liters.

Let's assume that the "large SUV" has a twenty gallon (76 litre) tank. So that's 7110 pounds divided by about 16. That comes out to 433 pounds (196 kg) of corn.

From the Washington Post:

[...] each pound of corn yields about 1,566 calories.

That's .45kg and 6.56 MJ.

Multiplying by 1566 and dividing by 365 gives us about 1860 calories (7.8 MJ). That's sufficient calories per day for a sedentary forty year old woman (as per WebMD). If our large SUV instead had a thirty gallon (114 litre) tank, that would bring things up to around 2790 calories (11.7 MJ), enough for a moderately active man.

This obviously ignores any nutritional deficiencies in corn. In reality an all corn diet would likely be short on some key nutrients, like protein. But given that caveat, the comparison is numerically accurate.

Why it seems off

Since it definitely costs me more in a year to eat than it would to fill the tank of an SUV, something must be off here. What am I missing?

I don't know your actual shopping and dietary habits, but I suspect:

  1. You don't buy corn in bulk from farmers. As such, if you bought 433 pounds (196 kg) of corn, you'd pay more than the $21 (US; see the Cornell link for the $1.05 per gallon price).
  2. You have higher standards for your corn than ethanol producers do.

    • You want your corn juicy, not dry.
    • You want all of the husk removed, including the silk strands.
    • You want all of the cob removed.

    Ethanol producers don't care as much about that stuff. Corn is preferable, but it's not like they're eating it. So processing corn for ethanol can take shortcuts that food processors can't.

  3. Food corn that is not perfect is removed and not sold as food for people. It may be fed to animals or turned into ethanol.
  4. A lot of the food that you eat is more expensive than corn. Corn is a staple crop. It's one of the cheapest foods around. You'd pay a lot more for a steak made from a cow (probably fed with corn). But even a decent vegan diet is going to cost more than corn does. It's not like you eat raw soybeans, corn, wheat, oatmeal, and various vegetables. You typically add spices, sweeteners, etc. as well as the cost of preparation.
  5. On average, your food probably travels farther than corn does to become ethanol. This is because the ethanol producers can locate close to the corn to save on shipping costs. And they don't need their corn fresh. Some of your food probably comes from the other side of the equator, where it is freshly grown and shipped quickly to you.
  6. You probably spend a significant amount of your food budget on packaging and preservation rather than the contents. You can get a bushel (25.4 kg) of corn for about $1, but that might buy you a small bag of frozen corn.

TL;DR: you likely have a more expensive diet than just corn bought in bulk directly from the farmer.

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    I would use a 33.5 gallon tank (Lincoln Navigator L). The (apparently biased) link is almost certainly going to use the SUV with largest possible tank for this comparison; you should do the same. That eating a diet consisting of corn and corn only would almost certainly result in a fairly quick and rather painful death (e.g., scurvy) is of course completely irrelevant. – David Hammen Aug 6 '18 at 2:23
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    But 'gasahol' as sold at the pump is usually 10% ethanol- so your 33 gallon tank would take 3.3 gallons of ethanol. According to one source (HowStuffWorks) 26.1 pounds (11.84 kg) of corn goes into one gallon of ethanol, so figure ~85 pounds of corn. This could conceivably feed an individual for most of a year, when part of a balanced diet. – BobT Aug 6 '18 at 2:52
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    @BobT Surely the claim is talking about engines running on pure ethanol? – gerrit Aug 6 '18 at 11:04
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    Brythan, normally only the pure corn kernels are collected upon harvest, like this youtube.com/watch?v=m1BaQQKE6Ts The combine removes all the kernels from the cobs. All corn weights and volumes refer to the pure kernels. – DavePhD Aug 6 '18 at 12:14
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    I call BS. I never said that ethanol producers buy the whole cob. I said that ethanol producers don't care as much if the corn is dirty or contaminated. And while people occasionally buy the whole cob, it is far more common for people to buy corn frozen or canned. Regardless, since people don't eat the cob, the cob doesn't increase the calories. It may increase the cost, as it is more weight and volume to transport. Why is it so important to misinterpret what I said? I'm comparing food-grade kernels to ethanol-grade kernels. When you misunderstood, I clarified. Why double down? – Brythan Aug 6 '18 at 13:18

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