ResearchBlogging.orgOwing to popular demand among the readership of this blog, I’ve taken a closer look at the original article claiming that spent coffee grounds can be employed as a source of fuel. There are several important details that come though in the paper coming out in the next issue of the Journal of Agricultural and Food Chemistry that have not come through in the press reports.


From the paper: Figure 1. Schematic representation of the biodiesel production process from spent coffee grounds. The other value-added products such as H2, ethanol, and fuel pellets can also be achieved from this waste feedstock.

The press reports suggest that about 340 million gallons of biodiesel can be generated using this method, which I am assuming works (or at least, I declare that I cannot tell you if their method works!). Almost nowhere is the time period over which this 340 million gallons of biodiesel would be produced mentioned in press reports or in the article, but from reading the article one gets the impression that the authors mean per year. However, that number has no support in paper itself.

Rather, there is a different, lower but more impressive number used in the paper. This is the number 2.9 million gallons per year produced by tapping only into the output of Starbucks within the United States. Worldwide Starbucks production .. taking all the used grounds from all the Starbucks in the world … would produce over 4 million gallons per year.

Total biodiesel production per year using all coffee available is estimated (the basis of the estimate not provided in any detail) to be 208 million gallons per year.

An even more interesting way of putting it is this: According to the paper, a business venture using only Starbucks coffee grounds to produce the biodiesel would yield a profit (net) of just over 8 million dollars. Now, that is based on a a fuel cost (wholesale? retail?) of $4.50 per gallon. This may or may not be realistic for a business that gets underway, say, two years from now. The total value of the worldwide industry would be a half billion dollars per year. I any event, it would seem a logical step for Starbucks to make the investment and add the production of a small amount of biodiesel to their line. Admittedly, this is not a Venti amount of fuel, not even Grande, but even a short contribution is a contribution.

It has been noted by commenters and emailers that the total production from coffee would be minimal compared to the overall demand for diesel. This, however, is not important. If we develop a hundred techniques that each operate well on a small scale and each produce one percent of need, then it does not matter that any one technique is insufficient. In fact, having a plethora of techniques has its advantages. One could cite economies of scale as a reason for monolithic approaches to production, but economies of scale are much overrated … at large scales. Such economies kick in early and peter out quickly. One could apply the same logic to individual oil wells: Since a single oil well produces only a tiny fraction of the total need, why bother? Well, because one can drill thousands of wells. And every time you add an oil well to your production, you save money on a per well basis, until some point where you are still producing a small percentage of demand. One continues to gain as one scales up because of risk reduction effects, but that also peters out and eventually is replaced by all the downsides of corporate bigness.

Presumably, one can convert dozens of good sources into biodiesel, and biodiesel can be one of many fuels. o

Compared to other sources of biodiesel, coffee grounds has a number of advantages. One is that production does not smell as bad. In fact, I would assume that production smells good, though the authors do not explicitly state this so don’t count on it. They do explicitly state that compared to using pig fat, this is better with respect to smell. This reduces cost and increases viability because those pesky quality of life regulations require that companies not build smelly biodiesel or ethanol plants just anywhere. There are other ways, chemically, in which the oil extracted from the coffee grounds is better than other sources of oil.

And, getting back to the issue of quantities of production, the data supplied in this paper indicates that a large scale production from coffee grounds would be in the same approximate order of magnitude of production from other sources such as chicken fat. Also, coffee based biodiesel is also more stable than some other biodiesel sources.

Finally, there are outputs from the process that can be fed into ethanol production or used as fuel pellets.

The bad news is not mentioned anywhere: If you can make biodiesel out of coffee grounds, than certainly you can make it out of the coffee before making the beverage. Indeed, you’d get a lot more fuel if you skipped the part about making the Cappuccino or Latte. The employment of coffee as a fuel may be too expensive right now, but if fuel prices ever rose sufficiently in relation to over the counter beverage prices, or if a major controlling agency simply co-opted the coffee for fuel, it is conceivable that there would be a coffee shortage (for drinking coffee) because its use in cars and trucks would be muscling out beverage related application.

If that happens, civilization will end shortly thereafter. So let’s not do that, OK?

Kondamudi, NarasimharaoMohapatra, Susanta, Misra, Mano (2008). Spent Coffee Grounds as a Versatile Source of Green Energy Agicultural and Food Chemistry


  1. #1 Dunc
    December 16, 2008

    My earlier comment about how this stacks up against total demand was not intended to dismiss the idea, merely to place it in context.

  2. #2 Jim Lund
    December 16, 2008

    A coffee-based means of generating energy suffers from the problem identified in the Monty Python ‘String’ sketch.

    In that sketch, a man with a lot of string he wants to market has the problem that, due to poor planning, it has all been cut into two inch lengths…

  3. #3 T. Bruce McNeely
    December 16, 2008

    My coffee IS diesel.

  4. #4 John McKay
    December 16, 2008

    Would we get a choice of caf or decaf diesel?

  5. #5 Tony P
    December 16, 2008

    I don’t think the 2″ string analogy applies here. I’ve noticed that in more and more workplaces the instant coffee machines are popping up. Those are the ones where you pop in a small cup cartridge, put your cup underneath and press the brew button and in a short time you have a cup of fresh coffee.

    Why not couple up with them, give people a break on the coffee cartridges for recycling them.

  6. #6 Anthony
    December 16, 2008

    The real problem with converting coffee waste to fuel is that you can compost it instead, and probably save more oil (by preventing the consumption of oil for fertilizer) than you would produce by processing the biomass. The advantage to converting things like chicken guts to oil is that meat byproducts are a biohazard.

    An interesting thought about biofuels: the reason biofuels are carbon-neutral is because they take in CO2 when growing, which is then released when they are burnt. However, there’s no technical reason the it has to be the same carbon — you can just as well plant crops, bury the results, and burn fossil oil. You just have to make sure that the carbon doesn’t get back into the atmosphere (bury it in a subduction zone?)

  7. #7 Greg Laden
    December 16, 2008

    Anthony: No, you put the carbon (which could be sewage even) into exhausted petroleum extraction areas. Then later it is easier to get it back. As petroleum.

  8. #8 Office Coffee Machines
    December 17, 2008

    There is very little organic material lost when you extract a cup of coffee. 1 kg of coffee (around 100 cups) will yield not much less than 1kg of coffee grounds.

    Like everything the retrieval of the coffee grounds in a cost effective manner will be the tricky part to making this economically viable. Maybe that’s where the office coffee services will play a role.

  9. #9 Coffee Machines
    December 17, 2008

    I think the days of those Coffee Pods you refer to which have the gound coffee in a small plastic capsule will not be long lived and Ground Beans will always represent the large bulk of roasted coffee representing a great opportunity to recyle from Coffee Shops, cafes and Offices

  10. #10 Jet
    December 17, 2008

    wow, this is cool.. coffee for creating fuels. well, i love coffee… who about these guys?

  11. #11 Commercial Coffee Machine
    November 29, 2009

    Just goes to show, coffee is the perfect solution to any situation; even as an energy source šŸ˜›