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I was given a few packs of grain coffee. The smell was pretty nice and it was written that it's 100% arabica. That encouraged me to grind some and brew it in moka pot.

The result I got was not horrible, but way to sour for me. I tried one bean and indeed it was little sour, compared to Starbucks Espresso Roast, which is not sour at all and has great almost black color.

I am sure this will not be my coffee of choice, but it would be nice to upgrade it somehow (before I throw it away), though I have no idea how to do it. I thought about roasting it in the oven (210-225 Celsius; 410-437 Fahrenheit) for 10 minutes.

Do you think it might be a good idea?

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    I think your question isn't so much about the possibility of re-roasting beans, but how to improve the taste, so I suggested an edit to the question title.
    – lemontwist
    Dec 25, 2012 at 13:45
  • very alkaline water? would creating a salt (acid+base) be as bad?
    – Pat Sommer
    Dec 27, 2012 at 0:14

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Yes, you can roast the beans some more. However the results will probably not be great.

Roasting results in quite a bit of smoke. If you are going low tech, I would do it in a wok in a very well ventilated area. It's pretty easy to set off smoke detectors. A stove top with a range hood might be good enough if you have a particularly good range hood. Outside with the wok on a BBQ is probably best.

Roast over a low heat and stir continuously. You want to get the beans as even as possible, trying not to burn them. The beans will continue to roast after taking them off the heat. So stop one or two roast levels before the desired colour and tip your beans out into a colander and continue stirring to cool. The residual heat will cook the bean some more.

To aim for a desired roast level, compare the current roast colour to your desired roast colour and maybe to a roast level chart. Google image search "coffee roast level chart". Guesstimate the roast level that is one or two levels below your desired colour to stop at.

Once again there will be a lot of smoke.

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    But will this make the coffee less sour?
    – rumtscho ♦
    Dec 25, 2012 at 15:16
  • Hard to say without knowing what the bean is. But as you take the roast darker, you tend to get more caramel flavours and any fruitiness tends to be reduced.
    – Megasaur
    Dec 25, 2012 at 23:17
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    This rather informative blog post indicates that the more volatile acidic compounds in coffee can be roasted out. Quinic and Citric acid, however, will remain even in a dark roast. Excessive amounts of Quinic acid come from incorrect roasting (poor heat transference) and citric acid from using immature beans. I'm not confident that re-roasting will really help, but it's not impossible.
    – Chris Steinbach
    Dec 27, 2012 at 21:18
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I don't think I would re-roast them. I think you would be better off trying a different grind, or preparing the coffee with a different method. Find ways to work with the acidity, basically.

A coarse grind and a french-press might work a bit better with the brightly acidic beans.

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  • For moka pot and french press I always grind it coarsely. Though in this case particularly it does not change much, so this is why I came up with the idea of re-roasting.
    – Raf Szalansky
    Dec 26, 2012 at 17:49
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Sour could be under-roasted, but it could also just be that particular bean variety, or the age of the bean. I would not try re-roasting already-roasted coffee.

What I would do is blend those beans with something to complement them. You can find flavor charts around the internet, such as this one from Coffee Bean Corral.

I'd probably look for something in the "Earthy" and "Chocolatey" realm. Maybe a Brazilian or Colombian. And if you like the roast flavors, look for something that's been roasted to a city+ or so. In addition to the color, oil on the beans is an indicator of a darkly-roasted bean.

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Another vote against reroasting. The general consensus I've seen over the years from hobbyist roasting forums is that once the roast loses temperature, that's it, there is no saving from reroasting.

Although I don't believe bitter is the opposite to sourness, extracting on the bitter side will help and possibly make it drinkable. To pour bitter you can try a combination of techniques such as:

  1. Extracting at a higher temperature
  2. Grinding finer and overextracting
  3. Pour longer, getting more of the bitterness that comes at the end of the pour after blonding.
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Why not try a small batch and decide for yourself. Rather than throw out beans, I’ve reroasted beans which were too blond for my taste, they were too expensive to just pitch. They tasted pleasant and milder after a reroast. I know all the experts naysay reroasting but it’s you that’s going to drink it.

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I agree with the above sentiment that re-roasting is probably not a good idea, and offer an alternative suggestion for salvaging the beans.

If you are not opposed to flavored coffee, a bit of cinnamon and/or clove thrown in with the beans when you grind them could hide the bitterness.

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