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I just read online that some people roast their coffee bean before they grind the bean, to adjust the flavor. This sounds really interesting, and I would like to try. I would like to do this properly, and I am wondering about couple of things:

  1. What temperature to use, and for how long? I would imagine that this is determined by the current roast of the coffee and the target roast I would like, is there any kind of lookup table as a guidance?
  2. Some people mentioned cooling and de-gas after roast. What does that mean? I understand the cooling part, but what kind of process is de-gas - I guess it is some process happening on its own as the bean is cooled, but I am curious what exactly it is.
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    Are you asking about roasting beans a second time to after they have been purchased roasted, or roasting green beans? I haven't ever heard anyone discuss re-roasting coffee (roasting it a second time). It seems like far more work than simply buying beans that were roasted properly the first time.
    – Suspended User
    Dec 7, 2015 at 4:31

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Your first question isn't clear exactly. All drinkable coffee has been roasted first, as raw coffee beans are not edible. I've read that re-roasting beans isn't practical for some reason that I'm not clear on, but I agree with Peter Pei Guo's, comment about why you would want to re-roast coffee in the first place.

Immediately after roasting, coffee beans produce carbon dioxide gas as a result of the chemical changes happening inside the bean. This gas takes some time to be released from the interior of the bean, anywhere from 3-5 days.

I've brewed my own home roasted coffee immediately after roasting to see if this is really true, and yes, it is.

Immediately after roasting the coffee has a really harsh, sour taste from the acidity that accompanies carbon dioxide gas (carbolic acid). It also foamed (bloomed) really violently with the addition of hot water. After resting the roasted coffee for about 5 days, the coffee from the same batch of beans tasted great.

One of the indicators of freshly roasted coffee beans is the bloom that they produce as some residual carbon dioxide gas is released with the addition of hot water.

As time passes and the beans begin to stale a bit, the bloom lessens, then disappears. After properly resting freshly roasted coffee however, the small amount of residual carbon dioxide doesn't affect the taste. Immediately after roasting however, the carbon dioxide levels are too high to allow good tasting coffee when brewed.

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    I find that for most of my beans 24 hours is enough rest. I get optimal flavor from 3 to 5 days after the roast. If I rested as long as you are describing, I'd miss that window.
    – Suspended User
    Dec 8, 2015 at 18:51
  • I suspect it depends on the particular bean and roast level. I found 24 hrs to be too short for the east African beans i normally use.
    – PJNoes
    Dec 8, 2015 at 22:43

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