Time based roasting

[100Flash]

I do all of my roasting with a popcorn popper based on time alone.

2 questions:

How long is the average 1^st crack duration (not the time to the 1^st crack)?

What is the average time in-between the 1^st and 2^nd crack (Sweet Maria says 15 – 30 seconds…which leads me to suspect that I’m merging the cracks)

[cheddington]

You could potentially get several different answers to your questions, all of which are true only for the particular circumstances at the time of the measurement. The times you ask for will certainly depend on (1) the particular beans being roasted and the temperature of the roaster (which may be increasing during the time frames you ask about) and (2) the temperature of the roaster, which can vary even with a variable line voltage. For example, I doubt that my roaster is the same temperature as yours after 8 minutes of roasting, so it would be pointless for me to offer you a time for the duration of first crack. One could certainly provide values for several roasts, and you would have a range of values with an average and a measure of the variability. The more the factors vary during those roasts, the wider the standard deviation of the values I would get. And that would apply only to the conditions in which I performed the roasts, not your conditions. If you really want answers to your questions, you might as well generate your own set of data.

[scott stap]

I have found that the two cracks have different sounds to them. 

One is a pop pop pop almost like popcorn and the other is like a crackle that I always mentally relate to a forest fire. IF you have an unreasonably loud air popper (chinese knockoff variety) it tends to mask the difference.

I am assuming you are not using a thermometer. Stop by your big box lumber store and visit the grill section and buy the long grill thermometer ( http://goo.gl/qw5aJV ) poke a hole in the top of your plastic shroud and drop it down in there. You will have to use something to hold it up so it does not hit the bottom of the chamber but stops midway down. I usually use the clip that comes with the thermometer. Use that to watch temps.

I have found that if the safety switch is not bypassed that it will lead to confusing results. Sometimes you can roast sometimes you cannot and if you base it on time and not temp you may never know that it is not working.

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[Shane Lewis]

Hi there. Thanks for your email.  While I have never roasted on the popcorn popper, I do have extensive experience with drum roasting.  

The duration of first crack and the time between first and second crack is generally a function of heat.

The more heat that you put into the system the faster the entire reaction will occur.

The less you put into the system, The slower the entire reaction will occur.  

To take an example. If I have 1 pound of coffee in one of our 4 pound drum roasters, I would generally prefer to start at 470°F

Generally in this configuration, first crack will endure approximately one minute and we will have a one or two minute separation between first crack and second crack. 

However, if I push the heat to 575°, then the reaction happens so fast because it is receiving so much heat I can blend first crack and second crack together into one merged crack

If I roasted at 400°F instead, I can stretch out the length of the crack and stretch out the time between the cracks to as many as four or five minutes in between.

As far as I am concerned, with larger volume roasting, the time between cracks is ideally between one and three minutes depending on your temperature.  In my opinion, this should still hold true for popcorn popper roasting as well.

If you are blending your cracks together try reducing your heat by about 50° and see if you are able to detect separate cracks.  Depending on how dark the coffee is, you may not be getting two second crack yet.

I do consider Sweet Maria's an authority on coffee and on roasting so do not simply discard their answer. However, 20 sec seems like too short of a timeframe to me.  This may however be the correct methodology on popcorn popper roasting. 
Please let me know if I can help further.
Thanks,
Shane D. Lewis
404-787-7125

Thanks,

Shane D. Lewis

404-787-7125

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[100Flash]

Thanks for all the advice.  I assume that IF I can determine the 1st crack duration time and the time interval before the 2nd crack then:

If I use the SAME coffee beans and the SAME amount in the SAME popcorn popper at the SAME starting (whole body) temperature using the SAME voltage source then I should be able to use the above determined 1st crack duration in my time-based roasting without regard to temperature.