Rate of Rise

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Postby FuelSoGood » Mon Oct 13, 2014 11:19 am

Hello All:

I'm roasting on a San Franciscan and currently track roast profiles on log manually. The ROR initially increases after charging and then as the coffee roasts, I note a deceleration until about a minute or two prior to first crack. During this 1-2 minute span of time, there is a flatline/stall effect in the ROR. From research, it is my understanding that the ROR should constantly decelerate even at this 1-2 minute mark prior to first crack. Any suggestions as to how to fine tune this element of our roast process? Thanks much! :D

Best,
Brenda
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Postby N3Roaster » Sat Oct 18, 2014 9:21 pm

Whether it should or not is dependent on the coffee and what you want to do with it, but if you want to do this you might find it easier to work backwards. Start with where you want to end and where you want the ROR to be at that point and work back from there to see what your measurements should be throughout the roast. Write it out. Once you know what your plan ought to be it's just a matter of replicating that in practice. Be sure to taste each to verify that the change is one you like.
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Postby FuelSoGood » Wed Oct 22, 2014 10:43 am

Thanks, Neal.

So, can you help me understand what is protocol/standard? Is the ROR constant deceleration a recommendation or just adopted as a technique based upon the roaster's decision making?

I am just trying to figure out if this is a standard or not. I appreciate your feedback.

Best,
Brenda
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Postby N3Roaster » Sun Oct 26, 2014 9:13 am

There are effectively no industry-wide standards for what a profile should look like in production roasting aside from that there are some characteristics that correlate with roast defects. There are some who recommend what you describe as part of a wider set of constraints on roast level and overall batch time as something that produces results that they like. There are others who have looked at their own data and report no evidence that this advice is generally applicable. Personally I've gotten some very nice results with such a profile, but I've also had the rare coffee where it is simply impossible to produce an acceptable cup doing that.

Broadly, the way I look at it is that you're dealing with a lot of chemistry. So with all of these reactions that happen during the roast you need to have a certain amount of energy for the reaction to start. That's what you're measuring with the bean temperature. You also need to have the materials that are breaking down or combining, and what you start with will differ from one lot of coffee to the next as evidenced by our ability to roast one lot of coffee consistetly and getting different results in the cup when applying the same profile to a different coffee. So there are ranges where all of these reactions are happening and as a roaster you can allow those to progress for more or less time. That corresponds to a lower or higher RoR, but in this context that's just a notational convenience. So if you're tasting something in the cup that's a result of something that breaks down during the roast, you can get more of that by not roasting to a high enough temperature to start that break down or by progressing through that range at a faster rate and if you're tasting something in the cup that's a result of something that's synthesized during the roasting process you can get more of that by taking more time in the range of temperatures where that's produced. But as roasters we don't really have the facilities or background to deal with the chemistry directly and the reaction network is really complicated (most of the chemicals we'd be interested in fall into both of the above categories) and most of the time we're not looking at just one chemical, but looking for a balance among hundreds of them so we need to generalize a bit. Try something, taste it, consider what if anything should be changed, decide what change is likely to produce the desired result, try it, taste it, decide if that change had the desired effect, repeat as needed.

Personally, I find RoR much more useful with that automatically generated and plotted by a computer as an aid to roasting consistently regardless of profile. It's a much less useful concept without technology.

I made a video a couple years ago describing the process I use for product development that you might find interesting. http://youtu.be/sct2FWVkmDw
Neal
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Posts: 66
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Postby FuelSoGood » Thu Nov 13, 2014 11:44 am

Thanks so much of your detailed response! I truly appreciate it and will check out the vid.

Best,
Brenda
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Joined: Thu Jul 24, 2014 12:26 pm
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Roasting Since (Year): 2014

Postby Jeremias » Tue Jul 19, 2016 5:34 pm

Hi Brenda,
They're many opinions on what you RoR should be doing and where. I've explored a few of these approaches and, so far, am quite happy with the Scott Rao approach of having a constantly declining RoR. I don't remember if it was Rao or if I read it elsewhere, that stated that the RoR shouldn't flatline, much like that stall right before you go into 1C. I've been sticking to and been happy with trying to constantly decreasing heat to what essentially seems like falling through that stall into 1C. The key really is having sufficient heat at the beginning of the roast and having the right momentum going into 1C. I feel like by keeping to this principle of constantly decreasing heat and having a declining RoR I get the very clean and sweet tasting profile I'm after.
Hope that helps or gives you some insight.
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