Newbie roaster trying to understand my goals in roasting - Page 3

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
walr00s (original poster)
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#21: Post by walr00s (original poster) »

Beeroclock wrote:Hi walr00s, you're getting some great advice here bicktrav your opening post was a gem! The issue with the Sandbox is it doesn't have a probe anywhere near the bean mass. As you've mentioned it's an ET probe only so in order to progress you're going to have to roast by ET data only, whilst this is possible it does make the process harder, as you're never going to really know what the end temp of the bean is, just the environment it's been subjected to.
Interesting, I thought ET was the ambient air temperature within the roaster or within the drum rather than the temperature of the air moving away from the surface of the beans? If I run my roaster with the drum in but no beans, the reading immediately goes to ~10-20C lower than whatever my charge temp was. Does this mean that the ET drops ~100C more when I put beans in the drum (since that's what the probe reads)?

Beeroclock

#22: Post by Beeroclock »

ET or environmental temperature can be measured in a variety of places either in the drum or in the exit path of the airflow. Gives one a good indication if where a roast is going, airflow will have a very direct influence on its reading. Often when a bean probe is placed incorrectly and picking up more air than bean mass readings become more jumpy.

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Peppersass
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#23: Post by Peppersass »

This highlights that BT probe measurements in all roasters are an approximation of what's going on with the beans -- at best.

It's obvious that a even a probe buried deep in the bean mass can't measure the internal temperature of the beans. At the very best, it measures the surface temperature of the beans, which doesn't tell you how much heat has penetrated the interior of the beans. And my guess is that in a lot of roasters, or maybe most roasters, the BT probe isn't telling you the surface temperature of the beans, but some combination of that temperature and the air temperature between the beans (i.e., the close-in air temperature.)

We guess that when 1C starts, and a certain amount of time has passed, and the surface temperature gets to a certain point, the beans will be developed to the point we desire. Of course, with a bean we haven't roasted before, we often find that our guess is wrong and we have to adjust DT and/or drop temperature. Once we get a roast we like, then the BT measurements are very useful for reproducing it. I think that's their primary value.

My Ikawa, and probably other fluid bed roasters, measures incoming and exhaust air temperature. The profile is based on exhaust temperature, which is the air coming off the beans on its way to the chaff collector and exhaust chimney. The incoming air temperature is adjusted so that the exhaust temperature follows the pre-programmed profile. This seems to work just as well as (perhaps better than) BT measurements taken deep in the bean mass of my Quest drum roaster. The exhaust temperature is a function of the temperature of the air around the beans (likely somewhat lower because the probe is short distance from the spinning/lofting bean mass), which in turn is a function of how hot the incoming air is, how much it's cooled off getting to the beans, and how much heat is being absorbed or emitted by the beans (assuming you believe in the exothermic reaction theory.)

Roa would no doubt argue that RoR measurements derived from BT readings help us to ensure that the temperature on and around the beans is rising at a declining rate, not crashing or flicking in 1C, which many have found affects taste. I see no reason why exhaust temperature RoR wouldn't give us the same information. [That said, RoR curves on my Ikawa don't look much like the RoR curves on my Quest or other roasters, which could be an artifact of the scale and smoothing used. Or, it may indicate a fundamental difference between BT and exhaust probe measurements. I plan to have a discussion with Ikawa about that.]

Despite questions about the RoR curve, based on my results with the roaster, exhaust temperature measurements work just as well for timing and manipulating the roast phases as a BT probe buried in the bean mass, and definitely work just as well or better for reproducing a previously successful profile.

Beeroclock

#24: Post by Beeroclock »

Not arguing that BT temps are absolute, but at least with a well placed BT probe one can get a good idea of dropping/end temp for the bean. This and colour of the bean plus time after FC are how I judge my roasts.

The issue I have with the probe in the Sandbox is that it always gives an end temp lower than the FC temp which obviously isn't the final temp of the bean.

walr00s (original poster)
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#25: Post by walr00s (original poster) »

Beeroclock wrote: The issue I have with the probe in the Sandbox is that it always gives an end temp lower than the FC temp which obviously isn't the final temp of the bean.
It does? Maybe that means I'm doing something wrong?

Beeroclock

#26: Post by Beeroclock replying to walr00s »

Nope not necessarily, if you look at all of the roasts from the article that you linked by Dave C then you'll see the exact same issue. I did point this out some time ago on another forum.

Therefore you will need to start logging your FC temp and then drop based on time after FC only and you will likely not know if a bean has crashed or flicked thereafter. Whether that bothers you or not is another story.

Looking at the graphs you've posted where you have logged FC and then drop time - it would seem that you are only allowing 10-15 secs development time. I would start by stretching this out to at least 1min 15secs or more.

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Peppersass
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#27: Post by Peppersass »

Beeroclock wrote:The issue I have with the probe in the Sandbox is that it always gives an end temp lower than the FC temp which obviously isn't the final temp of the bean.
This is true of all the profiles in the article, but not all of the OP's profiles. Some have the end temp and 1C temp the same, other have the end temp a degree higher.

That's not good, but I don't think a drop in temp or flatlining between 1C and end is inherent to the roaster. I don't see how the probe or placement could cause that. It looks like a flaw in the profile -- i.e., insufficient heat after 1C to carry the roast to the end. That's clear from the RoR curves.

My guess is that heat is being reduced too much before 1C or airflow isn't strong enough. Now, if the profile is using whatever combination of heat and airflow maximizes heat at 1C, keeps it at that level, and the end temp is still less than 1C temp, then yeah, something is screwy with the roaster design.

You would think the built-in profiles wouldn't cause the problem, but it could be that they were designed with beans of significantly different density and/or water content from the beans used by Dave C and the OP.

walr00s (original poster)
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#28: Post by walr00s (original poster) »

Beeroclock wrote: Looking at the graphs you've posted where you have logged FC and then drop time - it would seem that you are only allowing 10-15 secs development time. I would start by stretching this out to at least 1min 15secs or more.
Thanks for the help! Now that you say that, I think I did see your post before purchasing but didn't fully grasp the significance. I guess if the temperature measurement is consistent, I can still use it to mark Drop Temp even though it's obviously not the actual bean temp?

I've been really bad about marking FC because the FC behavior has been so different across roasts. Sometimes I get a nice vigorous FC all within a 15-30s span, and other times I'll get outlier pops as much as 2.5 min apart and virtually no continuous popping periods. What I've been doing instead is just manually lowering the heat setting and increasing fan when the first pop happens and then if it seems like the temp is crashing and/or the rest of the beans aren't popping, gradually ramp heat up and fan down until it stabilizes. I'll switch back to using the 1C button, I guess at first pop? Seems like it's hard to be consistent when 1C itself is so inconsistent.

walr00s (original poster)
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#29: Post by walr00s (original poster) »

Peppersass wrote: You would think the built-in profiles wouldn't cause the problem, but it could be that they were designed with beans of significantly different density and/or water content from the beans used by Dave C and the OP.
I think it's actually worst with the official profiles, at least based on my roast history info. Here's a couple of examples:




The 100g Medium Roast tasted...I guess baked? It tasted really flat and uninteresting and joyless. This was with lower quality beans (Primos, supposedly a direct from farm in Nicaragua purchased through Amazon, mainly as something to cheaply experiment with). But both the 100g Light Roast and my own profiles tasted far better than that 100g Medium official profile with the same bean.

Beeroclock

#30: Post by Beeroclock »

If you place an ET probe in the exhaust of a traditional drum roaster (rather than in the drum near the top away from bean strike) - you will often see it dip below the BT probe towards the end of the roast as airflow is high and heat is low and in essence the bean temp is rising due to residual heat in the drum and machine itself as well as the beans.

I think the location of the probe in the Sandbox is acting the same way and measuring the cooler air your getting at the end of the roast. This is why you can't rely on the probe readings after FC, you're going to have to properly mark your first crack and then do some guess work/experimentation on development after that. My guess is that you're using too much airflow at the end of the roast. Might be worth getting a handheld laser thermometer so that you can get an idea of the bean temp when you're dumping the beans.

Agree re Espresso Vision Roast Vision - it's a very handy tool and I use mine all the time for consistency - also a steal at the moment with $50 off.

Cheers Phil