Measuring your MET on Nano 7 and the impact of batch size
Posted: Mon 21 Oct, 2019 5:08 pm
Update 27 Oct 2019 : Apologies all. It looks like the original thermocouple sensor that I used was on its way out, hence leading to incorrect temperature reading and observation....
Hi all,
Sorry for the lack of update...life's got in the way.
Just want to share a finding and possibly get some input/confirmation from y'all to check that it's not all just in my head...
After many years of roasting on the Quest M3, one thing I've learned is that monitoring the MET (Maximal Environmental Temperature) can be quite crucial. Obviously the Nano 7 is quite a different system, but the concept still applies : A high MET may mean that some of the beans are experiencing high temperature locally and may pick up some unwanted roast defects. I had some questions about the probe placement of the Nano 7, so I got curious and wanted to know how the MET tracks on the Nano 7 (compared to the usual BT probe) .
About the impact of MET on roast quality, Jim Schulman did a much better job in explaining that than me:
https://www.home-barista.com/home-roast ... ml#p538330
So in one of the weekends, I snaked a bare k-thermocouple into the vent of the Nano 7 and did a couple of roasts as per usual (Steve you may recognize the meter ).
So by doing this, I get the 'MET' reading through the k-thermocouple, as well as the 'BT' as read by the usual BT probe on Nano 7. I extract the roast logs and overlay them in Artisan.
These are my results below (I've got more roasts but these two are representative enough). So, again, the same coffee, same profile (stock Firestarter), but roasted at different batch size.
Mainly, note that the spread between the 'MET' and 'BT' between 50g load and 100g load.
In restrospect, it is not unexpected that you needed hotter air(and more energy) to roast more coffee. What was surprising to me was that in some of the roasts, the MET got up as high as 270 deg C for the higher 100g load. 270deg C may have been in what some considered to be the 'scorching' territory. As an additional observation, I had some experimental roasts cupped blind in one of our cupping sessions back in Aug (basically a couple of us coffee nerds in Melbourne getting together). For the cupping, I have a coffee roasted with the same profile and same drop point, but one was loaded at 50g and the other at 100g. The 50g-roast came out tasting more superior than the 100g-batch roast on the cupping table. So this MET observation seems to support it somewhat. In later roasts with larger batch size, I tried to compensate by roasting to a lower roast level number, but that did not seem to work (tasted too light and coffee didn't taste as good, but that's once off experiment).
If you're nerdy enough and happen to have a logging thermocouple sitting around, I would be curious to see what your MET looks like.
I shared this with Chris and he also gave me another useful tips. He mentioned that not all vents put out heated air at the same temperature, so you might want to verify the vent which you're measuring is the hottest spot. To do that, you need to start the roaster empty (no beans) and go into the 'secret' timer mode (it's in the instruction booklet). I haven't got around to repeat this with Chris' suggestion, but that's in the plan.
Alternatively, if you just place the probe at the vent which looked most discoloured, my gut feeling is that there's where the hottest air is coming through (I may be wrong though).
So if you're chasing clean light roasts (and are using Firestarter profile), especially for filter, may be give this a shot by halving the batch size (50-60g) and see what you think. I found that stock Firestarter profile, 50g load, roast level 2.2 seems to give me the best results so far (compared to my own profiles).
If what we observed is valid, another implication is that when we're designing a roast profile, the ramp after first crack shouldn't be too steep for larger batch size, otherwise you may get into this too-high MET scenario. This also can be evidence for why it's ok to have almost flat/zero ROR during development phase (the MET may still be going up, but not picked up by the BT probe)
p/s: changed the title to better reflect the batch size is apparently what is affecting the MET
Hi all,
Sorry for the lack of update...life's got in the way.
Just want to share a finding and possibly get some input/confirmation from y'all to check that it's not all just in my head...
After many years of roasting on the Quest M3, one thing I've learned is that monitoring the MET (Maximal Environmental Temperature) can be quite crucial. Obviously the Nano 7 is quite a different system, but the concept still applies : A high MET may mean that some of the beans are experiencing high temperature locally and may pick up some unwanted roast defects. I had some questions about the probe placement of the Nano 7, so I got curious and wanted to know how the MET tracks on the Nano 7 (compared to the usual BT probe) .
About the impact of MET on roast quality, Jim Schulman did a much better job in explaining that than me:
https://www.home-barista.com/home-roast ... ml#p538330
So in one of the weekends, I snaked a bare k-thermocouple into the vent of the Nano 7 and did a couple of roasts as per usual (Steve you may recognize the meter ).
So by doing this, I get the 'MET' reading through the k-thermocouple, as well as the 'BT' as read by the usual BT probe on Nano 7. I extract the roast logs and overlay them in Artisan.
These are my results below (I've got more roasts but these two are representative enough). So, again, the same coffee, same profile (stock Firestarter), but roasted at different batch size.
Mainly, note that the spread between the 'MET' and 'BT' between 50g load and 100g load.
In restrospect, it is not unexpected that you needed hotter air(and more energy) to roast more coffee. What was surprising to me was that in some of the roasts, the MET got up as high as 270 deg C for the higher 100g load. 270deg C may have been in what some considered to be the 'scorching' territory. As an additional observation, I had some experimental roasts cupped blind in one of our cupping sessions back in Aug (basically a couple of us coffee nerds in Melbourne getting together). For the cupping, I have a coffee roasted with the same profile and same drop point, but one was loaded at 50g and the other at 100g. The 50g-roast came out tasting more superior than the 100g-batch roast on the cupping table. So this MET observation seems to support it somewhat. In later roasts with larger batch size, I tried to compensate by roasting to a lower roast level number, but that did not seem to work (tasted too light and coffee didn't taste as good, but that's once off experiment).
If you're nerdy enough and happen to have a logging thermocouple sitting around, I would be curious to see what your MET looks like.
I shared this with Chris and he also gave me another useful tips. He mentioned that not all vents put out heated air at the same temperature, so you might want to verify the vent which you're measuring is the hottest spot. To do that, you need to start the roaster empty (no beans) and go into the 'secret' timer mode (it's in the instruction booklet). I haven't got around to repeat this with Chris' suggestion, but that's in the plan.
Alternatively, if you just place the probe at the vent which looked most discoloured, my gut feeling is that there's where the hottest air is coming through (I may be wrong though).
So if you're chasing clean light roasts (and are using Firestarter profile), especially for filter, may be give this a shot by halving the batch size (50-60g) and see what you think. I found that stock Firestarter profile, 50g load, roast level 2.2 seems to give me the best results so far (compared to my own profiles).
If what we observed is valid, another implication is that when we're designing a roast profile, the ramp after first crack shouldn't be too steep for larger batch size, otherwise you may get into this too-high MET scenario. This also can be evidence for why it's ok to have almost flat/zero ROR during development phase (the MET may still be going up, but not picked up by the BT probe)
p/s: changed the title to better reflect the batch size is apparently what is affecting the MET