So I finally got a chance to try a roast with the thermometer. At approximately 3.5 minutes into the roast in the reading it crossed 482 and would no longer read. This is OBVIOUSLY not a correct reading. I expected some imperfection in the readings due to this probe expecting liquid/solid meat as opposed to air/dry readings but everything is significantly off. First crack came as a reading of 449 which puts me a good 50 degrees above where I expect to be and follows about 50 degrees over everything I expected during the roast for the color changes etc.
My theory is that the probe is so long that it has to be inserted through the grate on the chaff collector on top. The probe is then picking up heat transferred by the chaff collector that it is touching and particularly the metallic disc embedded in the lid being transferred through the plastic.
The cooling cycle lasts approximately 2.5(ish) minutes and it ends at an unusually high number. With the probe and chaff covered removed and sitting 5+ minutes it still shows a temperature in the 90s so this is certainly picking up the temperature from the cover. At this point I will need to attempt to remove the probe in some way and see what else I can do to “shrink” the size of the probe and find an alternate place to put it.
[easychart height=”300″ type=”line” title=”Heat Results” groupnames=”Temperature F” valuenames=”0.0,0.5,1.0,1.5,2.0,2.5,3.0,3.5,4.0,4.5,5.0,5.5,6.0″ group1values=”78,222,366,402,413,428,460,482,482,482,482,482″ group1markers=”6.1″ hidechartdata=”true” ]
[easychart height=”300″ type=”line” title=”Cool Results” groupnames=”Temperature F” valuenames=”0.0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1.0,1.1,1.2,1.3,1.4,1.5,1.6,1.7,1.8,1.9,2.0,2.1,2.2,2.3,2.4,2.5″ group1values=”482,482,474,402,320,262,240,212,201,183,172,167,158,152,147,141,140,138,138,132,129,127,127,127″ hidechartdata=”true” ]
While the HEATING is flawed with the metal disc and the cooling is most certainly flawed at the end as well it is interesting to witness the significant drop in heat from the cooling cycle. The beans (by touch) clearly release heat faster than the metal mass does and they are quite cool in the end. In about 30 seconds the heat has dropped to around 250 with the metal heat skewing the readings. It is my guess that all cooling readings are approximately 30-40 degrees higher than actual in the bean mass meaning the real “roasting” has stopped before 30 seconds of cooling are up.
Lesson Learned: The chaff collector gets significantly hot enough that you need to avoid ANY contact to any probe devices with the top and try to steer clear of the metal disc at all costs.
Update: I have used a copper pipe cutter to slowly slice a ring around the metal casing of the thermometer allowing me to shorten the probe. I googled around and found this article http://brettbeauregard.com/blog/2009/09/anatomy-of-a-digital-thermometer-probe/ which shows the inner guts of a typical probe. As you will see this is mostly the braided wire until the very end where the actual sensor is. I’ve sliced off several inches of the casing and slid it up the wire towards the socket. Once I determine if this seems to work I will try to figure out a way to slide this off without mucking things up too much and permanently removing it and crimping the end of the probe onto the braid. New article once I get to that stage if it works out.