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Alternate BT Location:
The stock BT thermometer location is optimum for most batch sizes, but it
may be a bit too high for tiny batches. An alternate location is possible using one of the screw holes on
the drum door's sight glass. To do this, remove the uphill* M4 sight-glass screw, and drill a tiny hole in
the centre of it. Install a 1/16" x 6" thermocouple, such as the
Omega TJ36-CASS-116G-2.00-SB-
SMPW-M
through the hole
,
bent so that the probe protrudes only one inch inside the faceplate.
Although this probe will be subject to being impacted by the beans, its short length makes it strong
enough to function without being damaged by the beans.
*Uphill Definition: Use the left hole for clockwise rotation drums (before May 2013); use the
right hole for counter-clockwise rotation (MK-2) drums.
Tighten the screws securing the sight-glass carefully to leave the glass a bit loose.
ET measurement:
Quest roasters come equipped with an M8 tapped hole at the proper location to
measure the environmental temperature. This hole is closed off with a bolt. The same thermocouple
used for measuring BT will work here, although some users prefer a thinner probe, as it is more
responsive. When the roaster is empty, the BT and the ET measurements are nearly the same, being the
drum’s air temperature. Once charged, the ET thermocouple continues to measure the drum’s air
temperature, while the BT indicates an approximation of the bean temperature.
MET Measurement:
A modification to measure maximum environmental temperature (MET) is
possible. MET is a measurement of the temperature between the drum and the case. The easiest
solution is to remove one of the upper M4 hex screws securing the bean chute and insert a 1/8" x 6"
thermocouple between the drum and the shell.
For a better solution, drill a suitable hole in the centre of the M4 hex screw, and install a 1/16" x 6"
thermocouple, such as the
Omega TJ36-CASS-116G-6.00-SB-SMPW-M
. The beans cannot impact a
probe at this location. Therefore, one can install a long, thin probe; the lighter the probe, the more
responsive the readings will be.
This screw will be weaker than the other three holding the chute. Do
not torque it down beyond a little more than finger tight.
A 1/8" probe can protrude straight out and be pushed in or pulled out to achieve optimum readings; a
1/16" probe is too flexible. On an M3 roaster, to secure the thinner probe, bend the probe 90º 2.5” from
the cable end. Route the wire across the bean chute’s face to the side of the roaster, and secure it with a
cable tie. Be sure to bend the probe according to the manufacturer’s recommendations for a minimum
radius. On an M6 roaster, push the probe completely in, which will position it correctly.
The heaters on some roasters are mounted low in the roasting chamber; therefore, you can use either of
the two upper screw holes. The heaters on other roasters are different. As viewed from the front, the
left-hand one is mounted high; the other is mounted low. Therefore, to avoid having the probe close to
the upper element, we recommend mounting the probe in the right-hand hole.
The displayed value of the MET is highly dependent on the location of the probe. Even minor
variations in placement make significant differences in the indicated temperature. Thus, it is of little
use as an absolute value, especially for making comparisons between roasters. However, this is the
