One thing that does not appear to be included in this roaster and which you might find useful to add, Jon, is an inline gauge for the measurement of fuel (propane in this case) consumption. This is something I retrofitted on my own roaster which I have found very useful; it was a professional roaster who advised me to consider adding this a number of years ago, and not my own idea. This is more or less the same idea as the amp meter on the M3 Quest roaster, but is more useful because with a gas heat source the response is almost immediate, where as with electricity the response is so slow as to be of very little use for on-the-fly adjusting.

In retrofitting this you will probably need to install it inline before the gas enters the adjusting valve and then the roaster's burner(s). The result of this is that you will probably be measuring "backpressure," and hence will get an inverse reading. This means that as you increase the flame height of the roaster's burner, the reading on the gauge will GO DOWN, rather than up. It really doesn't matter, as long as you understand what is going on, because what you are looking for is a repeatable measure of gas flow to the burner that will aid you in roasting. The way I use this information is that there are several points in a roast cycle where I can associate a certain gas input with a certain approximate result, as it relates to temperature change over time in the roasting process. Once set, I can then adjust the flame height depending upon what it does to the bean temp over time. It gives me something to start with and something to adjust from as a roast evolves.

There are other roasters in the 1lb to 1kg range that include this sort of gas consumption gauge as a standard item when the roaster is purchased, so clearly I am not the only one who thinks this provides useful ancillary information.

ken

Thanks Ken,
It appears to me like this gauge may already be present at the inlet regulator, but I will need to learn how the readings relate to roast parameters.
-Jon

Rather than a gauge, get a variable area meter or rotameter for gas flow metering. You can read the gas flow directly and instantly by reading the height of the ball in the tapered tube. I use them in the lab all the time for metering shielding gas and other reactions and they work well and dont tend to break. They usually have a very precise needle valve as part of the assembly. With one of these you know exactly how many BTU's you are pumping in and can correlate that to differing bean masses for easy computation to do the same roast for whatever batch size you desire.

kmills wrote:With one of these you know exactly how many BTU's you are pumping in and can correlate that to differing bean masses for easy computation to do the same roast for whatever batch size you desire.

I love the idea of having a flowmeter to measure actual gas usage, but I'm skeptical that there's any "easy computation" to directly correlate whole roast profiles for different bean loads because of the complexity of the heat transfer process and my ignorance about how changing the bean mass affects the heat transfer mode(s) and rate(s).

Although I do agree that such a precise direct measurement may be very helpful in many ways, so I plan to go check the Omega catalogue for something appropriate that will be inexpensive and easy to install.

Is the large black cylinder in the rear an afterburner or a chaff cyclone? If it is an afterburner... is it available without one?

Phaelon56 wrote:Is the large black cylinder in the rear an afterburner or a chaff cyclone?

It's just a chaff collector, no burner. It seems to be very effective and every 6-8 roasts I clear out a big pile of fluffy, not-charred chaff

Thanks for sharing the details on your new roaster Jon- it looks like something I'd have seen in the corner of my cold-war-era equipped college 'materials engineering' lab-- I mean that in a good way.

Out of curiosity, how responsive to inputs is it, and what's the fastest (consistent) rate-of-rise for your typical batch size you've recorded?

rama wrote:Out of curiosity, how responsive to inputs is it, and what's the fastest (consistent) rate-of-rise for your typical batch size you've recorded?

I have been charging with a full pound of beans. They say I can roast more to finish with a full pound or less (down to 3-4 ounces), but for now I'm keeping this constant until I understand the process better.

The fastest rate was WAY too fast, recorded after preheating the drum to 400°F. Beans went from ambient (70-ish) to second crack (400-ish) in about 4 minutes.

Now I preheat the drum somewhere between 320°F and 340°F and bean temp typically reads a rise of around 20-25 °F/minute during drying (after the turn) and then I am running 15-25 °F/minute from dry to first crack and now I'm working at running 10-15 °F/minute from first crack to end of roast

It's easy to go slower or faster, but I'm tying to stay around these ranges for now.

Does the PID send a control signal to a solenoid to control the flame and is it just an on off signal? This seems like a pretty reasonable home build, my mental gears are spinning....

kmills wrote:Does the PID send a control signal to a solenoid to control the flame and is it just an on off signal? This seems like a pretty reasonable home build, my mental gears are spinning....

Yes. Here's a quote from the initial post:

JonR10 wrote:The temperature controller is a Watlow PID but it is set to signal only ON/OFF, and mainly used as a temperature readout off of the probe in the bean mass (directly under the sightglass). Temperature ramping is controlled manually by means of a precise needle valve on the gas feed to the burner.