Hi guys,

I have a question that is, in all likelihood, very simple to answer (potentially indicating that I'm simple ).

I have an MET probe from EricS which I place in the top right bolt holding the bean loading chute/chimney to the front of the roaster. When I open the bean chute or the cooling tray the MET shoots up a lot (say 25-35*C). What is the difference between an open bean chute and a closed loop with the fan on? Why does the temperature change so dramatically? What is the true MET (open or closed loop)?

Thanks,
Terence

I'd say it's because heat rises and you've created the potential for a stronger draft with the lid open. Not a lot of air flows thru the drum, but most of it flows around it. With the lid open, it allows for that super heated air down near the elements to rise up where your probe is.

Thanks... so the real MET is closer to the number when the chute is open I presume.

It's rather dynamic, but you can trust the measurement you're getting either way, door open or closed. It's also only relative to what's happening with the roast. Pay less attention to the specific numbers individually, and just correlate your temps to your stages of the roast. As long as you can get consistency down (with temp trends), the numbers aren't concrete things to focus on, rather, abstractions of the roasting process.

Please use your heads.

If the hatch or flap is up, there is no airflow. When there is no airflow, there is sharply reduced heat transport, and a sharp drop in the correlation of the measuring point to other parts of the system. The sensor is just above the heater, and will jump quickly. This no longer reflects the environment of the beans, but it does reflect the environment of the heater. Since the heater can burn out; running a lot of heat without running the air is foolish and very ill advised.

Quite frankly, the more idiots buy this roaster, the worse it will get; since the manufacturers will be compelled to add more and more performance degrading idiot proofing. So when using the Quest, and basically whenever home roasting period, please try to curb your inner idiot, and use some common sense.

I should clarify. Terence, I'm not calling you an idiot; I'm saying we all tend to do idiotic things, and we need to resist that urge when home roasting.

The nice thing about the Quest is that it is not idiot proofed: you can destroy it, start fires, incinerate the chaff or beans, etc etc. The reason this is nice is that it allows you to fully control the roast. But it does mean you cannot go "let's see what happens if I try this" without thinking it through ahead of time.

The Quest is a home roaster that's so controllable that people five years ago said would never be put on the market due to liability issues. If people do end up having accidents, nobody will be willing to sell it. I'd hate to for that too happen, so I overreact a bit when people aren't careful with it.

I'm using my head quite well, thank you.

Jim your statement is abrasive on many points and your use of words like "idiots" only serves to degrade the dialogue and I find it personally insulting. First, your point of there being no airflow is not 100% accurate. There is airflow albeit small. If the fan is running, it is drawing air thru the horizontal exhaust tube, plain and simple and it's something we all can agree on. Air can and will be entrained from the chute area, even with the lid open although it has little bearing on the roast itself specifically since it is so miniscule. And I'm not even arguing what it's affect is when beans are in the roaster, that's another entirely separate point. But plain and simple, if you have the roaster idling or pre-heating empty with the fan on, and you lift the bean loading door, some heated air will still flow up out of the chute, from the draw from the fan acting like a flue and from the simple fact that heat rises. I wasn't going into a prolonged lecture about the physics of what's happening, but to avoid being labeled an idiot, I suppose I have to.

Terrence, to answer your question more directly, the reason there's a spike in the MET when the flap is up or the chaff door is open is simple. The fan moves the heat thru the system, and when the loading door is open, most of the flow of air in the system ceases (and for the sake of argument, during an actual roast, it's not enough to affect the beans, so it's effectively absent). That airflow that was pulling the heat away from the elements is now gone, and the stored radiant heat rises as a result, because heat energy is being put into the space at the same rate, but it's no longer being eliminated at the same rate, the heat goes up plain and simple. This is what I meant by it being a very dynamic phenomena. It's one very specific set point of data at one very specific time, and it wont help you steer your roast, because it's capable of changing very quickly just by opening and closing the door. You'll be chasing a dragons tail if you're trying to control it too tightly. Just know what your trajectory is and it will be easier to know what changes you need to make.

If you step back and see the big picture of where your MET is, and where it's heading, you'll better understand how to mold it to get what you want. Seeing a 80°F bump in temps for a few brief seconds isn't something to try to chase down and control. What I'm trying to say more simply, is if you're pre-heating the roaster, you don't need to fear cutting the heat dramatically just because you see a bump in the MET. You do, however, need to practice a bit of common sense and not run the elements full out, without any fan for a prolonged period of time, without the risk of destroying your elements or even worse. If I see a large bump in the MET between roasts, I'm not that afraid, because I know it will quickly correct itself once there's either a batch of cold beans soaking up the beans added into the drum, or I turn the fan on. Either way, I'm making a change in a short period of time. I'm not letting my MET skyrocket without keeping it in check.

There's a time and place for a lecture on Quest usage that doesn't entail burning your kitchen down. This wasn't it. It was simply a question about the MET phenomena at certain stages of use.

Thanks Tom and Jim,

There is context to this thread, and no I haven't done anything close to dangerous with my Quest.

Specifically I've been running lower and lower MET roasts with correspondingly slower temperature ROR profiles in a bid to properly roast small and low grown beans like Maui Mokka. I've even had some issues with high grown small beans such as Mocha Ismaeli (ridiculous I know). I've been stretching out the Ismaeli roasts to about 18 minutes in total with an MET getting down to close to 230*C and yet have still had some smokey and ashy results which I've found hard to credit given that (a) the bean should tolerate heat well and (b) highest MET is really quite low in the scheme of things (at least to my understanding).

I've been able to achieve extremely good roast results for the majority of beans that I've bought over the 150-200 roasts that I've completed. It's really an edge case discussion so that I can successfully roast specific types of beans.

Jim, thanks for clarifying that you're not specifically calling me an idiot. I'm a big boy and I'm trying to soak up as much as I can from this site so that I can maximise the operating spectrum of my roaster.

Tom, thanks again for chiming in. Your help with Quest modifications has been invaluable.

Terence

Oh... and to be clear I'm not running the roaster with chute open (even in drying phase) nor without air flow. I think I've noted before that my version of the Quest demonstrates some of the idiot-proofing that Jim refers to (there is always some level of air flow even at the lowest fan setting).

TomC wrote:Jim your statement is abrasive ... I wasn't going into a prolonged lecture about the physics

First off, I will continue to be extremely abrasive when it comes to safety issues in home roasting. It's not just preventing accidents, that's an issue in all hobbies. But homeroasting also exists in a bubble as far as liability is concerned: many smaller roasters are not UL (especially after being modified); and fixed large roasters are not mentioned in building codes. If insurances refuse to cover roasting mishaps; it will put a big damper on the hobby.

Second, the original question was about the relative accuracy of readings with the fan in line and not.

• Obviously readings close to the heat will be higher if the fan is low or off.
• More importantly, the less airflow, the more uncorrelated the temperatures in various sections of the roaster become. This means the temperatures recorded by your probes are a better sample of the overall temperatures when the airflow is fat enough to remove hot and cold spots.
• Most important, the more even the temperatures the bean mass experiences, the better the roast. Drum roasters tend to be better than air roasters because there is usually about a 100F difference between the entering and ixiting air, whereas in drum roasters the drop from highest to lowest is usually half that. I don't know the exact response of the temperature variance to airflow, but it's clear that with no or very low airflow, and a lot of power to the heaters, there will be hot and cold spots.

Skilled bakers go to great lengths to make sure the temperatures in their ovens are even and steady; the same applies to roasters.