Sonofresco (all roasters in general) heat source

[Tex]

I'm brainstorming here. I've been using a thermometer with a beaded type T thermocouple, placed midway in the bean mass for the last two roasts. What I'm seeing is making me wonder if the Sonofresco heat chamber is faulty.

Here's what I see;

• The beans start swirling as soon as you power up the roaster.
• Until the burner comes on the temp is steady.
• As soon as the burner kicks in the temp swings rapidly upward.
• When the burner turns off the temp drop rapidly.
• This YoYoing goes on for the duration of the roast.

What I'm not understanding is how the YoYoing is affecting the roast. With my UFO/CO there was a steady progression of heat in the bean mass. This progression of the bean temp was predictable and visible on the readout. With the Sonofresco it seems the beans are continuously being subjected to extremes in the temp range.

I'm thinking a roaster would work better with indirect heat. If the burner was heating up a heat exchanger chamber at least the bean mass would be evenly heated, not with a temp that's bouncing all over the place. Am I interpreting this correctly?

[peter]

Do you think the thermocouple might be reading more air than bean?

[Tex]

Do you think the thermocouple might be reading more air than bean?

That thought occurred to me, because the 1.4 lbs of beans are flying around pretty fast. Maybe a variable speed fan would help? I wondered why the RTD was placed so high in the machine.

[J.Jirehs Roaster]

I'm no expert but I roast on a sonofresco occasionally and I went through the same thoughts as you are so let me share my conclusions...

The air is cycling really fast in this roaster design so you will not get an accurate reading of bean mass unless you drill a hole in a bean and stick the business end of a thermometer in it... that most likely is why they read the temp on the down stream side, they simply profiled a good roast buy manual control and plotted the temps to their controller then decided when to cut off the heat for a given roast target. 

I think turning down the fan may be problematic for the burner but I never took it apart far enough to see the burner design so I am not sure...

bottom line is the only way to truly measure bean mass is to have a probe inside the bean... or more accurately a multitude of beans

[Tex]

I'm no expert but I roast on a sonofresco occasionally and I went through the same thoughts as you are so let me share my conclusions...

The air is cycling really fast in this roaster design so you will not get an accurate reading of bean mass unless you drill a hole in a bean and stick the business end of a thermometer in it... that most likely is why they read the temp on the down stream side, they simply profiled a good roast buy manual control and plotted the temps to their controller then decided when to cut off the heat for a given roast target. 

I think turning down the fan may be problematic for the burner but I never took it apart far enough to see the burner design so I am not sure...

bottom line is the only way to truly measure bean mass is to have a probe inside the bean... or more accurately a multitude of beans

I'm sure you're correct. There's a huge temp swing in air temps all the way through the roast, so I imagine that's being transmitted into the bean as well. I can't help but wonder what the YoYoing of temps is doing to the beans?

[milowebailey]

Tex

I've been down that same path....... I've measured temperature on that thing everywhere except your house. ... at the bottom of the roast chamber, inside the chamber at the bottom, middle, top and then where they measure it..... I still like to put the thermocouple approximately 2" off the bottom of the roast chamber.

If you look at the 1st plots of the Milowidget you will see the profile of the sonofresco in the roast chamber, and then I plotted them again above the chaff collector like Syd and Jerry's does it.  I use a thermocouple down in the bean mass, but it took me a while to find the sweet spot.  The temperature still varies, but once you get used to the roaster it will help you get more consistant results and allow you to stop the roast at a consistant point in between the pre-programed times. 

Also realized you really are measuring air temperature near the bean mass... which if you slowed down the air, your beans would not stir properly and you'd get burned beans on the bottom and not roasted beans on the top.  If you notice they use about a 15 second cycle with the burner... It never really changes much.   I've even tried rolling a ball of foil around the end of the probe approximating the mass of a bean.... but the thermal properties of the foil are different so it wasn't worth the pain to do it each roast.

My question is how often can I safely turn on and off the burner.  My theory is at first let it run for about 2 minutes and then see if on 1 second/off one second will work.  I figure once it's hot, it will burn a little more efficiently.

The method Coffee Kinetics uses measures the output temperature which is directly proportional to the bean mass.... with that said their profiles are based on the airflow, the total bean mass and the heat source.... if you change any of those the roast won't be constant using the pre-programmed profiles.

Try to roast 1/2 lbs.... it's almost impossible to roast that to FC let alone Vienna even at the 9 setting.  That's because you really have too much air moving past the beans and the control system thinks the beans are hotter than they really are.

Try to roast 1 1/2 lbs..... you will get burned beans on the bottom because the airflow cannot stir that large of a mass.

So the 1.2 lbs design was to get 1 lb of roasted beans every time.

My hope with the milowidget is to see if I can turn the burner on and off more often thus getting a smoother curve....


(note: Syd and Jerry, Coffee Kinetics and Sonofresco are all one in the same )

[peter]

I'm sure you're correct. There's a huge temp swing in air temps all the way through the roast, so I imagine that's being transmitted into the bean as well. I can't help but wonder what the YoYoing of temps is doing to the beans?

I don't think it's as much an issue as you think it to be.  If the beans are in fact roasting, their ability to gain or lose heat is waaaay less than the air in the roast chamber.  The beans won't be fluctuating as drastically, if at all.

[ButtWhiskers]

What is the flow rate (in CFM) of one of these babies?  I just had a really bad idea that will only cost me about $150 to try out (unless I burn my house down).

[CoffeeCarl]

I was wondering what would happened if you just turned the fuel pressure
down from 10 inches to 9 or 8. Would the cycling stop, would it still try
reach temp ?  Just a thought.

Carl

[milowebailey]

I've thought of that too.... not easy or inexpensive to do automatically...

If you just turned it down with an inline valve, it would just take longer to get to temp and with the profiles they have pre-programmed, I suspect it would not ever get to 1st crack...

But maybe worth a try.

[milowebailey]

What is the flow rate (in CFM) of one of these babies?  I just had a really bad idea that will only cost me about $150 to try out (unless I burn my house down).

Can't find the info, but when I open mine up for the Milowidget mod I'll see if the blower has that info on it.

Also spend an extra $10 for a good fire extinguisher

[Tex]

My question is how often can I safely turn on and off the burner.  My theory is at first let it run for about 2 minutes and then see if on 1 second/off one second will work.  I figure once it's hot, it will burn a little more efficiently.

I'm thinking that there needs to be multiple burners in the machine. One that's always on to maintain a minimum temp in the profile and others to boost the temps to the different levels of the profile.

With an electric heater you could just use a variac to control a single powerful heat source, but I just don't see a safe way to do something like that with gas.

As long as I have more questions than answers this will remain fun!

[milowebailey]

My question is how often can I safely turn on and off the burner.  My theory is at first let it run for about 2 minutes and then see if on 1 second/off one second will work.  I figure once it's hot, it will burn a little more efficiently.

I'm thinking that there needs to be multiple burners in the machine. One that's always on to maintain a minimum temp in the profile and others to boost the temps to the different levels of the profile.

With an electric heater you could just use a variac to control a powerful heat source, but I just don't see a safe way to do something like that with gas.

As long as I have more questions than answers this will remain fun!

I've googled control valves that have 2 setting... High and Low... but they are big $$$ unless I can find one on EBAY  most are used in boilers.  But even then the temp will go up and down as the burner moves from low to high and back to low.

I think Peter is correct.... the Bean will absorb some of the heat in the outer skin and when the heat turns off loose some, but also transfer some farther into the bean... what % goes where.... that's a good question...

[Tex]

Also realized you really are measuring air temperature near the bean mass... which if you slowed down the air, your beans would not stir properly and you'd get burned beans on the bottom and not roasted beans on the top.

I was thinking of the Poppery air poppers. The CW for using them is to add enough beans that the movement is slowed or almost stopped. If the airflow in the Sonofresco could be reduced enough to slow down, but not stop, bean movement, wouldn't more of the energy be directed into the beans? If so then it should be possible to get an accurate measurement of the bean mass temps.

Let me ask this to help clarify the problem: Where do you read the temp, as it YoYo's, to determine the roast level - at the top of the curve, the bottom, or some arbitrary point in between?

[Tex]

My question is how often can I safely turn on and off the burner.  My theory is at first let it run for about 2 minutes and then see if on 1 second/off one second will work.  I figure once it's hot, it will burn a little more efficiently.

I'm thinking that there needs to be multiple burners in the machine. One that's always on to maintain a minimum temp in the profile and others to boost the temps to the different levels of the profile.

With an electric heater you could just use a variac to control a powerful heat source, but I just don't see a safe way to do something like that with gas.

As long as I have more questions than answers this will remain fun!

I've googled control valves that have 2 setting... High and Low... but they are big $$$ unless I can find one on EBAY  most are used in boilers.  But even then the temp will go up and down as the burner moves from low to high and back to low.

I think Peter is correct.... the Bean will absorb some of the heat in the outer skin and when the heat turns off loose some, but also transfer some farther into the bean... what % goes where.... that's a good question...

So, you're in agreement with me then - a single hi-powered electric heat source would be more easily controlled?