Tag Archives: testing

Modified Thermometer Test w/ Rwanda Gkongoro Nyarusiza

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So as mentioned previously I took the thermometer probe and used one of those pipe cutters with the “wheel” for cutting things like copper pipe and sliced off part of the probe.  Due to the fact that this sort of cutter “crushes” slightly while it cuts this ended up making it so I could not slide the inner electronics out without fear of not getting it back in or damaging it (without having a soldering iron currently).  I instead slid all of the formerly connected probe upwards and taped it to the probe’s plug using electrical tape.  I then crimped the remaining probe in place at the top against the braided cover.

My initial test seems to have yielded a technically proper heat ramp based on what was happening.  Additionally the cooling cycle appears to have been pretty normal too.  It appears that when the cool cycle halts the beans are approximately 158 degrees and linger there while in the roasting chamber even when removed from the roaster.  They drop to around 130 degrees after being dumped out into another container within about 20 seconds and then they hang around 130-120 degrees for several minutes if undisturbed.

Here is my heat readings for a standard roast.  In this case I was roasting the Rwanda Gkongoro Nyarusiza.

Markers are A= Rolling First Crack, B= Second Crack.  Fan speed is shown as 100% for the knob being set all the way to the right.  50% is fan knob set in the middle position (straight up).

I was not able to keep track of any additional details due to manually tracking the roast on paper.  Cooling with fan speed increased to 100% starting at 6.1 was as follows:

Bean mass started at 120g and reduced to 102g for a loss of 18g or 15%

Problems with thermometer – YAY!

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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.

Temperature and the “pause” when pressing Up/Down button on FreshRoast SR500

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So as mentioned before there appears to be some sort of temperature sensing device built into the base that interacts with the Atmel processor.  There appears to be potentially power dimming circuits in there as well but I need a multimeter to verify all that which I do not have at the moment.

I’ve mostly been roasting the past few days “by sight, smell and sound”  the various coffees.  I logged some details on some of the coffees I roasted and they turned out ok when I brewed them but without temperature data to go with my timings I figured reporting the results was pretty useless so I stopped mentioning the other beans and what I roasted.

Initially my plan was to roast the coffee and see which ones tasted good or “bad”.  So far the only one that I have had any issues with is not necessarily “bad”…. but just not “really good”… it is only good.  That of course is a horrible horrible crime in the world of coffee.  [/sarcasm].   Even the “only good” coffee will be given a chance to redeem itself after reading the details provide on SweetMaria’s regarding the coffee and seeing if there are any nuances of needing to be darker or lighter or perhaps made into espresso or left for resting for additional days etc before I decide where it belongs in my ordering of new coffee for the “longer term” than the initial sampler.

I have now set up a digital gram scale (sensitivity 1.0g) with a small plastic measuring cup that I “tare” on the scale prior to pouring the beans in.  I’m finding that the amount is sensitive for only a couple beans that seem to roast “weird” compared to the rest where the others do just fine with a higher amount of beans.  These beans that are “weird” have little movement until the last 60-90 seconds of the roast.

The factory suggested amount is 120 grams while Tom @ Sweet Marias suggests 100 as being more realistic.  While I cannot claim to be any sort of coffee snob and certainly not an expert at roasting/cupping etc I’m finding the coffees I listed in my first blog…  by starting them on a completely level surface, and running the fan at 100% with the heat on low until a slighter amber color is achieved will result in pretty decent coffee with no more than one or two dark “spots” beans.  It seems on very small beans that apparently get stuck in the mesh before the fan starts.  They will end up scorching but the rest of them circulate quite well and explain why the “stirring trick” works due to this taking place while the fan is blowing.  Once you stir all the beans free from the screen they begin to free-float in the stream like the larger ones that never got stuck.  Everything else seems to roast gradually and without signs of burning though heavier beans will start to darken faster due to spending more time lower in the chamber.  I believe the roaster being level to be quite important as a result and starting off with a lower temperature and the “cool trick” artificially keeping the temperature low in the startup to help limit any burning.  This would side with people that declare a pre-heat cycle with the FreshRoast to be unnecessary since it would probably burn the beans worse than starting off slowly.  Ultimately a much lower temperature than “low” perhaps by around 100 degrees would be better as a “dry” cycle.

Today I managed to find a temperature probe in the grill section that makes it into the upper 400s Fahrenheit.  Most thermometers stop at 392 degrees or they have a lot of plastic that would prohibit you being able to have them near the heat of a roaster.  It is a BBQ grill thermometer made for Kenmore and was sold at my local Sears store.  It does NOT fit the roasting chamber without some convincing.  Convincing involves some very gradual bends being applied to the thermometer probe to allow it ot sit further down in the chaff collector putting the tip in the middle of the roasting chamber.  To convince it to turn I ended up utilizing the combination of a small gap on the rounded handle on a vise for some MINOR adjustments and the major adjustments being convinced with a large Maglight flashlight.  If you have ever bent metal electrical conduit you will get the idea.  You need to gradually support the pipe as it bends sit that it does not kink.  The temperature probe is actually a hollow shaft with a pointed tip on it.  The hollow shaft contains a set of twisted wiring that is actually a thermocouple.  It connects to the braided wire cover for that wiring which leads to the socket on the display.  You don’t want to kink the probe so it has to be slow bends in the probe to keep it from crimping on the thermocouple and potentially weakening things.

I have not roasted a batch using the new thermometer yet due to the fact some things came up today where I was not in the house and as a result we didnt really drink much coffee today to use the beans we’ve already roasted leaving me nowhere to place the finished roast.  As a result I now have a 2 day rest on most of these beans that are in there.  Today I get to see if the probe will pickup any appropriate temperature readings that match up with what would be expected at First Crack and/or Second Crack or if it is simply not sensitive enough and is actually picking up the roaster air only.

I have already attempted to run the roaster without beans for a brief time to inspect the temperature readings and see if there is any sort of ramp involved.  The temperatures did not seem to pass the mid 300s no matter what the setting while on high. Apparently with that level of airflow (if things are working with the sensor)  the heating elements needs to have back pressure from the beans in the roaster to reach the 400s.  As a result if running too small of a batch it will likely not roast properly thus never reaching a high enough temperature like too much beans could result in too high of a temperature being applied.  With the use of the Atmel processor and that possible NTC Thermistor Diode it probably means that the heater will cut out to not result in an overheat situation temperature wise BUT ultimately the beans in the roaster will probably burn without enough movement.

FYI the Atmel datasheet HERE shows that the processor has interrupt capabilties.  The buttons seem to be wired to two of the pins that have interrupt capabilties.  Due to there not being any chips to buffer the button pressing it would be my guess that the program made any pressing of Up/Downl to be an interrupt to the existing programming.  It seems to be part of the “Analog Comparator” which treats the status of two pins as a logical on/off.  If you press up it counts that button as pressed (1 or on) to the other button (down) as not pressed (0 or off).  It compares the two settings and initiates an interrupt.  As a result whatever signals being received for fan or heat control would be interrupted resulting in a “drop” to a minimum level that we are seeing.  This interrupt stops normal interpretation of the voltage in/out on the other ports and triggers a counter to go up or down.  There is circuitry built in apparently to do limited “debouncing” which is why holding the button does not make it continue to go up or down.  With the use of more expensive complex circuitry the variation in speed that we see would go away but due to cost savings this is a side effect.  The only way to eliminate such a pause is to use a different controller than the Atmel or potentially include extra chips to handle these changes.  The length of the pause is directly related to how quickly you can trigger the button.  I would suspect if you had “two bare wires” instead of the push button and you quickly tapped them together rapidly the up/down reaction would not be noticeable.  Due to the type of button used there is a long “click” in the button that makes the interrupt obvious.  The faster the contact and release of the button the shorter the interrupt allowing the circuit to continue on as programmed.

Inside the Freshroast SR500

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As I’ve mentioned it is my intention to try to improve on the control of the Freshroast SR500 by automating some of it with a microchip circuit.  I’ve got a lot of crazy ideas of things to do with this but most of it will take some time.

At the moment I’ve been unemployed for quite some time.  At my last employer I ran the IT department for a community bank.  That means I was in charge of the network, email, spam, spyware, virus protection, servers, desktops, printers, we had a Cisco Voice over IP phone system, and a variety of other things.  I got to deal with all the regulatory requirements from the Federal and State government writing policies, procedures, and supervising the IT staff as well doing budgets etc.  Anyway they outsourced the whole thing when the economy started getting bad probably because my salary and those that I would work with are not cheap and there were a lot of things that were changing and needing done.  Ultimately it was technically cheaper to just turn it over to a company that only does banks as an all inclusive package.  Since the economy has not improved much I’m still looking for employment which of course limits my funds to work on building control systems.  It does allow me a lot of time to work on projects such as learning to program microcontrollers.

Update July 2011 – Please check out my multi-part Teardown posting showing step by step taking apart a FreshRoast SR500 roaster after reviewing this post.

At this time I’ve written a significant amount of code that in simulators appears to operate in the proper voltage ranges and will turn on and off the heat and vary the speed of the fans.  Once I get the ability to start purchasing some of the devices and equipment necessary to build a prototype making circuit boards and programming the actual processors etc I will begin to blog about that as well.  For now I will write about what makes the SR500 work and my impression of what it does…

The Brain
Obviously the roaster has a fan, a heater, a roasting chamber, a chaff collector, a two number display, a switch, and fan speed knob.  What is not so obvious is what makes it work on the inside.  What you find inside are two circuit boards.  One has the knobs and switches connected to it.  The other board has all the power connections on it.  The control system for the knobs has what most people would refer to as “the brain”.  This is a 20 pin Atmel processor connected to a 12MHz oscillator running with about 2K of memory available to it.

Alternate view NTC Thermistor, ATmel AT89C2051-24PU

Next to the processor is a plug marked “NTC” where this is connected to a NTC Thermistor.  This is a type of resistor commonly used to test temperatures.  They typically have a narrow range of temperatures they operate in  but they are quite effective for the price.  The NTC is attached to some of the pins on the Atmel processor allowing it to sense temperature by measuring the electric resistance which changes with the temperature.

The NTC Sensor
Without knowing the specific NTC I cannot tell you how exact the temperature sensing is but while noticing that the switch has a high, medium, and low.   The temperatures listed by the manufacturer that it runs at are 490, 455, and 390.  These are 35 and 65 degrees apart from one step to the next.  This is a very large difference in temperature meaning it does not have to be very precise to tell the difference from one another.

The sensor is mounted in the path of the heater’s air.  You can see it through the grate at the top of the roaster.

NTC Thermistor mounting

As a result of the placement of the sensor this can measure how hot the air is coming off of the heater coils.  It does not get wired directly to power anywhere along the way.  Instead it connects directly to the Atmel processor which then feeds out to a MOC3043 Zero-Cross Opto-Isolators TRIAC Driver.

Left of High voltage board.

The MOC TRIAC is a special type of chip that isolates DC voltage from high voltage AC typically.  It often figures out when the AC voltage crosses zero volts.  In the US power runs at 110/120 volts and 60Hz.  Hz is a “times per second” rating.  In Europe the power tends to be somewhere in the 220+ volt area but at 50Hz… most parts in the roasting equipment are rated at either 400V or 250V so that it can be adapted to run using US or European (and other areas of the world) voltage without changing too many parts.  The Zero-Cross part of the chip helps to determine when the AC voltage goes from 0 volts up to +110/120/220/240 for example and then back down to 0 volts and then down to -110/-120/-220/-240 volts and back to 0.  That 0 to +volts  to 0 to -volts  pattern occurs 50 or 60 times per second or twice that when you just look at hitting the peak voltage from 0.  Effectively what happens when you try to “dim” the power (fan speed control, temperature control etc in some cases) it often is controlled with this sort of circuit.  In that sort of circuit (in otherwords) what happens is when you say run at 50% you let it go from 0 to +110 (0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110)  and then immediately slams it to 0 instead of rolling it down gradually (110, 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 0)  and then repeats it for the negative voltage.  Every time a MOC with Zero Cross connected to some TRIACs detects 0 point it gets reset and timing triggers occur to start over on the dimming at the appropriate points.

In the middle of the board are two devices that could be a TRIAC or a DC voltage regulator.  There are also numerous devices that could be TRIACS scattered over the board too.  The larger devices are attached to a large heat sink to keep them cool since they tend to generate a lot of heat.  Since I no longer have a multimeter to test some voltage I cannot determine whether the output of these devices are AC or DC voltage but there is obviously devices on here for creating DC voltage as well as those for switching and/or dimming AC voltage.

Fan, Bridge Rectifier KBPC606

This is one example of a place where DC voltage appears in the system.  Without being able to fully trace all of the wiring yet since this effort was only for a quick inspection and not to dismantle it I cannot see where this comes from and goes to but ultimately such a device (the black box) would normally take power coming in on two pins and through a series of diodes inside convert coming out the other two pins to DC voltage.  I am not sure where the fan knob (which connects to the two pins next to the MOC chip I believe)  is ultimately getting voltage from and whether it is AC or DC and if it is a lower voltage or higher one etc but it obviously controls some sort of dimming to this fan that apparently has AC voltage coming to the rectifier being converted to DC as it goes in.

Soooo… in the mean time I need to obtain a few things to get started….

  1. PIC Microprocessor and/or development kit – I have decided I will be using a PIC micro-controller for this project.  At the moment I am working on a simulated PIC18 but will probably move to a PIC24 and perhaps if I can get a development kit circuit board will use the new PIC32 to allow for some “additional” ideas I have for the roaster and perhaps some “accessories” to make it even more useful than “just” roasting.  I had started with a Basic Stamp 2 series microprocessor and quickly overwhelmed it quite some time back and then began learning PIC microcontrollers.  At this time I can only use a PIC32 if I can get a physical chip and board to work with.  PIC24 options are very limited in the simulation and will likely be a stage before reaching the PIC32 physical hardware.  If I can get the right development kit I can swap the PIC24 and PIC32 interchangeably on the development board.
  2. A lot of connectors similar to those used on the Fresh Roast boards pictured above.
  3. A replacement Multimeter since I no longer have mine… I had a rather substantial professional quality one but after several moves it was lost.
  4. A “rework” or “reflow” capable soldering system. These are typically used when prototyping SMD/SMT and high density chip based circuits.  There will be many miniature resistors and other devices that are actually soldered to the surface of the circuit boards rather than installed through holes.  Some of the communication types and chips for many of the sensors and devices require enough pins (or just that ultimately are not available any other way) that surface mount is the only option.  Many of these devices are extremely small and the simplest way of mounting them involves Infrared pre-heaters or hot air soldering and desoldering techniques.
  5. Real Time Clock chip.  Used for realistic good time stamping and tracking of the roast including the actual date for…
  6. Ethernet chipset and connectors. To allow a log tracking the roast information to be accessed from your computer including details form the …
  7. K or J Thermocouple and management chips to enable the PIC to know the various temperatures logging and responding to them from the air, the bean mass and other locations to control the heat and fan speeds as well as to…
  8. Display the results on a LCD Screen in real time to allow you to access a….
  9. Control interface such as buttons or touch device to configure the roast or select  a stored profile speeding things up or slowing them down or changing the temperatures etc in real time as well as access profiles or other details in
  10. Built in Flash memory or possible….
  11. SD Memory slot to transport profiles to the roaster or to archive them.
  12. Various power control parts such as TRIACs, IGBT, etc for phase control (dimming/speed control)
  13. PCB manufacturing materials such as photosensitive boards, chemicals, trays, transparency, etc…
  14. Small precision drill press to place any required through holes in circuit board too to allow “test” prototypes to be built
  15. PCB Vendor to produce a permanent solution once the prototypes are complete for me to transfer everything to since I need a couple of these for my roaster, my girlfriend’s roaster, and probably one for my landlord who is addicted to good coffee now and will end up getting her own eventually when I need to move out 😛
  16. Eventually I’ll need to figure out what sort of box to put it all in.

At this point I’m pretty confident I’ve identified all of the required actual components at least in general.  I need to finalize the power control requirements with a multimeter figuring out what all the actual roaster parts need/use and select those final parts and do some testing with lightbulbs and fans before I start connecting them to the roaster as well as do some testing of actual temperatures being put out by the SR500 as it comes from the factory.  Once those are finished I need to finalize the method of configuring the profiles using the final controls and display and I’m pretty much set.   I have not interfaced SD into the circuits yet but the communication systems are already there for other sensors.  The “file system” will be a bit of a problem programming FAT/FAT16/FAT32 into it due to some apparent Microsoft thing *makes rude gesture* so I need to look into that some more.

Theoretically I have a functioning controller in simulator.  It does not currently access AC voltage directly in the simulator though because I still need to determine the actual voltages being used to establish the amperage requirements of the various parts.  One area that is confusing is on the bottom of the roaster it shows 1600watts.  Well it’s a small fan and a heater coil and a TINY bit of electronics that uses less than an amp for that last part.  The fan seems to be deriving power from a plug marked 100W as shown in the “Left of High Voltage Board” photo.  Where the real problem comes in is with the heater causing the most concern.  You would assume the heater was 1400 or 1500 watts on its own with the unit showing 1600 watts on the bottom.  When you look at the board though….

1000W to heater coils?

Oh… and that device marked Q5 below it.  There’s a similar one next to it to the left.  That is one of the devices I have not determined exactly what it is yet.  There appears to be no identifying marks on it for a part number.  It might be creating DC voltage as a regulator or it could be one of many types of TRIAC.  The white stuff is a typical lithium thermal grease like the use on computer CPUs to make sure they don’t overheat by having a good thermal connection to the heatsink.  In this case some regulators depending on the voltage and amps or and pretty much most TRIAC dimmer devices generate a LOT of heat.  I’m thinking it’s a TRIAC due to the Q numbering being used since a voltage regulator typically uses a U number pattern.

Java Kajumas Organic Wet-Hulled Initial Roast

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Java Kajumas Organic Wet-Hulled Initial Roast

  • 7.0 to 4.3 – Minimal churn.
    • Low Heat
    • 100% Fan
    • 7.0 = Dark Green
    • 6.0 = Medium Green
    • 5.6 = Yellow Brown Green
    • 5.1 = Cardboard Brown
  • 4.3 Single FC – Low churn.
    • Set High Heat
    • Set 75% Fan
  • 4.0 – Chocolate Brown
  • 3.8 – Dark Chocolate
    • Set 50% Fan
  • 3.2 – Substantial FC pop
  • 2.8 – Rolling FC
  • 1.0 – End FC
  • 0.2 – Begin rolling 2nd cracks.
  • 0.0 – Automatic switched to Cool.
    • Cool
    • Set 100% Fan

Aroma: Initial aroma grass, popcorn.  24 hr aroma – Sesame Oil, Grass, faint vinegar.
Chaff: Extremely minimal.

Scoops: 3

Notes: For 4 scoops add approximately .5 to all times.

Fresh Roast SR500 First Impressions

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So as mentioned in the first blog I received a Fresh Roast SR500 roaster today.  I had been tortured by having coffee roasted in my girlfriend’s Fresh Roast Plus 8 while visiting her and then coming home to coffee out of a can and occasionally the whole bean stuff from the grocery store from my landlord that I rent a room from.  I brought a couple pots worth home after one trip to let me have some good coffee for an extra day or two as well as to introduce it to my landlord.

Like me she instantly saw how good it was compared to the usual stuff and she got interested in the process of roasting at home.  We watched the various videos on YouTube and reviews produced by those at Sweet Maria’s, Coffee Geeks, and a variety of other places.

The Fresh Roast Plus 8 that my girlfriend has and the Fresh Roast SR500 are both somewhat similar machines.  There is also a SR300 which is a less featured version (compared to the SR500) that is also available.  The Plus 8 and the SR300 are technically feature identical since both allow you to set the time only.  All three models have a specified number of minutes and then proceed to a “Cool” period at the end.  The SR500 has the addition of a switch to control the level of heat and a knob to adjust the speed of the fan.

Since I have only viewed an “in-service” Fresh Roast Plus 8 I cannot comment on the original packaging.  The SR500 arrived in a white cardboard box with various marketing type details written on the side.  Inside the box packed in white styrofoam was the SR500 roaster.  This includes a small manual, a small plastic scoop wrapped in a plastic bag, the roaster’s chaff collector, the roasting glass chamber, and the base.

Upon removing all of the parts from the Styrofoam packing I found all of the parts to have small little Styrofoam “dust” / pieces static stuck to the various parts.  As a result I needed to dampen a sponge and wipe off most of the parts or rinse them under a faucet (uhh no rinsing the base please… electric parts and water do not go together)…  Once everything was wiped down I then began to inspect all the various parts.

The Chaff Collector
This part of the roaster is significantly different than the Fresh Roast Plus 8.  I will start describing the Plus 8 and then moving on to the SR500.  The Plus 8’s top is entirely plastic with a screen inside the top part.  The top of the roaster slides down on top of the bottom part overlapping.  The plastic is entirely made from a high temperature plastic so that it does not melt.  It has a feeling of being somewhat light and somewhat inexpensive if not “cheap”.

The SR500 on the other hand also seemed to be a high temperature plastic and cosmetically looks slightly similar to the original Plus 8.  When you pick it up the top of the SR500 appears heavy and somewhat substantial in comparison.  The top is very shallow due to it no longer overlapping the base.  Here it is shown upside down…

The screen appears to be held in by a variety of metallic washers against small plastic “nubs”.

In the center of the lid behind the mesh is a 3 inch (roughly) metallic disc that appears to be similar to the metal used for bolt washers sold in the hardware store.

This provides a lot of bulk that appears to hold the lid on instead of allowing it to blow off.  More on this disc later.  The bottom of the chaff collector cup portion has a similar slotted opening over the roasting chamber to the Plus 8.  There is a sort of angled design to the slots that is different from the original Plus 8.

The top fits to the bottom with a small edge that appears very sensitive to proper alignment as well as proper creation of the plastic pieces when it is injected into the moulds at the manufacturer’s facility. The top piece has a matching groove on the inside to fit.

The top fits over the top of the roasting chamber… but not very well without some effort.  (Notice the gap on the right.  It takes some (minor) effort to get everything to fit snuggly)

The Roasting Chamber
The roasting chamber appears to be maybe 25% wider than the original cup if not more.  I have not measured it but this obviously has to do with the increased capacity of the SR500 from the previous roaster version.  The handle is held on similarly to the original roaster using a metalic band attached to the handle.  The handle on the new roaster is less solid feeling using much less material.  It also gets somewhat warm if not hot to the touch after a full roast.   In addition the metallic base is made from much thinner material… the same as the band on this roaster.

The last base was a thick cast metal base with a glued in round hole screen.  The new roaster has a base that is all one piece pressed from material that appears to be similar to the previous screen.  This results in a less robust feel to the roasting chamber.  I would postulate that this lighter material at the base, however, helps in the cooling cycle by having less metal mass to hold heat near the beans at the end.  Further inspection of this base shows it to be very shallow compared to the last roaster.  The old metal base was much deeper than the current base causing more of the beans to be “hidden” during the initial part of the roast on the old roaster but also allowing the cup to be more firmly seated in the roaster base.

The Roaster Base
Now on to the base…  This is where the most substantial differences are.  The old roaster was perfectly round with a knob that you turned to set the length of time or slide it to cool.  With the new roaster you have a digital “up” and “down” button to increase the time in .1 minute (6 second) increments.

When you start the roaster it starts with 6 minutes immediately dropping to 5.9 on the red LED display.  On the SR500 you start the roaster by sliding the switch to Low, Medium, or the High heat setting.  You raise and lower it by pressing the up and down buttons and can force it to cool by pressing the cool button.  This switches the heat element off into a cool mode running the fan only.  The fan sound is significantly different than the previous Plus 8 roaster.  It is of a different sort of pitch and seems quite loud compared to the Plus 8 though I cannot be sure without running them side by side one after the other. Unlike the SR300 which has only one fan speed the SR500 has a variable knob.  Lowering the fan speed to the middle position on the knob it seems possibly similar to the old roaster.  Due to the much wider base of the roast chamber to accommodate more beans more air is needed to churn the beans.

The wattage on the base is listed as 1600W for 120V.  The model number appears to FB102SR.

Roasting
This roaster seems to thus be more sensitive to being on a solid, level surface.  I have seen several people complain that it does not churn the beans enough resulting in burning.  In the instructions it says to run the beans (if necessary) initially by using the low heat setting with the fan on high.  What I found with an initial roast is that this is an important step until you see significant movement.  With my surface being very level the beans initially had good movement similar to that found in the Fresh Roast Plus 8 and an acceptable churn when set on low heat with high fan.  As the beans began to turn amber in color I then switched the heat to high.  It took approximately 1.5 to 2 minutes for the roaster to reach the amber coloration and the beans to begin to have a more rapid churn.  Once the heat was raised to high I allowed the beans to continue to roast eventually lowering the fan speed to around the half way point until first crack was reached.  At this time I slowly increased the fan until second crack and returned the fan to high during the cool cycle.

One of the drawbacks to the current configuration is you need to purposely remember to return the fan knob to high when you go into the cool cycle.  Otherwise the configuration seems to work well enough as is.  I think this model would be somewhat confusing for a first time roaster for them to figure out what to do and when in response to the roast.  It seems (from other reviews) that the SR500 has a higher fan output than the SR300 at the high setting and my used middle setting being the standard speed on the SR300.  I would consider that to be critical / mandatory making the SR500 the suggested model and thus making this tougher on a new person.  New people should concentrate on running the roaster on high fan and low heat until they see color changes happening as described or a lot of height in the beans being moved.  Once that happens they can dial down the fan speed and increase the heat to get a roast going.

Regarding the smoke from the roaster I have perceived this to be similar to the smoke from a Plus 8 roaster even with the increased capacity.  I didn’t set off the smoke detector but it is pretty obvious you’re roasting coffee inside the house.  You do want to run an exhaust fan while roasting typically with either roaster but it is not significant amounts of smoke.  The roaster does seem to cool down somewhat quickly MOSTLY.

Dealing with the finished roast.
As I mentioned earlier I was coming back to the chaff collector.  Due to the metal disc in the lid of the chaff collector there is a significant amount of heat retained in the lid for a much longer period of time.   This makes dumping out the chaff collector somewhat difficult right away meaning you need to let it cool for a while.  Due to the increased capacity of the roasting chamber you have more chaff collected up top.

The change in the angles of the strainer in the chaff collector do not appear to make much difference in the chaff passing through to the collector.  Most of the chaff appears to stick well into the collector, however, and you end up with similar amounts of fallen bits of chaff on top of the roasted beans that need to be blown out if you do not wish to get any excess in your grind. This roast typically only had a thin ring around the edge in the first picture which is now completely blocked up possibly due to the extra capacity.

The cooled beans are lightly warm and seem to be a few degrees cooler than the Plus 8.  This is possibly due to the cool cycle being digitally timed rather than controlled by a physical timer knob on the Plus 8.  On the Plus 8 the knob does not have any sort of positive confirmation that you are in cooling or heating as you turn it so sometimes you might short the cooling cycle a few seconds while with the SR500 (and 300) you will always have the same cool cycle by pressing the cool button.

At this time I have some beans resting in an airtight container until tomorrow after my initial roast attempts.  These roasts were done “by eye/ear/smell” and later in the week I will dig out my scale and try to get “scientific” about this as I work through the various sample coffees.  For now I just need decent FRESH coffee rather than the swill from a can.