Posted Sun Feb 9, 2014, 9:05am Subject: Toastess TCP-713 Insufficient Heat
I have new Toastess TCP-713 air popper and the unit doesn't seem capable of reaching a roasting temperature. After a few attempts to roast that resulted in failure, e.g. roasting for 25 minutes and never reaching 2nd crack, I placed a temperature probe into the chamber during which time the maximum temperature reached was 395 degrees Farenheit. This is a new, stock unit, I have performed no modifications.
I've monitored the chamber temperature while roasting (using 75g of green beans), as well as with an emtpy chamber, and regardless the maximum temperature never rises above 395F. I'm curious to know what the expected maximum temperature should be in a stock air popper like the Toastess TCP-713?
Posted Sun Feb 9, 2014, 12:00pm Subject: Re: Toastess TCP-713 Insufficient Heat
Welcome to Coffeegeek and home roasting Ray.
Air poppers are designed to pop popcorn and so the tolerance for temperature control is not nearly so critical as roasting coffee. If you bought 3 of these identical and probed/tested them, you would likely see 3 very different results. It is good you got a temperature probe in there to get an idea what is going on, and 395F is not so far off the mark. Bean temperatures around 400F are usually required for first crack, and air temperatures of around 450-460F are needed to keep the roast moving to finish in this type of roaster.
Here are some things that may help:
Adding more beans will slow the air flow and this will raise your temperatures. Although the additional beans would seem to take longer to roast, it is the higher air temp that will speed up the roast.
The ambient air temperature has a large effect on these air roasters. It's winter here so ambient air temps are lower and this may be part of your problem. I think 60-70F is a good ambient temp for unregulated popper roasters.
The thermostat may be turning off the heater element in your popper. If this is the problem, it will require modification to disable it. Signs that it is the thermostat are that your temperature will oscillate up and down and you can usually hear the fan speed up and slow down due to the change in current draw of the heater as it cycles on and off.
There are hundreds to thousands of posts here about how to get a reasonable roast from an unmodified air popper; tilting, stirring to regulate air flow, extension cord to lower temps, putting it in a box to raise ambient temps.... and on.... Spend some time digging here to get some ideas.
Posted Sat Mar 1, 2014, 8:55am Subject: Re: Toastess TCP-713 Insufficient Heat
Thank you for your reply to my question about the temperature in the Toastess air popper. I followed your advice and used 100g of green beans on my next roast. As you indicated, the temperature hit 400 F in less than 5 minutes, and by 6.5 minutes it was at 430 F (and didn't get any higher during this roast session) where I began to hear the 2nd crack. I pulled the plug at 7 minutes, and thought I hit the mark for the Guatemala Projecto. It seems though that I might have kept roasting for another minute or so, as I'm unsure if I really achieved a Full City for a majority of the beans.
The time between 1st crack and 2nd seemed too brief... I will roast another batch today and record my results to see if I can hold the roast time a little longer, and see if the temperature gets closer to 450-460F as you indicate. BTW, I roast in San Diego, and the ambient temp in my garage is in the mid-60's.
Posted Sat Mar 1, 2014, 12:26pm Subject: Re: Toastess TCP-713 Insufficient Heat
The 450-460F I mentioned above is for the air temp coming into the roaster, not final bean temp. (450 bean temp in my popper would be well into second crack, black & oily)
It's great to have the BT probe, but soon will become frustrating when you see things go wrong and are powerless to adjust it.
Here's the best advise I can give based on many years of air roasting in a poppery 1.
Think of the roast in 3 phases:
1. drying, (free moisture heated to vapor phase) The bean temp up to around 300F (internal bean temp is well above 212F as it occurs under pressure), beans are yellowed but (hopefully) not browning. grassy/hay smell.
2. Ramp to first crack. Browning occurs, toasty smells, and the 'bulk heating' of the bean mass from 300-400F. If the drying was even and well paced, browning will occur quickly and evenly. If the beans become uneven with splotches of green and brown, you have gone too fast through the drying. (....or not enough stirring/mixing of the beans)
3. The finish or development phase. From start of first crack until you finish the roast. First crack is the marker for internal bean temperatures of the 'development phase'. How fast, how hot, and how far you run this part of the roast is most critical and sensitive as the roast reactions occur fast at these temperatures in the roast.
To get started in the right range, I recommend you try to get each of these phases in the range of 3-4 minutes. Total roast time then would be in the range of 9-12 minutes. The shorter times will tend towards brighter(then 'greener'), longer towards softer(then 'baked').
A BT probe is a good thing to have, but ideally it would be better to also have a probe at the bottom of your popper that measures the heater air just before it hits the beans. Just like roasting in an oven, you set the oven temperature according the what you are cooking, then monitor your roast progress with the 'meat' thermometer. It's obviously important to get the right oven temp to get the right roast on a prime rib. So much more important when roasting coffee as it happens fast and the ideal temperatures are fairly tight.
If you had control of the roaster air temp, ... here's what I would recommend to start:
Preheat to 300-325F range for 5 minutes. Add beans and start roast timer.
At all times during the roast, the air temperature must always be higher than the bean temperature. Never let the beans loose heat during the roast. (if you switch the heater off during the roast, it can only be for fractions of a second to adhere to this rule!)
How much higher the ET must be above BT will depend on how fast you want the roast to progress; the greater the difference, the faster the bean temperature will rise. As example for phase 2 from 300-400F in 3-4 minutes would require the BT rise of 25-33F per minute. In my poppery 1 this would mean the ET is 50-70F ahead of the BT.
The final finish ET will depend on how dark you want the roast and how long the finish. For City+ to Full City+ ranges, and 3-4 minute finish, this would have my Max ET between 450-465F. (all these numbers will be somewhat different for different probe placement.)
Obviously you would need to have a knob on your heater to follow this profile recipe.... One thing that helps is the air temp is very sensitive to flow rate; By tilting the popper and letting more air out, the temperature can be reduced. You will find that the popper will get too hot too fast esp. towards the end of the roast where the least amount of additional heat is needed and the beans are most delicate to abuse. Tilting the popper during the finish to control the max finish temp will help.
To simplify, Try to get the drying phase ET around 300-325, (without heater control, it's best to start cold, no pre-heat) Keep ET ahead of BT as drying heads into ramp to first crack. A smooth rise in ET from 350-460F during the ramp phase for 3-4 minutes. Hold finish ET at 450-465 until the beans are done.
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