Posted Thu Jan 27, 2011, 10:59am Subject: Thermocouple Equipment for roasting.
I had a few people send me emails asking about my thermocouple setup.
Thermocouples aren't difficult. You need something to read a thermocouple (aka a thermocouple meter), and the harder part is getting a thermocouple source that can supply the thermocouple you need.
Type-K thermocouples have the temperature range you need, and the miniature connector is fairly common flat blade with one larger than the other.
My reader is a Cole-Parmer model 4232CP (or EW-86460-03) Click Here (www.coleparmer.com) , it runs on a 9V battery and reads temp in Deg F. It actually comes with a thermocouple, but I'm unsure how high a temperature the insulation for the thermocouple will last. Haven't tried it yet, but I imagine it will work for a while.
Cole-Parmer also has thermocouples that are more suited to contact with oven/roaster type temperatures: Click Here (www.coleparmer.com) is one example. You'd have to talk to them to figure out which one would work for you, depending on how you decide to go.
Through a friend of mine, I bought a $25 Temprel T21-MU-24K-AI, http://temprel.com/t21-28/ it is 24" long, and is made of 0.062" bendable wire that I secured by wrapping it around the drum pivot, with an Inconel sheath. I've got a request from Temprel for a half-dozen more of these, I expect them to be on the order of $18-$26 each.
I imagine that either 205-341 0.062" dia x 18" long $25.50 or 205-344 0.062" dia x 36" long $27.70
Be careful - you only get one bend at any point in the wire - straightening it back out will most certainly break it.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
The thermocouple reader is listed around $85 but goes on sale regularly for around $45 + reasonable S&H. The Tenma 72-7712 (shown) not only has 2 inputs but also has good (manual) temperature correction and collects data into your laptop (unlimited) or stores 100 points within it for downloading later.
Also shown are a source of type K thermocouples sheathed in stainless-steel, designed for kilns etc ...but just perfect for coffee roasters. I have 3 of them and others here have bought them too.
No, its not flexible. But if you did, to what advantage? You would know the environmental temperature but you could not vary it at will. The Behmor has profiles but not adjustments, other than time.
I had read about folks opening the door after first crack to slow things down before second. Not the most effective way to control temperature but it apparently gets the job done. At least, when it's too high.
Posted Fri Jan 28, 2011, 7:24am Subject: Re: Thermocouple Equipment for roasting.
I looked at some of the rigid steel probes. I was looking for something that didn't interfere with the door, was not permanently installed, and did not require any modifications to the roaster (it was only a few weeks old when I started taking temps - I didn't want to start hot rodding my brand new Behmor).
For me, it was worth the extra $10 to use bendable wire. 0.062" seems to be a good tradeoff for rigidity and formability - I bent it around the pivot but it can slide off if I want to remove it. The probe tip is about 5mm from the rotating drum near the bean mass (between the chaff tray and the drum), and it formed well to the roaster edge and doesn't interfere with door opening/closing nor the seal. I think any thinner and I might be dealing with positioning issues and lack of position stability, any thicker and I wouldn't be able to form it.
@JKalpin: I like the logging feature of the reader, and saw that same one (or similar) in my searches. I was looking for something no more than forty or fifty bucks, so when I saw most of the logging ones ranging from $85 on up, I gave up on logging ones and figured I'd be more involved if I jotted the temps myself every 15 seconds. What can I say, I'm an engineer - which is to say that most of the time I'm "cheap". :)
(btw, cheap is relative - I'll spend more on quality equipment, and do things manually if it saves me money - plus I wasn't sure the thermocouple idea would work or even matter, so I didn't want to sink a Benjamin on something that didn't work...)
I was actually really surprised when I saw consistent results. On P2, I did a batch of my India Giri-Estates that turned out beautifully - the temp reached 410ºF right at the first tick of 1st crack, 15 seconds just after the elements began cycling. I did a 2nd batch of same that hit 1C about 10sec before P2 power drop and 402º. Both of those 227g batches worked very well - each batch had a 2.75 minute 1st crack with 45 seconds separation between end of 1C and the beginning of 2C - where the temp stayed at ~400º the whole time.
Then, I had the near-disaster of a batch of India Giri-Estates that got to 386º before the element began to cycle (mis-pre roasted, oops!). If that happens, 70% power is not enough power to maintain development of the roast (it hasn't gone exothermic yet) so I watched helplessly as the temperature gradually dropped over the next 3 1/2 minutes by about 15º.
Thankfully, I heard 1C just near the end of the 70% power band - and the power increase helped finish the roast through the end of 1C plus 30 seconds. The result was a surprising mix of cinnamon-nutmeg flavor, a hint of something tangy or winy (blueberries? raspberries? orange?... I'm still figuring it out) fairly light and much brighter than my other darker roasts of this same bean.
Point is I knew exactly what was happening, and also saw that my pre-roast (from the thermocouple) was miscalculated (because of that DARN COUNTDOWN TIMER - that thing changes if you hit the + or - buttons!!!! LOL).
My pre-roasts are now both time AND temperature - with an emphasis on the temperature. I try and make sure my pre-roasts are about 2-3 minutes long, but reach 200-210ºF as close as I can get it. I find that much of the variance from there to 1C is taken care of by being consistent with a temperature pre-roast. In other words, if I see a difference at 100% power same bean in 1C times from the start of the roast, INCLUDING the pre-roast, about 90% of the variance is between ambient and end of pre-roast - from 200º to 1C seems to be consistent for any particular bean within 15 seconds.
The other thing a thermocouple is good for - the "door opening" method of temp control. You can use the door opening AND the thermocouple to essentially do a P2 type of profile - by monitoring the target temperature and opening and closing the door to maintain a temperature, you'll be much more consistent if you're doing it to keep the temp at a certain level. I'll lead it by a few seconds, then juuuussst crack the door to slow the roast about 10º before my target temp - works really well.
I wouldn't be able to do either of these things (know what went wrong/use workarounds to control temps) without a thermocouple - and yes, I'm rockin' it old school with my little pen and paper and my hashmarks for crack noises... but hey - ya gotta do what works for you, right?
It's like flying using ded reckoning and compass vs. plugging your flight into a Garmin 530 - I feel like doing it manually keeps me sharp. (yep - also a Pilot, but that's a MUCH more expensive hobby)
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
Posted Fri Jan 28, 2011, 12:02pm Subject: Re: Thermocouple Equipment for roasting.
I will point out that BehmorThing has a decent interface for manually logging temperature and while it's still called BehmorThing, all of the Behmor features can be turned off and then it works quite well for all other roasters. And it's free, but only Windows.
Posted Fri Jan 28, 2011, 12:41pm Subject: Re: Thermocouple Equipment for roasting.
Thanks, Ira. I see that and I really like BehmorThing - only problem is my wife doesn't like me taking the laptop into the garage or heaven forbid outside in light snow (yes, I have roasted some really good batches in 4ºF weather and other times in light snow... LOL).
What do you mean "...while it's still called the BehmorThing..."?
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
Posted Tue Feb 1, 2011, 8:57am Subject: Re: Thermocouple Equipment for roasting.
I got a quote back for 10 Apollo Thermocouples set up with inconel sheathed 18" length 0.062" wire with an 8" braided steel lead and yellow flat bladed miniconnector. $23 each, or $230 for a lot of 10.
More than I was hoping for, but still in the ballpark of what I was expecting.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
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