Level: Apprentise

Reading time: 8 minutes

I’m having some roasting trouble and would love to hear your opinion if you get a chance to respond. I’m using a Klarstein air fryer (1400w) to roast 1kg of beans at a time. 
One difficulty I’m having is how much variation there is in my temperature readings. I stir the beans and use a digital thermometer, but they can range from 110˚c to 130˚c. I guess there’s nothing that can be done about this. Would using a bigger roaster (e.g. a converted chicken rotisserie) give me a more even temperature, because there would be more tumbling? Should I reduce the amount of beans in the basket?
I’m taking a mental average as best as I can throughout the roast, then at the end I’m trying to make sure the minimum temperature reading is reaching my EOR target of 125˚c. I just don’t have much faith that my ramp calculations have any consistency, due to how variable these temperatures are.
Also I’m having issues with bitterness. I just made a few batches: Peru, Honduras, India, Columbia. All but the Colombian taste bitter and lack complexity. For all the roasts I’ve been attempting the same thing: setting the fryer at max temp (230˚c), holding it there for the first 4-6 mins, then dropping the temp to try and hit a ramp of around 4˚C in development and around 3˚C in finishing. Normally this means I’m reducing the temp to say 190 after 5 mins, the reducing again at around 12-15 mins. Sometimes this means the ramp slows too much so I increase the temp again.
I’m just losing faith about the accuracy of my ramp measurements and my ability to control the roast; as well as creating consistent profiles I can repeat.
Any tips or advice would be greatly appreciated. 
In terms of the bitterness, do you think it’s likely I’m ramping too hard? My roasts are a bit frantic at the moment… maybe I should try dropping the temperature lower and keeping it low throughout?

I want to start off saying that it sounds like you are doing most everything correctly and just what I would do so it sounds as if there is just fine tuning to do.  For those of you that are not familiar with the Klarstein it is basically like the Gourmia Convection oven.  

You are absolutely not ramping too hard.  That is exactly what I recommend.  Start at the maximum the oven will allow and then back off.  Make sure you are pre-heating enough so you are not wasting time and energy trying to heat the beans and oven at the same time.  5 minutes should be sufficient.

What is does sound like you are doing is braking too much in that later leg.  You don’t say exactly how low you go but I would not drop under 160 C or 320 F at 12-15 minutes.  

I and others have found the same thing about erratic temperature measurements in these slow rotating turbo ovens.  Dropping down to 2 lb might well help the mixing and give you better consistency.  I found the best way to reproducible roasts is by taking the lower number and always measuring in the same spot.  I like about 1/3 up from the spot closest too you.  Sure, some of the beans are warmer but many of the inner ones are cooler and that seems to even out just fine.  This also matches to the amount of power available in the oven.  Beans can only heat up so fast with 1400 watts and the lower number appears to be the more accurate one.

It is worth noting I am using an infrared thermometer.  I am not sure what you mean by digital per se because the digital is the display, not the thermometer.  I would be hesitant to trust a probe thermometer since you have to keep the cover open too long to get an accurate measurement.

If the roast is slowing down so much you have to increase the temperature again then next time you just need not turn down the temperature so far.  This is really the whole purpose of taking detailed notes so that you can learn from the past and not repeat your mistakes. 

It is hard to diagnose an issue with bitterness, especially when you only list counties of origin and not specific beans.  I have 6 different beans from Peru and 5 from Vietnam alone and they are all pretty different.  And it could as easily be your recipe or an over sensitivity to bitterness.

If we go ahead and assume the bitterness is a roasting artifact I think it may well be resolved with continuing to power through the roast as I describe above and not stalling.  The stalling does not so much create bitterness but keeps other flavors from developing and if you are getting a high bias temperature reading then you may not be roasting as aggressively as you think you are.  That will also keep other flavors from developing as much also.  

It is possible to ramp to hard and create bitterness but I’ve not yet see a small electric roaster that is roasting 2 lb or so that can do it.  There isn’t enough power available.  Aside from that you should be able to smell it if you are creating bitterness.  There will be a very pronounced acrid aroma and sensation when smell them.  If that is absent, as I expect it is, then you fine.

Turning the heat back up after the drying phase can indeed cause scorching and bitter flavors.  This means the ramp should ALWAYS be decreasing as the roast progress once you pass out of the drying phase. Before then you can adjust the heat massively since the moisture will cushion any abuse you heap on the beans.  

You are most likely only going to make matters worse if you turn your roast ‘long and low’.  Manage your ramp by not cutting power too early and that should help a lot.  That said, again due to what seems to be a high temperature bias reading in these turbo ovens I do find it is advantageous to allow the beans to mix and stir an final 5 minutes or so at your EOR temperature once you reach it.  This will give the appearance of an extra long finishing phase but it really isn’t.  Just make a note when you hit your EOR and then go another 5 minutes.