Roast times on a 15kg Ozturk

[Bradleysteenkamp]

Hello,

I've managed to run about 6 roasts through our newly acquired Ozturk 15kg roaster. Really enjoying using it and have installed my own bean temp probe at a lower position in order to log some curves using the free Roast Logger software.

I've managed to roast as little as 2.5kg with no issues at all, lovely even roasts.

Today I put the biggest roast yet into the machine. 11kg. As expected, it was the slowest roast so far and took about 22 minutes to get to the end of 1st crack. This was with the gas running at full and the airflow at about 50%. Just wondering if this is normal for a roaster of this size? The smaller roasts I've been doing have been finished at around 15 minutes (mid way between 1st and 2nd crack).

It's a cast iron drum roaster and I'm not entirely sure how I should be playing with the airflow control! I'm finding that opening the airflow more than 50% will cause the burner to cut out, almost as if it's blowing the flame out!

To speed up a roast should I be looking at roasting with the airflow value more open or more closed?

Any advice would be greatly appreciated!

Thanks
Bradley

 

[eldub]

Do you have a temp gauge for the air in the roaster drum?

It doesn't sound like the roaster is getting hot enough. Are you sure the gas line is providing adequate fuel? How many inches of gas are you getting?

 

[expat]

Bradley, glad to hear you've solved your propane problems and are up and roasting. We have an Ozturk 10k and a 10k batch of beans takes about 22 minutes with the air at 70 for us. I know time is money but is it bad to have a 22 minute roast? We've been very happy with the results of the longer roasts.

By the way, how'd you solve your propane problem. Did you find a Novacomet 29mbar regulator? Did you find a good service person?

 

[eldub]

Isn't that (a 22 minute roast) more in line with baking the beans than roasting them?

 

[Bradleysteenkamp]

Hi Expat,

Thanks for the reply. I tried a different regulator, also a 37mbar and that seems to be working out fine at the moment! I'm actually getting as little as 25mbar during the roast on the gauge on the machine so it might not be quite enough.

One thing that I think might have slowed my roast down yesterday is that I dropped in with the drum temp display showing 165 degrees. Perhaps I need to go a bit hotter for the drop?

I tried the roast this morning and it tasted great so I'm not too worried! My only concern with the long roast was the impact it might have on the flavour but the proof is in the tasting!

I've found that if I open the air up to 70 the flame goes out so perhaps I need to look at a way to get my pressure closer to 30 as it's a bit on the low side!

Must say I love the machine so far, I'm getting nice even roasts on it. I could never achieve that on our small 1kg machine!

Thanks
Bradley

 

[Bradleysteenkamp]

Eldub,

thanks, it's got an exhaust gas gauge showing the temperature of the air as it leaves the drum. My pressure is showing 25mbar during the roast, the manual states 30mbar so perhaps it is a bit on the low side!

 

[eldub]

Bottoming out at 165* seems a bit low to me. I shoot for between 200 and 230*. How hot are you getting your roaster pre-drop? (For a full batch I get ours up to around 420* before charging the barrel with beans.)

 

[Bradleysteenkamp]

165 was C which would be 329f so it sounds like I dropped in way too low. I roasted a 6kg batch today and dropped in at 180c (356f) and that roasted nicely but is a small batch for the machine. Next time I run a bigger batch I'll try dropping in at about 420.

How do you tend to work the airflow valve?

 

[eldub]

I drop small batches (8-12 lbs.) at 360* to 380*F, depending on how many batches have already been roasted that session.

Maybe try somewhere around 215C for a full batch.

How far down are your temps going after putting the beans in the roaster? (As I said above, we shoot for 200-230*F)

 

[expat]

Bradley, for what it's worth on a cold machine we heat up to 175C (actually that is Ozturk's factory recommendation for our 10kg roaster) and drop the beans. Once roasting The Lovely & Talented Roast Mistress will drop them all the way up to about 190C if the previous roast went really high temp, as some beans will, and she doesn't want to wait to cool things down back to 175C. But she's now got hundreds of batches of experience and in the novice stage she'd always bring it back down to 175C.

Eldub said maybe drop at 215C. To me that is a really, really, really high temp--to drop them at or even to roast them to.

In other threads on this forum I've seen a lot of temperatures mentioned as a drop temperature or a final roast temperature but they are always much higher than the temperatures we work with. I'm sure one reason for that is that every roaster is different. But you also have to factor in that you've got a cast iron drum roaster and Eldub, and I'd venture to say most other roasters on this forum, are working with a steel drum roaster. I've got to think that that's where the wide variances in the heats they recommend and the heats we roast with come in--because we're all turning out a good product. There are significant differences in thermal dynamics between cast iron and steel.

Back to the 215C recommendation. To show you how hot we consider that, the safety on our cast iron drum roaster is set to turn the machine off at 215C. We've never run a roast that high. I think 207C was about the top. This is why I tend to think the difference in steel and cast iron is the key here as I know Eldub has roasted a lot of beans and those temps work for him on his roaster and people are lining up to drink his coffee.

As said earlier, every machine is different, so you'll just have to work with your roaster and find your own 'sweet spot' and I hope the temps I've given above for our cast iron roaster help you to some degree (sorry, couldn't resist!).

 

[eldub]

expat: I'm of the opinion that your machine isn't showing temps accurately. (Not saying you aren't turning out a nice product.)

First crack takes place around 385* F no matter what the barrel is made of, imo. That's a scientific fact, imo. hehe

 

[eldub]

Here are a few links to sites giving information on bean temp phases....


Coffee roasting - Wikipedia, the free encyclopedia
Sound is a good indicator of bean temperature during roasting. There are two temperature thresholds called "cracks" that roasters listen for. At about 205–207 °C (401–405 °F), beans will emit a cracking sound much like popcorn does when it pops, only much quieter. This point is called "first crack," marking the beginning of light roasts. When the beans are at about 224–227 °C (435–441 °F), or a medium roast, they emit a "second crack."

https://www.sweetmarias.com/library/content/using-sight-determine-degree-roast

Coffee Roasting - CoffeeResearch.org
Stop the roast somewhere between the end of the first crack and less than half way through the second crack. Do not roast well into or past the second crack. We recommend a roasting chamber temperature somewhere between 205-215°C.

As you should note above, Coffee Research.org recommends a roasting chamber temp of between 205-215*C. I like to keep my roaster at between 400 and 415*. When I make the conversions, my temps are almost exactly in line with what the org above recommends. Beans in our roaster also reach a rolling first crack at around 400* (I hear the first signs of first crack at 385* as I mentioned above.

No offense, but the temps are off in your roaster. It has nothing to do with cast iron vs stainless steel, imo.

 

[expat]

You know what Mr. Eldub, you may be onto something there! I'll have to check my temps against another meter and see if, in fact, I am getting bum temp readings. Thanks for the reference research!

 

[Bradleysteenkamp]

Hi guys,

thanks for the replies! The temp difference is an interesting point, I've installed a thermocouple probe and have noticed the temps are quite different to those shown on the machine during the warm up stage. While warming up the thermocouple is showing about 15-20 degrees higher than the machine probe!

still, despite this I'm getting nice roasts that so far are tasting very good.