Preheat temp advice?

Hey all - new guy on the forum here. I’m about 120 roasts in on my Bullet and loving it but just now getting on the RoasTime train. I roast 1kg almost every batch and have set my PH temp to 419 F each time. My roasts are taking anywhere from 14-15min from dumping in the green to emptying into the cooling tray.

As I’m looking through roast curves and data from others on this forum I’m seeing many have a higher PH temp…between 450 and 500 F. I’m assuming a higher PH temp will shorten the overall roast time. But from a flavor standpoint, what are the pros and cons to starting with a higher PH temp? I’m wondering if I’m missing out on something.

Thanks!

joel

@aillio_user23 - Yes, a higher preheat will shorten the roast for a given size batch. For taste effect, nothing beats experimenting. I think I taste more acidity from a shorter roast carried to the same final temp but you may not agree (I am not qualified to compare PH vs. flavor emphasis).

You’ll probably find as many profile preferences here as there are users. It’s my impression that most seem to follow Rao’s recommendations (Scott Rao: “Coffee Roaster’s Companion”, “Coffee Roasting- Best Practices”). Nothing in his writings is directed at a small-capacity roaster like the Bullet, but there are enough similarities to capture the attention of most users. There’s also Rob Hoos, “Modulating the Flavor Profile of Coffee: One Roaster’s Manifesto” who has done seminars directed at the Bullet (though not covered in his book). There’s also the 1996 book “Home Coffee Roasting” by Kenneth Davids. All of them pop up easily in a Google search.

Bruce

Thank you for the feedback and recommendations!

I started with a 310℃ PH for my 1KG batches. That left very little headroom for the roaster. Have dropped down to 300℃ now. I get the Charge command when my BT is around 195℃ to 205℃.

For a brief period, I was using a fan below the PCB enclosure at the bottom for keeping the PCB cool. My BT at Charge was about 10℃ higher. This was giving good momentum to my roasts and my roasting time was shorter but found my coffee sapped of almost all aroma.

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Hi Cash,

Can I ask how long it takes for you to get from pre-heat to charge at 300C? After 20 minutes I am manually putting my machine into charge mode with a pre-heat temperature of 226C (500g roasts). Despite the machine being at 226C for at least 5 minutes, it is not automatically going into charge mode. When I was pre-heating to 200C it would typically switch to charge at about 10 minutes.

Thanks

You may need to wait longer. Besides getting Drum Temp (IBTS) readings at the selected Preheat (226°C? that doesn’t sound like a selectable value in f/w preset), BT has to be stable/settled and above a specific temp (sorry- forgotten how it’s calculated). Takes more than 5 min. after reaching the Preheat setting. The intent is to reach some thermal stability prior to adding beans and BT will continue to rise after Drum Temp is at the target.

Bruce

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Hi Bruce and thanks for the reply. I may actually have it set to 230C since I use fahrenheit and it is set to the temperature that is recommended in the documentation for a 500g pre-heat. My real concern was that after 15 minutes it still did not go into charge despite my assumption (probably incorrectly so) that the system had stabilized. I need to stop being impatient and simply let it go for a good 20-30 minutes to see if it will go into charge mode automatically. Appreciate the feedback.

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If you’ve chosen C° in the PRS setup, preheat increments in 5C° intervals starting at about 195°C or 200°C (?); if you’ve chosen F° then preheat increments in 9F° intervals based upon the C° starting point. [Conversion C° <–> F° is a pain. If I’d just bite the bullet & join the rest of the world the pain would go away; but… ].

If you look at the graph while preheating, Drum (IBTS) Temp will stabilize fairly fast then oscillate around the set point (probably on the high side). BT (at least in my case) will continue to increase with a more and more shallow slope. That slope (again in my case) will continue to drift higher for a long time. I let the Bullet stabilize for nearly an hour to get the highest BT starting point I can because…

When doing back-to-back roasts the Bullet will go to Charge quickly. The associated BT for the second roast will be substantially higher than the starting point for the first roast. At least one user here uses throw-away beans from a local source to roast a batch that he tosses, then he goes into the first ‘keeper’ roast of the day.

Are you using f/w 562? I don’t think f/w has changed in the recent past (3 mo? 5 mo? dunno) but what I described above is with f/w 562; worked the same in preceding f/w 558.

Bruce

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With preheat settings between 190C and 230C, I get “charge” in about 9 minutes. I have f/w 553. Perhaps the algorithm for deciding when to announce “charge” changed in later f/w releases?

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My roaster is about 4 months old and I checked the firmware yesterday which came back as up to date. I believe it was 562. I suspect my issue was simply assuming things had stabilized. When I was running smaller roasts with a lower pre-heat, it did automatically go into charge mode relatively quickly. While I do not have enough data to support my theory, I get the impression that the higher the pre-heat setting, the longer it will take to go into charge mode per degree. In other words, getting to 200C…pretty fast. 210C…could take a fair amount longer. Going to 220C is going to take considerably longer than getting to 210C. The last 10 degrees will always take longer than the previous 10 degrees. I know that is likely confusing.

I agree- the higher preheat setting the longer it will take to stabilize DT & BT. Ambient temps also get involved… takes my Bullet noticeably longer currently with the colder temps in my shop. Also power line variations can get in the way. Anything involved in getting heat into the drum.

Bruce

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Takes about 24+ minutes the first time. Thereafter between 5 to 9 minutes in subsequent pre heats.

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I most often preheat to 230C…after many roasts, I’d agree 24 minutes is about average. If I hear charge before that, which is rare, I assume an error, and toggle through the PRS button quickly to PH to “finish” the preheat.

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Cash and Wingsprd, thanks a ton you guys. This is super helpful. I will definitely be more patient and let it run a good bit longer.

I’m about 120 roasts in R1 V1.5, FW 558. I generally preheat to 300°C and rarely do back to back roasts. Being the impatient person that I am (just ask my wife) I often load my greens as soon as IBTS reads 300°, failing to wait for the “charge” notification. Until today, I haven’t even considered letting the Bullet stabilize before adding beans.

So today was a roast day. Ambient temp about 10°C, humidity 48%. 1K roast, preheat to 300°C. When ITBS reached 300°, BT was 160°C. At 28 minutes BT reached 186°C and I got the Charge announcement. I waited 3 or 4 minutes then started roast which went smoothly. I didn’t notice any difference between this roast and my “impatient” roasts but we’ll see how it is in the cup tomorrow morning.

Jerry

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Well you guys were spot on! My PH temp is set to 230C and while the machine first hits that temp at around 9 minutes, it took almost exactly 23 minutes for it to fully stabilize and go into “Charge” mode automatically! Really appreciate the guidance, without any reference point it was very difficult to know how long it should take. Being a bit on the anal retentive side, it is awesome to know that everything is actually working as it should.