Time to preheat... Question

So, I’ve roasted for a while. 1lb batches with repeatable results with the same beans. Well, this past weekend I changed a variable on accident. I let the roaster preheat for 45 minutes or so. Typically, its ready to go after 20-25 minutes.

The resulting coffee is NOTICEABLY more flavorful (with the same recipe) and more of it extracts as espresso (dark stripes in the pull last longer).

Anyone done much study on long preheat times vs roast as soon as possible?

There have been discussions about this in the past.

There are a number of people on the forum that let the first preheat of the day run longer to let the Bullet build up and store more heat.

Some people will run a less critical roast or sacrifice the beans of a first roast to allow the Bullet to store more heat.

In the past, did you run the same roast/beans twice? Did the second roast come out better?

Ambient temperature where the bullet sits can be a factor in how long to preheat.

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I agree, that the bullet says too early “the bullet is ready”
My 2nd roasts are always better than the first roasts on the same recipe.
Could you guys grogram a better preheating cycle, which fully loads the thermal capacity of the bullet? Wasting one batch should not be an option.
Maybe as an option for hobby roasters like me, where time is not super critical.


Currently when the preheat cycle starts, the Bullet turns on the power to P7 and maintains that power until the preheat temperature is reached. then the Power is adjusted between P1 to P3 until the temperature is stable at the preheat setting. The Bullet then maintains the preheat temperature for about 10 minutes and then will prompt you to charge the Bullet with beans.

Here is a link to a preheat cycle that I saved so that I could analyze it:

The Bullet will continue to hold the preheat temperature for a period of time AFTER the CHARGE prompt and that time is programmed into the firmware. I am not sure what that value is. But I believe that it is over 45 minutes. After that times out and there have been no beans added, the Bullet will go into shutdown mode.

What would be nice is to have an option where there would be a check box and time field on the starting page of the roast profile where we could specify an additional amount of soak time for preheat. For the first roast, you would have the check box selected and for subsequent roasts you could uncheck it.

I believe that their is a lot more going on in the firmware regarding preheat because when I am doing back to back roasts, the preheat soak time is not 10 minutes after the just finished roast. It can be less than 10 minutes.

For my first roast of the day, I start a timer on my smart phone set for 15 minutes after the Bullet starts prompting me to charge.


for a while now I have been preheating to 300 deg c. then resetting the preheat to the temp I want and letting the temp drop to it. This has helped my first roast to be more consistant with followng roasts

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This is probably a lot quicker than doing an extended Preheat.

Plus a long preheat never really gets to the same place as the first roast of the day. If you have beans that are ready to be tossed you can do a throw-away roast but that’s often not an option for a home roaster.


I do 10 minutes but that’s my workflow as well.

In a discussion with Scott Rao, he commented that the Bullet is one of the highest conduction roasters he knows. The beans in a Bullet are roasted more with conduction with heat transfer from the drum walls rather than through convection with the hot air within the roaster. According to Scott, conduction roasting results more in “roasty” tasting coffee while convection roasting leads more often to better tasting coffee.
Following this logic, extending the pre-heating time probably results in higher air temp within the roaster, for the same drum wall temp, which increases heat transfer to the beans through convection, resulting in better tasting coffee.
Just a theory but worth testing out.

Interesting about increasing convection heating thru longer preheat. Not sure I agree about how this immediately relates to taste as I suspect it has also to do with duration of the roast (that from someone who roasts pretty dark).

But I can confirm (for my purposes!) that extending the preheat is important for what I enjoy. I guess it’s all about learning to get the best out of the roaster that’s available: “don’t blame the tools; blame the workman”.

About 3 years ago (more?), @quartzglen recommended doing a throw-away roast to get the Bullet thermally stabilized. He had a source of out-of-date beans for that purpose, but I don’t. So I’ve used an extended preheat as a substitute since reading his preferences (that and the not-universally-popular heat soak).

I think Rao raises an important point: the Bullet is not a direct replacement for a large drum roaster.