Coldest ambient roasting temperatures?

What follows is just my personal opinion. YMMV…

The Bullet can be significantly affected by the ambient, especially the first roast of the day. As a practical limit I choose to roast when my shop temp is 60°F or higher, and less than about 90-94°F. Easily achieved in the insulated shop as I can add a small space heater in the winter or I can turn on the roll-around swamp cooler. But roasting outside doesn’t allow you to add/remove heat very well. I’ve done it but it is limiting. But then I live in Arizona and don’t have to deal with what you see for winter temp swings in Denver.

The Bullet spec doesn’t address this directly:

  • Operating ambient temperature: Tested for use at room temperature (25°C)

… which unfortunately isn’t an operating range.

My Bullet has operated fine at the temp extremes mentioned above. It’s just that the roast profile isn’t exactly the same thanks to temperature loss thru the side walls and face plate being less than optimal. If you rely on exact timing in your roasting, it’s going to be a challenge as it will take longer to get the same BTUs into the beans when the temps are low… you just can’t fool Mother Nature.

The effect is that the operator may have to tweak the power, fan & drum speed to compensate for differences in heat loss thru the sidewalls & face plate. Using the limits I mentioned above I don’t have to make any changes in the profile (profile = the power/fan/drum-speed settings vs. time and/or temperature) after the first roast of the day. HOWEVER- I may see roast time at each setting vary significantly during the roast.

Preheating will be a bit of an issue with respect to the Bean Temp probe. That probe is mounted to the face plate so there is heat loss from the outer shield of the probe into the initially colder face plate. After the first roast the outer surface of the face plate will be hotter (be careful- it gets hot!) and the measurement error caused by the colder face plate will be less. IBTS is less affected by the face plate temp changes (the sensor is pointed at the drum interior). During a 2-4 hour roast session you’ll see a change in the separation of the IBTS & bean probe temp curves.

If you’re roasting the same greens most of the time it will be well worth your time to develop a Recipe. When switching varieties during a roast session, however, a single Recipe may not serve. Differences in moisture content and rate of moisture loss can make a one-size-fits-all Recipe out of the question.

As I said above- just my opinion: YMMV.


Thanks for the reply Bruce! You make several very good points. Since there really isn’t any good guidance on this, I can only rely on the anecdotal experience of this community, which is why I began the thread (unless I get really lucky and garner a reply from one of the brothers :wink: ).

A good buddy of mine has had an R1 for about a year, and consistently roasts at temps in the low 40’s in the winter (CA) without any major issues. Certainly ambient temps can affect roast progression if the roaster settings are kept constant. I feel like there should be enough flexibility with this roaster that tweaking settings should be enough to still produce a good roast with low ambient temps.

In my case, generally the only time I’m going to be roasting the same beans time and time again will be for espresso blends. Otherwise my roasts are typically going to be one or two roasts, and the bean is gone, not to be seen again. I will likely develop my own “standard” profile over time like I had done with my old Poppery, and tweak fan/heat (and drum with the R1) settings to maintain roughly the same profile between winter/summer conditions.

I could likely build/setup a powered vent hood in the garage and roast in there in the winter, but it still gets down into the 30’s even with a small electric/oil heater running when it gets extremely cold outside.

If you’re handy, you might build a small coffee roasting enclosure in the garage out of used office cubicle panels (frequently available real cheap) with either a panel or a polyethylene sheet (old shower curtain?) ceiling that would be much easier (and cheaper) to heat.

Comfort for both the Bullet and you!

With some creativity and a few hinges, it could be collapsable so you can fit the car in between roasts.

  • Gray

:worried: I really hope that’s not necessary! :grimacing:

I think he may have mentioned the electronics getting quirky at low ambient temps, but I’m not 100% on that. He definitely mentioned that low ambient temps would make the roast profile change dramatically, but it seems like you could compensate for that with higher heat.

Here’s where Jacob provides some specifics: Colder climate and roasting in garage or shed - #20 by jacob

Thanks for the link @john_l ! :slight_smile: :+1:

Ok, so if the limitation is the electrolytic caps not liking being cold, then theoretically, I should be fine roasting in the cold IF the machine is stored indoors(around 70F), and then brought outside or into the garage and started right up.

@jacob can you provide any further insight?

TIA! :muscle:

Congrats on the new roaster purchase! You won’t regret it!
I’ve been roasting on the Bullet v1 for almost two years in Alaska. The roaster is set up in the garage that is kept at 55 degrees, and I roast with the garage door open to vent out the exhaust.
The only issue I’ve ever noticed is when it is 20 degrees F or lower outside (which is 7-8 months of the year), the Bullet will not say “Charge” when it is up to preheat temp. I just have to watch the display to know when to add the beans.
Other than that, I roast away with my puffy jacket and hat on while sipping coffee!
Best wishes!

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IIRC, deciding when the Bullet has reached Charge temp is a combination of the IBTS reaching (and maintaining) the PH temp and the bean probe reaching a certain percentage of the PH temp.

Because the drum is inductively (directly) heated, it reaches temp fairly quickly, which is shown by the IBTS temp. However ,the bean probe temp more closely reflects the air temp inside the drum and, because it is mounted to the face plate, the face plate temp. These (and other bits and pieces) are much slower to warm up because they are heated radiantly from the drum, and to some extent convectively by the air in the drum as it is heated by the drum.

These also affect the amount of heat the bean sees when it is charged, which is why the bean probe temp is part of the equation in determining the Charge temp.

In your cold Alaskan garage, it will take quite a bit longer to get that faceplate up to temp, especially as it is also sucking a certain amount of cold air in during PH. I expect, that if you waited longer, it would eventually reach the Charge temp.

In my 70°F dining room, the first roast may take 15 minutes to say Charge after the IBTS temp has reached the PH temp. Subsequent closely timed (but not quite back-to-back) roasts reach Charge much more quickly because the face plate and the other bits and pieces are already pretty hot. And subsequent roasts proceed a bit more quickly, as well.


I have to admit, I am a little bit surprised by what I have been reading about the face plate and bean temperature probe “cold soaking”. I would think that once the roaster has been pre-heated, this would not be much of a problem. I certainly wouldn’t think that the bean probe would be thrown off by the face plate being colder than the roast chamber.

I roasted yesterday evening in my old West Bend Poppery 1. It was 28F (-2.2C) outside, and this is an air roaster. It is constantly sucking in ambient air, heating it up, and cycling it through the beans. It has ZERO problems roasting in these conditions despite this supposed “limitation”, WITHOUT any need to preheat. I still can’t fathom how a drum roaster like the R1, which is much more isolated from the ambient environment, can’t keep up in the cold… :confused: :thinking:

@jacob I hope I can get your input on this! TIA!!! :+1:t2:

Yes this is true. Just keep it warm enough to be able to start up, after that you should be able to roast in -20C if you want.

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Awesome! I appreciate the reply @jacob ! THANK YOU!!!

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Just my experience only having the bullet less than a week.

Last night I finished my seasoning roasts and then I roasted a pound of Brazilian and Kenyan Peaberry beans afterwards in my garage. It was 31 degrees Fahrenheit outside according to my watch with a decent wind. I had the bay door fully open and my propane heater on to help me stay warm (to stand next to occasionally). It took the bullet about 30 minutes to preheat but didn’t have any issues roasting when I got into it.

Just my experience from Western NY and our mild winter this year. Usually it’s a lot colder all winter long.

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My Bullet is out for delivery. I’d really prefer to be able to do my first roasts during daylight, but that won’t be possible until Sunday. :frowning_face: Might have to do my seasoning roasts in the evenings after work. :man_shrugging:t2:

I feel ya! Mine arrived last Friday and I couldn’t start any seasoning roasts until Sunday night. Then finished up Tuesday night seasoning the drum & did two roasts to drink.

Unfortunately with work and the family schedules I Norma can’t roast until the evenings. I hope to roast this weekend during the day for a change and get a nice pipeline of beans.

I’ve been roasting in my garage in Westchester County NY for the past 2 1/2 years. I try to limit my roasting to ambient temperatures above freezing, however, I’m sure one can go lower with some caveats about quality or modifying roast profiles.

Here is what I do.

I start preheating with the garage door closed and with a space heater pointing towards the front of the roaster where the input draws in air from the environment.

Beans are kept inside at indoor temperature (68-72* F) until I am ready to charge.

When the roaster is fully preheated plus a bit more in winter (30 minutes minimum even if the charge “command” is flashing) I open the garage door and bring out the beans. I also place the space heater closer to the roaster and aiming at the air input opening. My goal is to heat the incoming air the best I can to minimize cold air stalling a roast. I think most or many gas roasters preheat air through the flame so the bullet is I believe especially prone to air flow cooling. Charge the beans and roast as usual.

Subsequent roasts may have a fully warmed machine but the cold incoming air is still an issue if you use the fan to help to control your roast. I think the heater helps when roasting in the garage.

Hope this helps.

Well, I couldn’t wait lol… :rofl:

After thoroughly checking over the machine, I decided to try a seasoning roast of 1 pound (450g). Machine was at 70°F (21.1°C), I took it outside into the cold and dark, and immediately started the warmup.

Ambient 28°F (-2.2°C), 80% RH. Preheated to 446°F (230°C).

Preheated for 25 minutes before the machine said it was ready. I let it go for 10 more minutes.

Started the roast. Drum at D9, heat at P7, fan at F4. Took 6:30 to first crack, ROR around 20-22 the whole time once it stabilized from the beginning. Adjusted to P5 and F5 and took it through second crack (9:30; I purposely spread this out), finishing it at 466°F ITBS temp (241°C).

Finally, I dropped power to P0, upped the fan to F9, and let the beans agitate until ITBS had dropped to about 375°F (191°C). Then, I initiated the cooling cycle and dropped the beans.

At that point, I thought, “What the heck?” and hit F1 to start preheat for a back-to-back roast. Wound up doing 3 roasts (all 1 pound) back-to-back.

The only thing that really changed from one to the other was time to first crack dropped to 6:15 by the 3rd roast, second crack coming at 9:15. It also warmed up slightly outside to 31°F (-0.6°C).

My BIG takeaway here? I don’t think I’ll be having too much trouble using this machine to roast in the cold. :sunglasses: :+1:

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I understand about the “I couldn’t wait” :+1:

A couple of things as an FYI:

Some Bullet roasters have noted that their roast recipes and playbacks produce different resulting profiles when the ambient temperature is different and you may have to adjust your roast as the ambient temperature changes.

During the summer months, you may notice that the PCboard temp gets hot enough to force the Bullet into a cooldown mode in the middle of a roast. A number of us have added an external fan blowing at the belly of the Bullet to keep the shutdown from happening. Aillo has made modifications to the firmware updates to address this issue. There are a number of threads on the forum about this.


Fortunately, because of the inductive drum heating, the Bullet moves far les outside air than most roasters, so, while outside air temp will affect your power/time to milestones (and time to preheat), it doesn’t have as much affect as with many other kinds of roasters.


Grey- I’m certainly open to being shown that I am wrong but I disagree with your comment.

I’m under the opinion that airflow is controlled by the fan independent of the heating source be it inductive or gas flame. In many gas roasters, the air is directed through the flame to preheat ambient external air. In the bullet, fan and airflow is cooling and moving outside air is a function of fan speed… The colder the external roasting environment, the more effect on a profile.