How to achieve consistency?


I have been making my way through a lovely Mexican which my friend used as an espresso roast at his roastery.

I roasted 4 batches last week and after tasting them knew what to do in order to move the roast in the direction of tastiness. I eagerly booted up my Bullet today and began roasting.

For context, the weather today is noticeably colder than last weekend. It’s overcast and about 2-3c cooler. I started my roast with the intention of elongating the roast overall. I was dropping P at earlier temps as a way to do this. My curves were lining up with the roast from last week, but I was reaching Yellowing and 1stC more quickly despite the lower power input. Charge temp was the same, and my green has been stored in the same spot so I expect minimal temp change there.

As I was roasting I dropped my charge temp by 5c and this helped. I also dropped P at cooler temps as I went through the roasts to achieve what I wanted. After 3 roasts later I managed to get the times that I was after.

This seems wasteful and I would like to know better how to predict such changes in how a roast would behave for consistencies sake. Has anyone experienced something like this before? And does anyone have any tips on how they manage their roasts when they are running more quickly or slowly than intended?

Thank you in advance!!

Not sure if this helps but…

I always put a target roast in the background using Overlay. To reproduce the same flavor, I try to match the IBTS temperature curves. A good effort yields curves that overlay to within about the width of the curve (just a few pixels). The preheat, power, and fan settings to achieve this of course vary with ambient conditions, which is probably the root of your question. But I roast indoors under the range hood, so not much of an issue for me. I do try to bring the green beans up from the basement a day in advance to warm them up to room temperature for a little extra consistency.


I think @bradm has your answer i.e. you’re getting sabotaged by your roasting environment. Keep in mind that when you set Power the Bullet manages that setting (nearly) independent of the room ambient- the Bullet is not managing temperature, just power. And I suspect even that is affected to some extent by ambient temp and line voltage variations. So the heat from the drum lost to the environment will vary depending upon these ambient conditions- temp and line voltage.

I believe the easiest way to manage variations in ambient is through Preheat. I’ve never tried to develop objective settings for Preheat when Ambient changes. In fact, all 3 variables you have at your disposal (Power, Fan and Drum) will have impact on the profile as the ambient varies. Without that correlation there are going to be variations in the curves and time during a roast. It’s more complex than I can manage! So I just up the Preheat if the shop feels pretty cold (confirmed by a temp/humidity meter). Not much I can do with Preheat about ‘too hot’ in SE Arizona but I do have a portable swamp cooler for the worst days.

Like Brad I’ve found the Overlay helpful in trying to manage temp profiles. For my roasts (and the profile I use is atypical of what most here want), time is going to vary. I don’t notice huge variations in taste as a result as long as I manage drop temp (always the same) and do my best to keep the slope of temp curves similar to the Overlay.

As a point of reference, I roast in an insulated work shop with no ambient temp control- the best I can manage is a space heater set on Low; yeah, it has a thermostat but any measure of temp control is an accident. The ambient temp was 61° F when I started last Thu and about 72°F when I finished 3 hours later. If you’re outdoors it’s going to be harder than what I’m doing.


ps- I record temp & humidity for each roast.

Thank you for your replies. I understand what you are getting at.\

However, I guess my main point is how can a roast be considerably faster in a colder environment when all of the Bullet parameters are the same? This is what I was experiencing and would like to understand more. Thanks.

If there was a significant difference in humidity on the hot and cold days, maybe this could have adversely affected the heat transfer on the hot roast?

This was a thought of mine, unfortunately I don’t have a humidity meter, but I have seen that they are cheap and I will invest in one for sure!

Right now I just look up weather for my postal code to get temp and humidity. It sure would be nice to get that data for the environment right around the roaster though.

Warning- way too much info about a weather app. But maybe it will help with forecasts nearer your location…

Try this free app for Android phones. I suspect there’s an Apple version but… ?? It tracks your location or if you’re uneasy about tracking you can enter city, state. It will do ZIP codes too but for my purposes a ZIP code is not specific enough for my location (85602 is over 100 sq miles; Benson is about 7 sq miles). In addition I was able to drop a pin to adjust for my location within my city, state forecast. The latter works to the extent their model has enough variation to have more detailed info, otherwise it’s just the named town.

The back story: The app is labeled as being from channel 18 in Lexington, KY but is created by Weather Channel. It works pretty much anywhere in North America. I’m an RVer. In 2010 we missed a tornado by a small margin. We were lucky but the scarey part was we hadn’t a clue we’d had a close call till we watched the local evening news. We realized we needed something that could announce weather alerts for our current location as we are driving and Storm Tracker does that for your current county. (which can cause a gap as you leave a county with no alerts but drive into one that has an active alert). For your purposes, Storm Tracker gives detailed forecasts (temp/humidity/wind speed & direction) either daily for 10 days or hourly for the next 48 hrs. Plus it has radar imaging. I suppose there are times the alerts (which override everything on your phone) are a PITA but generally it’s not an issue. And yes, it’s a free app.