Scorching, Tipping, and Roast Defects

It’s natural to use higher preheat temperatures with larger batch sizes, but is it possible with our machines to preheat too high and create roast defects like scorching, facing, and tipping? I’m particularly sensitive to this possibility after watching Rob Hoos’ interesting webinar on roasting defects (tipping discussion begins at 31:00):

This recent roast of Sumatra Aceh Gold “Mutu Batak” was the first time I’d ever noticed what might be some tipping:

https://roast.world/@bradm/roasts/rqgyBl7tV33b0oPj9p-W2

Here are some of the beans, 10 days post-roast, stored in a 1-way-valved container. The ones at the top of the picture may have some tipping - tiny dark spots only on the upper ends, and one other near the top may show some facing:

According to Rob’s webinar, this relatively soft low-grown bean could be susceptible to tipping. Then again, the dark coloring may just be some residue from the traditional sumatran processing which happened to stick to the tips of those few beans. The roast color is generally pretty irregular, many other beans have dark areas elsewhere. I’ve used this profile on a few other beans without issue. And the brewed coffee tastes great, pretty closely matching the description from Happy Mug.

What do you think? Was a 20 minute preheat at 240C too hot for this bean? Will try slowing the roast down a couple of minutes next time to see what happens.

This also makes me wonder if there is any correlation between bean density and the bean’s ability to handle, or not, higher PH and/or roasting temps. I have yet to measure density of my beans but Mill City does talk about it in one of their videos.

It’s hard to distinguish possible tipping defects from the photo, as the beans are so dark. You might try to pull a few beans from the tryer at one minute intervals and take pictures like Rob did in his presentation.

I did actually use the tryer during the roast because of Rob’s comments that some scorching is no longer visible by the end of the roast, and you’re absolutely right @coffee_mook the tipping was more obvious earlier in the roast. Some of this is also my limited iPhone photo skills as the beans look much lighter in hand than in the photo.

As far as corrective actions - either lower PH temp or lower power during the first minute…

FWIW - I did find I am using the tryer more with the 500g roast. Even at the lower PH temp I started with I saw a little bit of scorching and uneveness especially in the beginning which made me think of lowering the D to D8 or even D7 so there is a bit less contact with the drum wall (higher centrifugal force would result in more contact).

The Rob Hoos video was a good learning tool.

I’m wondering if preheating as we do on the Bullet makes beans susceptible to these roasting defects because the induction system (I think) heats the drum to PH temperature first and the rest of the roaster heats up later on as we wait for the charge command. The BT probe readings never catch up to the drum temperature IBTS measurements. Bullet users I believe use higher PH temperatures than gas roaster users where the temperature on their BT and ET probes are used to mark charge time.

Correct me if I’m wrong but if a gas roaster charges at say 380* F that 380* is the temperature of both the drum and the body of the roaster (where the BT and ET probes are located). If we PH to 380* on the Bullet our BT temperature might be 250* tops when the charge command is heard. That difference may be where we have to adjust our thinking when comparing strategies for roasting. Do we use lower PH temperatures but wait an hour until the BT and IBTS measurements are closer? That might allow lower PH setting and drum temperature but quicker than normal roasts at that PH setting due to more thermal energy in the whole roaster.

Thoughts?

I thought I heard Rpb say that he generally doesn’t see tipping on the Bullet due to the even nature of the induction heating the drum vs the gas burners on a roaster creating hot spots…

1 Like

@blacklabs for my 1KG roasts, D9 passes on less heat than D8 or 7. Of late have been using D9 from Charge to Turnaround, D7 till 135℃ and D8 thereafter. Gives me a lot of momentum for preventing FC related crashes…