GDM528 wrote:doubling batch size seems to result in about a one-step reduction in roast level

This has triggered a minor crisis-of-faith in how I'm measuring the roasting process. The temperature profiles were identical, yet I got different results - yikes. Measuring temperature of the spinning bean mass still strongly correlates to the roast level - it's necessary but not sufficient. It'll be interesting to figure out what's missing.

For now, I'd consider the batch size to be a fine-level roast level control 'knob': increase=lighter / decrease=darker.

Iowa_Boy wrote: The idea of using Kapton tape is really tempting, as I think that may help a lot.
I know it's high temperature, but is it considered food safe?

Ironically, many foods aren't considered to be 'safe': bacon, fried chicken, glazed donuts...

Kapton isn't certified as food safe - but it's not considered toxic either. I decided that I'd rather have Kapton tape in the roast chamber, than the fiberglass insulation that's typically used for thermocouple wire. I'm also not gonna fret too much about the aluminum surfaces the beans are rubbing up against during the roasting process...

mgrayson wrote:I roast 75g every time. It reduces one variable...

Genius strategy sir! Depending on your mood, or drift in the bean's behavior, you can fine-tune the roast results just by tweaking the batch size up or down.

Legend_217 wrote:Now I wonder if rapid change in temp is the reason for scorching ? My non Ikawa beans were all scorched

Exactly which recipe were you using? I can run a temperature sweep and check for overshoots. I have noted that many of Ikawa's recipes start the roast with a really violent spike in temperature, usually to get to the browning phase quicker (less worrisome), but some of their profiles spike all the way up to first-crack temperatures right from the get-go (more worrisome).

I've haven't seen any scorching effects with my non-Ikawa beans - but I only run smaller 50g batch sizes, which keeps them levitated off the bottom of the chamber during the roast.

Iowa_Boy wrote: The second thing I noticed is there was a distinct ROR crash right around first crack.
Looking at the temperature profile, the generic profile has a declining temp right around first crack.

Agreed, Ikawa's recipes seem to overreact to the exothermic phase. My current recipe for natural-processed beans only drops the temp 5C over the span of 1 minute. My temperature measurements show the bean-mass temperature is perfectly flat during that period. And I got a noticeably better-looking roast with a 5C drop versus a 10C drop.

I ran some tests:

Greens: Guatemala Antigua Santa Inez B300 from Sweet Maria's.
Profile: Generic Washed Espresso Medium +++ (Ikawa's recommended - I beg to differ, but that's what I used.)

I did two 50g batches to see if the machine warming up mattered. Here are the results: Batch size followed by Espresso Vision Score (I used about a teaspoon of beans - much more than usual - to do the measurement) Higher numbers are lighter.

50g, 23
50g, 22
75g, 21
100g, 23



These all get labelled "Medium-Light". To give you an idea of the scale, 25 and up is light, 16-19 is Medium, 14 is Medium-Dark, under 10 is Dark.

I'm a bit surprised by the uniformity, but not by 75g being the darkest. The bean motion seems sluggish and uneven at 100g, although I don't know what effect that SHOULD have on the roast level. Oh, First Crack times were consistent with the above measures. And the development times were quite short (1:15 out of 8:30), so the "+++" moniker is laughable for this combo. This is NOT an Ikawa bean, but I have a lot of it lying around .

Now this is ONE experiment with ONE bean and ONE profile. Further research is necessary!

mgrayson wrote:I roast 75g every time. It reduces one variable...

70 to 75 range works great for light roasts

I was roasting 2 100 gram batches of one of the supplied beans to espresso, the first one I watched closely and it seemed like beans got stuck in the middle. So for the second one I edited it slightly to raise the fan speed. No idea how much as it's hard to tell but the second batch was much less likely to have a single bean remain at the top middle and the roast seemed a bit more even. Did lose 2 beans in the chaff, but I don't consider that a problem. Watching it, I'm tempted to make a one turn spiral of some sort to try and raise the beans spinning against the wall and increase agitation. Maybe 12 ga copper as I've got lots of that.

Ira

mgrayson wrote:Greens: Guatemala Antigua Santa Inez B300 from Sweet Maria's.
Profile: Generic Washed Espresso Medium +++ (Ikawa's recommended - I beg to differ, but that's what I used.)

After staring at the different batches you roasted, to me it looks like the leftmost cup (50g?) is the most uniform, and the rightmost (100g?) is the least uniform. I think you have to grind up the beans to run the color analyzer - doesn't that average out the color variation between the beans? Could be just me, but my eyes tend to interpret a more variable roast as being lighter.

The curves I've been showing are from Panama Elida Catuai natural processed beans. From what I've read, natural processed beans retain a coating of carbohydrates that make the beans more susceptible to burning than washed beans. I've also observed the darker I roast the more uniform the appearance - dunno why.

Once I drink down all the beans I've been running the experiments with, I'll run the same tests with some washed beans.

MNate wrote:it would be great to see RoR comparisons with the profiles Ikawa gives.

Do RoR curves make sense for the Ikawa? I get their purpose in the context of a drum roaster, which has significantly higher thermal mass than the beans. The Ikawa on the other hand, has negligible thermal 'mass', and the aggressive convective heat transfer in the Ikawa causes the beans to linearly track the applied temperature profile 1:1.

This is from one of my roasting runs:



Much of the RoR curve (blue) is largely flat, because the bean temp (green) is simply tracking the chamber temperature. I've read that the goal is a steadily declining RoR, which implies the beans are perpetually catching up with the chamber temperature - but I hit that milestone just two minutes in. I suppose I could tweak the Ikawa's temperature setpoints to mimic a drum roaster curve, but would that make the resulting roast taste better?