[Demarche]

So, I'm relatively new to the Audio Circle. I've made a few posts and found some very interesting posts. One in particular has been about home coffee roasting. After reading the info that everyone here has provided (thanks! ) and cruising the web and the local library I decided to give it a try.
I got a hold of a couple hot air poppers (Popcorn Pumper) and I've had some limited success. One thing I have struggled with is getting the beans to the "oily" stage.
Well, I was able to do that tonight right as pumper #1 died  . Not too much of a problem because I have a back up, which I have used a few times and works.
One thing I keep seeing is on the rounded side of the bean a small round piece of the outer shell breaks (or flakes) off revealing the interior of the bean and it appears burnt. Here is a slightly out of focus photo but I think it still gets the point across. I have seen this on most of my roasts. It seems to coincide with the 2nd crack. My question to the coffee roasting gurus is, is this typical? Can you explain what is happening at this stage?

Thanks in advance.

[mikef]

Here's a link to Sweet Maria's guide to home roasting with an air popper:
http://www.sweetmarias.com/airpopmethod.html

Great information on this website.

Mike Fox

[loki1957]

The flakes coming off is called chaff. Some beans produce more of it than others. It is normal. If your beans are burning as your picture shows put less beans in the roast chamber. The air flow isn't moving the beans enough. I like my roast to be stopped just as I hear the 2nd crack starts. I don't like dark roasts. For some reason all coffee shops have tried to tell people this the way coffee should be done. Too bitter for me. It takes some time to learn when to stop the roast. Also a cool down is very important. The beans will continue roasting if they don't cool fast enough. Keep trying, you'll figure it out.

[Demarche]

MikeF - yes, I've been using the info from the sweetmaria's website. it is a great resource.  I purchased the green beans from them as well.

loki1957 - I don't think this is the chaff. I am seeing the chaff come off at the start and mostly through to the 1st crack.
The issue I seem to be having is a small circle portion of the outer shell is breaking off at or around the 2nd crack. The amount of bean doesn't seem to affect this. I have seen it while roasting 1 oz, 1.5 oz, 2 oz, 2.5 oz, & 3 oz. It wasn't until I increased the batch size to 2.5 & 3 oz that I was able to start to see the oily sheen that is associated with the darker roasts. I am trying to get a very dark roast, as I am an espresso drinker.

On a side note pumper #1 is back in service. It appears to have over heated and did not burn out.

[mikef]

Demarche - I think that you're correct - what you're seeing is the physical effect of second crack - a little crater as the bean literally explodes. I've seen it in my own roasts when I've roasted too far into 2nd crack. According to Sweet Marias website:

"First crack is the physical expansion of the coffee seed as water and carbon dioxide split and CO-2 outgassing occurs. Second Crack is the physical fracturing of the cellular matrix of the coffee."

Cooldown is very important when you hit the right roast level you require. Sounds like you want a French Roast, but once the bean gets there, unless it's rapidly cooled it will continue to roast, sometimes until it's burned. I'm not sure how to rapidly cool down a hot air popper. When I started home roasting I bought a Fresh Roast +8 that gave me control over the heating element, and I learned to think 20-30 seconds ahead of time, knowing that when I hit 2nd crack and turned off the heating element to allow cooler air into the chamber, the beans would continue to roast for that amount of time. Mine was $80 with 8 lbs of coffee, but I see they've raised the price.

You probably have seen this chart, but an explanation of the various stages of roasting with pictures is available here:
http://www.sweetmarias.com/roasting-VisualGuideV2.html

Mike Fox

[bummrush]

 Cant really tell from pic.But are you far into 2nd crack,i get a few of those from time to time but not many.I think the official word for em is divits but not sure

[BobM]

I always used one of those roasters that also has a cool down cycle. It literally keeps blowing the beans about without heat to cool them to semi-room temperature. I think you could try sifting the beans from one plate to another, keeping one about a foot or so above the other and letting the chaff blow off (I would do this outside). It's not elegant, but it will probably work to cool them much more than just letting them sit there.

You still need to keep the beans airing out for the next 2 days or so before grinding. This lets other gasses blow off that could otherwise ruin your brew.

I'vve found some beans really like a dark roast, and others like it lighter. It's trial and error with each one until you find what you like. Me, I liked Guatemala beans just past 2nd crack.

Enjoy,
Bob

[loki1957]

There is instructions somewhere on the web that explains how to install a toggle switch to turn the heat element off so just the blower runs. I had one of these an engineer friend gave me. I gave it away when I found a good price on a Sonnofresco.

I recommend trying some different roasts for your espresso. I roast mine to where the beans just start to show oil.

[Demarche]

Thanks All! This helps a lot.

I'm not sure I would have figured out that "Second Crack is the physical fracturing of the cellular matrix of the coffee" equated to the appearance of the divit.

Adding the toggle switch to the heater element shouldn't be a big deal. Right now I dump them into a collinder and run water over them in the sink.

I am surprised to hear that the beans continue to off-gas for 2 days, not that I've been grinding them immediately, that just seems like a long time after they've cooled.

[loki1957]

You will find also that Espresso roasts will taste better after sitting a few days. Not so much so with drip coffee. It took me a while to be able to determine 2nd crack. I would always under roast till I got the hang of it.