My daughter and her husband are in for a visit. They were in Kenya for a while and brought me some bags of Kenya AA from there. One of the bags has a few "roasted" kernels of corn among the nicely medium roasted beans. We have come to the conclusion whoever roasted these beans used corn kernels to end the roast when they "popped". They must have missed a few unpopped kernels before bagging. Anyone heard of this type of roasting?

In my role as a wetware version of "AI" search engines, you made me look it up:

Corn starts popping way below first-crack temperatures (180C) - unless these were specially engineered popcorn kernels. Nonetheless, the slightly higher moisture content and rapid application of heat could delay the actual popping to allow enough heat into the coffee greens to carry them through. Perhaps one of the workers at the farm packed a corn cob for lunch? Corn is the second biggest crop grown in Kenya...

Still like the idea though: "pseudo greens" engineered to pop or change color when prescribed temperature levels are reached. Bluetooth with a phone app would be nice.

So, if you find a popped corn kernel in your roasted coffee, do you leave it in when you grind it, for the additional flavor notes?

Corn pops too early for ending a roast (except maybe for pre first crack tea-style coffee as used by some Ethiopians). But in a large drum roaster, it'll pop just about at the temperature when you want to cut off the heat and let it coast in. If you have a roaster with no thermometry at all, a few kernels may be just the ticket for getting a nice smooth roast finish.

Is this a potential hack for small-batch air roasters? First crack is difficult to discern above the fan noise when the charge size is less than 100g. Side benefit: the airflow will drive the kernel to auto-eject once it pops. Guessing someone already asked this years ago...

It's not uncommon to find corn accidentally mixed in with green coffee. Like sticks and stones. My guess would be that it was dried or somehow handled where corn had been. Regular corn kernels (not popcorn) won't pop and are sometimes roasted at about the same temperature as a medium roast - to be eaten as hard, crunchy snacks.

Jonk wrote:It's not uncommon to find corn accidentally mixed in with green coffee. ...

That makes good sense; except it's not what one would expect from Kenya AA, which is a high end prep, supposedly hand sorted. I guess even the sorters can have a bad day.

I've only heard of corn kernels winding up in Ethiopian coffees, never high end Kenyan AA, so this is interesting to me.

Ethiopian's consume a massive amount of popcorn and it's not uncommon to accompany coffee.

another_jim wrote:That makes good sense; except it's not what one would expect from Kenya AA, which is a high end prep, supposedly hand sorted. I guess even the sorters can have a bad day.

My thoughts too. The kernels were much smaller than the AA beans, but they did take on that nice medium brown color. It's a 375g bag, used about 2/3 of it and out of that just 3 kernels so far (that I found).

Didn't leave them in to be ground with the beans for fear the kernels might damage my burrs.

Just for fun... here's what happens when there's too much corn and not enough coffee in your roast chamber.