Blistering on bean surface

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
starkiez
Posts: 3
Joined: 10 years ago

#1: Post by starkiez »







Hey all, could you please help me with a blistering problem?

I've tried lowering the drop temp as low as 70C on advice that it is the initial drum temp or charge, which makes sense. I've also tried a drop temp as high as 150C to speed the roast to a pretty standard 14 mins on advice that the roast was too slow. But whatever I do I still end up with blistering.

I've tried multiple profiles, almost every possible combination.

I've tried varying load weights, as low as 20g but no change.

I've gone through around 10kg trying to find a solution.

The flavour is sharp, rubbery. If I target 12% w/l, the origins flavour come through, but there's still an underlying rubbery mess.

The problem shows itself at first crack. I've read that perhaps the chaff has slowed the air flow, so tried increasing, but still no solution.

I've searched everywhere and can't find a solution.

This happens pretty randomly with many different beans, ranging in altitude from 900m - 2000m, but the high grown beans tend to get this result more often.

Maybe it's too much airflow at first crack? Where a portion of the bean cracks but suddenly cools?

I'm using a hottop with datalogger and 250g of green beans.

I target a weight loss of 14-15% but whenever this happens I almost always get around 13% loss.

I've tried extending the drying and coasting into FC, but no fix.

Hope you can help and thank you in advance,
Sam

Alan Frew
Posts: 659
Joined: 16 years ago

#2: Post by Alan Frew »

That doesn't look much like Arabica, and 12% weight loss seems very low. If those are Robusta beans, "rubbery" is to be expected, and I'd also suspect a higher than normal moisture content and low bean density as contributing to the blistering.

Alan

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starkiez (original poster)
Posts: 3
Joined: 10 years ago

#3: Post by starkiez (original poster) »

Thanks for your reply.

Your comment about moisture is interesting.

I'll try removing the filter on my hottop and extending the drying for as long as possible.

starkiez (original poster)
Posts: 3
Joined: 10 years ago

#4: Post by starkiez (original poster) »

Ok I removed the filter and got dramatically improved results, thank you!

I also did a weird thing by accident but still, it makes me think that the moisture level was far too high during first crack.