I've noticed that my home roasted beans tend to create more channeling espresso shots than ones from a professional roaster. I'm usually roasting South American coffees from Sweet Maria's that are denoted "good for espresso". I look for ones that recommend full city / full city + and roast them on my Fresh Roast just until I hear 2nd crack starting. Then I throw them straight into a metal mesh with a fan blowing through it to cool the beans off fast.

I don't have any extra thermometry on my roaster besides the heating element temperature. I usually get the heat up to 9 (full power) until I get into a rapid 1st crack, then back off to 8 or 7 to try to extend the roast period. I wonder if I am baking the beans, and if this would create more channeling shots. Next roasting session I will try to not back off the heat at all, but I'd love to get some advice here. Thanks!

Try lowering the temp on the espresso machine. There is some discussion of it in this video near the end during Q&A. Basically if you are roasting nearly into second crack. My stronger suggestion is try dropping earlier and see if you like the espresso. My wife and I much prefer our espresso that way after becoming home roasters.

Hi Michael,

Thank you for the suggestions. I do use relatively low brew temperatures (196 - 198 F). When you say "dropping earlier", does that mean to roast for less time?

Yes, give it a try. Going nearly to second crack means you are tasting roast flavors and not origin flavors. In addition, you are heating some of the oils out that will cause more channeling.

Not saying you will like it better, just saying experiment. When my wife the pastry chef and I did it, we loved the flavors.

I had never heard that roasting darker causes channeling. Usually my beans show just a little bit of oil on the surface (in small patches, not covering the bean), or no visible oil at all. I've never had a problem with beans bought from a roaster that look like this, and I know some use bags of Lavazza that look much darker.

Darker roasts are less dense and more porous. Listen to the video at 26:50 on. Less dense and more porous, means more heat breaks the grinds down faster, maybe causing channeling.

Rest your beans for a week. Too much CO2 causes channeling.

Simple - but a good reminder. Since I've returned to home roasting, sometimes I do not manage my roasted supply as well as I'd like. I think the beans I was using yesterday had rested 5 days, I should try to get in a cycle where they are around 10 days before I use them.

The beans are ~13 days old now, and I have also reduced my dose from 18 to 17g. They are behaving much better now! I think resting them longer was probably the key.

I did go lighter on my most recent roasts, but I'll have to let those rest for a while before I try them

I started brewing my lighter roasted beans today. They are still ~30 seconds after all of the slowly fading 1st cracking has ended.

I pulled it at 18 in : 45 out with moderate preheating on the Robot. The taste was actually nice, just a little watered down for my liking. Still, I liked it more than my recent order from Onyx. I find I have to pull at a longer ratio to get rid of the sourness. I will try to grind a little finer, but I can only go so fine on the Robot before it becomes a workout.

When I roast into 2nd crack, I can usually pull it at 18 in : 30 out and get a very thick, rich shot.

I am now scheduling my roasting better so I can allow for about 7-10 days rest before I break into the batch.