Rich, the part about turning fan to high for 30 seconds during drying is interesting to me. I've got two natural process coffees that have some excess bitterness no matter what I do. I too charge them around 300f (150c) and dry for 4.5-5 minute, but I generally keep the fan just high enough to maintain negative pressure. Both of these coffees have a lot of chaff and I'm wondering if some of that excess is burning and causing the bitterness I can't escape.

Up until now my experiments in trying to get rid of the bitterness have focused on raising airflow to control ET, but after my last couple of tests, I don't think that's the issue.

frank

boar_d_laze wrote:In an empty roaster, the BT probe gives you temperature at the location you care about. That's particularly true in roasters such as mine where the ET probe isn't even in the chamber-proper, but in the exhaust manifold. With a full roaster, real time BT/ET differential helps me predict RoR, and the ET plot provides a record of gas/air-flow manipulation.

Hey Rich
Thanks for your answers. I think it is important to remind myself that the ET / BT graphs depend largely on the placements of the probes.

dogjamboree wrote:Rich, the part about turning fan to high for 30 seconds during drying is interesting to me. I've got two natural process coffees that have some excess bitterness no matter what I do. I too charge them around 300f (150c) and dry for 4.5-5 minute, but I generally keep the fan just high enough to maintain negative pressure. Both of these coffees have a lot of chaff and I'm wondering if some of that excess is burning and causing the bitterness I can't escape.

Up until now my experiments in trying to get rid of the bitterness have focused on raising airflow to control ET, but after my last couple of tests, I don't think that's the issue.

frank

Frank, Is it possible to examine the chaff post-roast to see if it looks burned and does it have to be burned dark to impart the bitterness you mention?

Hey Laron,

Good question. I've looked at the chaff, and in some cases there will be some darker chaff, but nothing I'd describe as burnt. The particular natural process coffee I've most recently been working with has a lot of chaff present, so if there was a coffee where the chaff would be imparting a bitter taste, this would be the one.

I've looked at the chaff, and in some cases there will be some darker chaff, but nothing I'd describe as burnt.

I asked because with my roaster I clean the chaff tray after each roast and seldom see anything that looks burnt. My charge temps are very close to yours for Ethiopians - typically 315F to 320F for a 200gms load. I use a very low heat level and 40 volts to the fan to warm the roaster up to charge temp (typically takes about 10 to 15 min.) After charging, I recently found I could wait until a minute or so before DE at approx. 300F to increase gas flow to the burner. This still gets me to DE between 5min, 30sec and 6min. After FC, I drop between 412F and 420F after 1min, 30sec to 2min resulting in ML of 12.5% to 14.5%. As I recall, I've never had the bitterness you describe. Maybe it's just bad beans!