I'm thinking perhaps it'll be better for some milk blends to be roasted darker than this but I'm finding anything I do that goes much darker or anywhere near 2Nd crack turns out super oily and very metallic/carbony/ashy/dirty in the cup.
Given the roasters you own, I'm probably not in your league, but here's my take on it. First, a few questions
- Which roaster, your Has or your Bella or both? If it is only one roaster then you've got a clue about whether it is machine related.
- What coffee bean, or is it several? Again, here we can perhaps narrow it down and see if it is related to a particular bean or maybe a bad batch.
Now for some uninformed
- John is definitely onto something concerning the oil. At the stated degree of roast there should be no immediate oil. Immediate oil only occurs with extremely dark roasts (Eventual oil is a sign of old roasted beans). This makes me wonder how you are judging the degree of roast. Most of us with tiny roasters go by the sound. But, with experience, and with big roasters and automated roasters, eventually we go by the temperature. (Even with my little Quest M3 I'm increasingly looking at the temperature and listening less than I did when I was getting used to it.) If you're going by sound, then 2C is 2C. But, if you're going by temperature then perhaps your setup has a malfunction and is reading too low. Thus, your degree of roast is much darker than anticipated, leading to the appearance of immediate oil. This might also bear on Jim's comment about too high an ET. Your ET may be higher than what's being displayed on your readout.
- Carbony/ashy could be due to the same thing. With the degree of oil I imagine you are describing you may be getting close to a Spanish roast. I've only once gone there in all the roasting I've done, but those two words definitely describe the horrible taste in the cup (only time I've ever had to bin a batch). However, that may not be the only factor. Lack of air flow can impart a burnt flavour in darker roasts. When I go to Italian or French (rarely these days), I keep the air flow on high (Quests have crummy air flow) or my wife will complain that I've burnt the batch. Metallic taste, on the other hand, I have no idea about. I've never let my roasters get hot enough to know, but I wonder if a really hot roaster would impart a metallic taste; certainly, one can smell hot metal...perhaps one can taste it too.
- I also wonder about your cooling regime. If you are used to light roasts, then cooling may not show up as a problem if the cooling is too late or too slow...one would simply have a somewhat darker roast than anticipated. However, if you are, knowingly or unknowingly, flirting with something really dark, then slow or delayed cooling might allow the roast to coast into something Spanish (my apologies to the Latinos here...I didn't invent the term
That's all I can think of.