I recently roasted a blend that was 70 percent high acidity columbian and 20 percent pulped natural Brazil. Both coffees tasted balanced on the cupping table. The Columbian was roasted with a 3 minute Roast development time to bring down the acidity. As an espresso with milk it was coming out with sour notes. Should I roast it darker or should I just adjust the blend? It feels like I roasted both coffees to the best of their ability. Or is this a barista brewing problem?
adjust the blend. I would lean more to 65/35 in favor of the Brazil.
It really depends on how specific flavors present themselves at various roast levels.
IF you are doing the roasting for clients, it's up to you to know how their machine is setup and if/how willing they are to adjust the machine. It's your responsibility as the roaster to know the suggested shot parameters for any and all coffees you are selling to be pulled as shots.
We pull EVERY coffee we roast as espresso at our coffeehouses. To be sure not all are pulled with the same shot dose weight, temp, time or extracted weight (more accurate than volume). Just last night at a going away party for a key employee leaving for a SE Asia sabbatical I was pulling shots of private stash light roasted Guatemala Gesha.
That said IF you are roasting for generic espresso setups across the board ~18g dose ~200f temp ~25sec pull ~32g yield etc. it's up to you to adjust your roast and blends accordingly. CUPPING results are not directly relevant to shots.