Light roasts usually need tighter process control. A reliable starter profile is 1:2.3 to 1:2.8 at about 93 to 96C, with grind and dose consistency treated as non-negotiable.
Set a light-roast starter profile
Start with one dose, target ratio 1:2.3 to 1:2.8, and aim for 25 to 35 seconds on a classic flow profile.
Use temperature between 93C and 96C based on your machine and coffee style, then hold it steady while setting grind.
Use threshold-based grind decisions first
If time is 18 seconds or faster, move 2 to 3 micro-steps finer before touching temperature. If time is 19 to 24 seconds, move 1 micro-step finer.
If time is 36 seconds or slower, move 1 to 2 micro-steps coarser first. If time is 45 seconds or slower, use a larger coarse correction before changing ratio.
Tune ratio and temperature after flow is stable
After time lands in 25 to 35 seconds, adjust ratio in 1 to 2g yield moves. Then change temperature by 1C steps only if taste still trends sour or bitter.
If a shot remains sour after grind and ratio are in range, raise temperature 1C. If it becomes dry and ashy, lower temperature 1C and retest.