Dialing In a New Single Origin
You are working a busy Saturday morning shift at a specialty café. A new single-origin Ethiopian coffee has just been roasted and rested for 7 days. The barista before you dialed in the espresso machine using the same recipe as the previous blend: 18g in, 36g out, 25 seconds. However, the shots are pulling very fast (18-20 seconds) and taste sour and thin. The grinder is a Mazzer Major with flat burrs that were replaced 3 months ago. The espresso machine is a La Marzocco Linea PB with dual boilers, and the brew temperature is set to 93°C. The coffee is stored in a sealed bag with a one-way valve, opened this morning. The café uses a scale with 0.1g resolution and a timer. The barista is using a bottomless portafilter and a distribution tool. The dose is consistent at 18.0g ±0.1g. The beans are a light roast with visible chaff. The grinder setting is at 2.5 on a scale from 1 (finest) to 10 (coarsest).
1. What is the most likely cause of the fast, sour shots, and what adjustments would you make to the grind setting and other variables to improve the extraction?
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The fast shots (18-20s) and sour taste indicate under-extraction. Given the light roast and 7-day rest, the beans are likely dense and require a finer grind. The previous blend probably needed a coarser setting. The grinder is at 2.5, which may be too coarse for this coffee. I would first adjust the grind finer in small increments (e.g., to 2.0) and keep dose and yield constant. If the shot still runs fast, continue finer. Also, check that the temperature is appropriate for light roast (93°C is reasonable, but some light roasts benefit from 94-95°C). Ensure even distribution and tamp. If channeling is suspected, improve distribution. The goal is to extend shot time to 25-30s and increase extraction to balance sourness. Taste and adjust.
2. After adjusting the grind to 2.0, the shot time increases to 22 seconds but still tastes sour. What could be the next step? Consider other variables that might affect extraction.
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Even at 22s, the shot may still be under-extracted. I would continue grinding finer (e.g., to 1.8) to extend time to 25-30s. However, if the grind is already quite fine, other factors could contribute: 1) Dose: increasing dose to 18.5g or 19g might increase resistance and extend time, but also changes ratio. 2) Temperature: increase to 94°C to enhance extraction of light roast. 3) Yield: reducing yield to 34g might concentrate the shot and increase extraction percentage. 4) Distribution: ensure no channeling, which can cause sourness. 5) Water quality: check TDS and alkalinity; if water is too soft, extraction may be low. 6) Bean freshness: 7 days rest is good, but if beans are very fresh, they may degas and cause uneven extraction. I would prioritize grind and temperature, then evaluate.