The Shot
Common shot symptoms
The espresso community uses a tight vocabulary to describe shots. Picking the wrong word sends a dial-in in the wrong direction, sometimes by a lot.
The under-extraction family
sour
Unpleasant acidity, mouth-puckering, citric or lemon-juice-like at the front. Almost always means under-extraction. Fix: grind finer, pull longer, raise temp.
bright / acidic
Pleasant high notes (lemon, berry, stone fruit, floral). Desirable, especially in light roasts. Do nottry to "fix" brightness or you'll kill the good part of the shot trying to remove it.
thin / watery
Low body, no syrupy mouthfeel. Either under-extraction or ratio too high.
muted
Flat, no clear flavour notes, lacks definition. Often stale beans, but also wrong ratio or under-extraction on darker roasts.
The over-extraction family
bitter
Harsh, dark-chocolate-or-burnt-on-the-tongue. Usually over-extraction, sometimes a stale or too-dark bean. Fix: grind coarser, pull shorter, drop temp.
astringent
Dry, puckering mouthfeel like strong black tea or unripe banana. A texture, not a taste. Caused by over-extraction or fines migration through the puck.
harsh
Aggressive, unpleasant. Often a combination of bitter, astringent, and heat.
ashy
Tastes like a wet ashtray. Roast too dark, water too hot, or shot pulled way too long. If the bean is past medium-dark and visibly oily, no dial-in fixes this. Try a different bag.
The channelling family
hollow
Thin in the middle, no sweetness, often acidic on the front and bitter on the back with nothing in between. Almost always channelling. Water finding a low-resistance path through the puck.
channelling
Visible signs are blonde streaks, side-jets, spritzing on a bottomless portafilter. Taste signs are sour AND bitter in the same shot, hollow, watery. Fix is puck prep (WDT, levelling, flat tamp). Do not tamp harder. That's not what channelling is about.
The roast-issue family
tobacco / smoky
Often a dark-roast tell or over-extraction on a medium-dark. Sometimes desirable in the cup, sometimes a sign you're past the bean's sweet zone.
papery / cardboard
Beans are oxidised. Past their roast date by enough that the volatile compounds have faded. Move on.
Why these distinctions matter
The knowledge base treats sour and bright as opposites. Picking the wrong one inverts the recommendation. A user typing "sour" for what's actually a desirable bright acidity in a light Ethiopian will be told to grind finer, which kills the high notes they liked. Same shot, called "bright", gets a different answer. Don't change anything, you're already where the bean wants to be.
When in doubt, taste a roaster's recommended brew (espresso bar, café, friend with good gear) for the same bean and calibrate your own vocabulary against it.