All coffee guides · Troubleshooting
A shot that takes more than 40 seconds for a 1:2 ratio is over-extracting — the water is moving too slowly through the puck and dissolving too many of the bitter, astringent compounds that appear in the later stages of extraction. Very slow shots can also stall completely or produce almost no flow at all. Both problems have a small number of causes that are straightforward to work through in order.
For a standard 18g in, 36g out double espresso, a shot time above 40 seconds indicates over-extraction. Between 35 and 40 seconds is borderline — worth tasting before adjusting, as some coffees and ratios work well at the higher end of the range. A shot that has no flow at all, or that barely drips, has a complete or near-complete blockage caused by grind, dose or tamping. A shot that starts slowly and then accelerates partway through may indicate that the puck is collapsing under pressure — a sign of overfilling. As with fast shots, taste alongside time: a slow shot that happens to taste balanced for a particular coffee may be correct despite the time.
Grind that is too fine is the most common cause of a slow shot. Very fine particles pack together tightly and leave minimal space for water to flow through. The fix is to grind coarser by one or two steps and pull another shot. One step coarser typically reduces shot time by two to six seconds depending on the grinder. If you have recently recalibrated the grinder, fitted new burrs, or switched to a denser coffee (such as a high-altitude washed coffee after a natural), the effective grind fineness may have increased without changing the setting. New burrs in particular grind finer than seasoned ones for the first few hundred grams.
Overdosing — using more coffee than the basket is designed for — creates a dense, over-compressed puck with high resistance. Most baskets are rated for a specific dose range: a 58mm VST 18g basket extracts best between 17.5 and 18.5g. Packing 20g into an 18g basket creates a puck that sits too close to the shower screen and compresses further when the portafilter is locked in, causing extremely slow or stalled flow. Weigh your dose consistently and match it to the basket rating. If you have been estimating by feel, check the actual weight — it is easy to drift above the target without noticing.
Excessive tamping pressure creates a very dense puck that resists water flow. The conventional guidance is that around 15-20kg of tamp pressure is sufficient to consolidate the grounds — anything above that adds resistance without improving evenness. In practice, the level of pressure matters less than consistency and levelness: a heavy, level tamp is better than a light, uneven one. If you have recently started tamping harder — perhaps after reading about technique — and shots have slowed down, ease the pressure slightly and check the time.
A basket with partially blocked perforations causes slow, uneven flow even when grind and dose are correct. Hold the clean basket up to a light source after washing: all holes should be clearly visible. If some are blocked, soak in a Cafiza solution for 20-30 minutes and scrub with a basket brush. A basket that consistently slows shots even after cleaning may be worn out — the perforations can become deformed and smaller over years of use, particularly with aggressive cleaning. Replacing the basket is the fix for a physically damaged one.
Lower brew temperature slows extraction and can contribute to a slow shot on machines where temperature affects flow rate. More commonly, a machine that is not fully warmed up produces lower temperature water that extracts differently and can cause inconsistent, slow shots. Allow at least 20-30 minutes for single-boiler machines to reach full thermal stability. Flush the grouphead with a blank shot — water only — immediately before pulling the first real shot to bring the grouphead and portafilter up to temperature. If the machine has been sitting unused for several hours, the thermal mass needs time to stabilise even if the boiler is at target temperature.
Browse all 98 coffee guides or start a free espresso journal on Baristalog.