Percolation vs Immersion: How Brewers Differ

Two families

Percolation brewers pass fresh water through a bed of coffee: pour over, batch brewers, espresso, moka pot. Each gram of coffee keeps meeting new, less-saturated water, so the concentration gradient stays steep and extraction can go high¹. The trade-off is unevenness — water finds the path of least resistance, and channelling is the enemy².

Immersion brewers hold all the water and all the coffee together: French press, AeroPress (mostly), cupping bowls, cold brew, siphon. Extraction is extremely even — every particle sees the same water for the same time — but the water saturates as it goes, so the ceiling is lower¹. Immersion brews usually land 1–2 % EY below the same coffee as a pour over, a practitioner observation², and taste rounder and heavier because more fines and oils reach the cup.

The table is Cup Engineering's summary of the mechanism above and of practitioner experience²³.

Pour over (V60, Kalita, Chemex, Origami)

Paper-filtered percolation. Cones (V60) drain fast and reward technique; flat-bottom brewers (Kalita Wave) keep a flat bed and are more forgiving. Chemex uses a thick filter that slows flow and strips oils for a very clean cup².

Key levers: pour schedule, agitation, bed flatness, water temperature. Typical: 1:16, medium grind, 93–96 °C, 2:30–4:00, which are Cup Engineering's calculator defaults and common practice³.

Batch / drip machines

Same physics as pour over, without the hands. The good ones (SCA-certified) hold 93 ± 3 °C at the shower head and pulse the water⁴; the bad ones run cold and dump it all at once. A pre-wetting pause and a flat bed matter as much here as in a manual pour over.

Espresso

Percolation under pressure through a compacted bed of very fine coffee. Nine bar is the traditional figure⁵: pressure forces water through a bed that would otherwise not drain at all, and the fine grind gives huge surface area — extraction happens in under 30 seconds. Crema is CO₂ and emulsified oils forced out under pressure⁵.

Two recent studies qualify the "9 bar" rule. A 2020 modelling-and-experiment study found that reproducible, high-yield shots came from coarser grinds and lower doses than tradition suggests, because very fine, tightly packed pucks channel⁶. And a 2026 study that instrumented a café machine found that above roughly 5 bar, pushing harder no longer increased flow: the puck compacts under the load, so the extra pressure is spent squeezing the bed rather than moving water through it⁷. Neither says 9 bar is wrong; both say it is not a magic number, and that grind and puck preparation matter more.

Pre-infusion, pauses and pressure profiles are covered in Blooms, pulse pours and pre-infusion.

Because the bed is so fine, espresso is uniquely sensitive to puck preparation: distribution, tamping, and headspace. Channelling — water blasting through one weak spot — is the dominant failure mode and produces sour and bitter in the same cup⁶.

Moka pot

Steam pressure pushes hot water up through a bed of fine coffee. The pressure involved is far below espresso's (on the order of 1–2 bar, a figure from practitioner descriptions rather than a measurement in our sources³). Not espresso, despite the marketing: the water is often too hot (it's boiling by the time it reaches the coffee), which is why low heat and starting with pre-heated water matter so much. Cup Engineering's model targets 2.5–4.5 % TDS for moka, a working parameter chosen from practice, not a standard.

French press

Pure immersion with a metal mesh. Everything ends up in the cup — oils, fines, silt — which makes for heavy body and a muddled finish. Long steeps with a coarse grind, then decanting without plunging, gives a far cleaner result³.

AeroPress

Hybrid: an immersion steep followed by a short pressurised push through a paper filter. Fast, clean, and tolerant of almost any parameters, which is why it has produced the widest range of recipes of any brewer. Works from 80 °C to boiling, 1:6 concentrate to 1:17 straight, 30 s to 6 min; those ranges summarise published recipes rather than any standard³.

Cold brew

Long immersion at room or fridge temperature. Extraction is slow at 20 °C because both solubility and diffusion fall with temperature¹. The usual description — smooth, sweet, chocolatey, less aromatic — is widely reported and consistent with slower extraction of the heavier, more bitter compounds, but that mechanism is Cup Engineering's working assumption; our sensory sources cover hot drip coffee only.

Siphon / vacuum

Immersion at a very stable, high temperature with vigorous convection, then a vacuum draws the coffee through a cloth or paper filter. Clean, bright, theatrical.

Choosing

If you want to understand a coffee, cup it or brew immersion — the evenness is diagnostic. If you want the most a coffee can give, learn a percolation method and put the time into technique. The recipe library lets you filter by method and see which coffees each recipe author had in mind.

How the numbers are computed

The calculator carries one set of parameters per method (METHODS in lib/coffee.ts): a base extraction at default settings, the grind at which that base holds, default temperature, contact time and ratio, water retained by the spent grounds, and a target strength window. For example pour over is 20 % EY at grind 6, 94 °C, 180 s, 1:16.7, retaining 2.1 g of water per gram of coffee, with a 1.15–1.45 % TDS target; espresso is 20 % at grind 1.5, 93 °C, 28 s, 1:2, retaining 1.1 g/g, targeting 8–12 %. These are Cup Engineering working parameters that encode typical practice³²; only the 18–22 % extraction range and the filter strength window trace to a standard⁴. Every prediction on the calculator page is those parameters plus the four lever terms described in the extraction article.