Coffee: Pour-Over Brewing — Ratio, Temperature, and Bloom

Pour-over is a percolation method: water passes through a bed of coffee grounds once, extracting as it drains through a filter. Unlike immersion methods (French press, AeroPress, cold brew), percolation means fresh water is always contacting the grounds — which generally produces a cleaner, brighter cup with lower TDS than equivalent immersion brews.

Core Parameters

Parameter	SCA Target	Typical Range
Water temperature	93°C	88–96°C depending on roast
Brew ratio	1:15–1:17	1:14 (strong) to 1:18 (light)
Bloom water	2× coffee weight	e.g., 30g water for 15g coffee
Bloom time	30 seconds	25–45 seconds for very fresh coffee
Total brew time	3–4 minutes	Varies by device and grind
Grind size	400–700 microns	Medium-fine to medium
TDS (in cup)	1.2–1.45%	SCA brewing control chart target

The Bloom

The bloom is the initial pour of water — typically twice the weight of coffee (e.g., 30g water for a 15g dose) — that saturates the grounds and is allowed to rest for 30 seconds before the main brew pours begin.

Fresh-roasted coffee contains CO₂ trapped in the cell structure of the beans, a byproduct of roasting. When hot water contacts the grounds, CO₂ off-gasses rapidly, visibly causing the coffee bed to puff and bubble. If extraction begins immediately over this agitated bed, CO₂ creates a barrier between water and coffee particles, reducing extraction efficiency and causing uneven contact time across the bed.

The bloom allows this initial gas release to complete so that subsequent pours contact coffee grounds evenly. Coffee roasted more than 4 weeks prior may produce minimal bloom, signaling lower freshness.

Pour Technique

Most specialty pour-over recipes use a center pour approach:

1. Begin in the center of the bed and pour in a slow, controlled spiral outward to the edges.
2. Avoid pouring onto the filter walls, which bypasses the coffee bed entirely.
3. Maintain a consistent pour height (5–10 cm above the bed) for controlled agitation.
4. Multiple smaller pours (pulse pouring) vs. a single continuous pour both work — pulse pouring allows the bed to drain slightly between additions, potentially increasing extraction.

The goal is to keep the coffee bed evenly saturated and moving, without overflowing the dripper or creating channels where water bypasses grounds.

Device Comparison

Device	Filter type	Bed shape	Drainage	Ease of use	Flavor character
Hario V60	Paper (or metal)	Conical, single large hole	Fast, variable	Moderate	Bright, clean, complex
Chemex	Proprietary thick paper	Conical, pinched waist	Slow-medium	Easy	Very clean, light-bodied, clarity-focused
Kalita Wave	Paper (flat-bottom wavy)	Flat, three small holes	Slow, controlled	Forgiving	Full-bodied, even extraction
Origami	Paper (conical or flat)	Conical or flat, interchangeable	Variable	Moderate	Versatile, dripper-dependent
Melitta	Paper (single hole)	Wedge	Very slow	Easy	Full extraction, slightly heavier

The Chemex’s thick bonded filter removes significantly more oils than standard pour-over paper filters — roughly 20–30% more lipid content is absorbed by the filter itself. This results in measurably lower TDS and a lighter-bodied cup that prioritizes flavor clarity and brightness over richness.

Temperature and Roast Level

Water temperature interacts with roast level:

Roast level	Recommended temp	Reason
Light roast	93–96°C	Higher density requires more thermal energy; preserves bright acids
Medium roast	91–93°C	Balanced extraction at moderate temperature
Dark roast	88–91°C	Cells are more porous; high temp accelerates bitter extraction

Dark roasts have undergone greater cell wall degradation and extract much more readily. Lower temperatures slow the extraction of harsh, bitter compounds that are more prominent in dark-roasted coffee.

Brew Ratio and Strength

Pour-over brew ratio directly controls the concentration (TDS) of the final beverage:

Ratio	Coffee (g) for 250ml	Character
1:14	18g	Intense, very strong
1:15	17g	Strong, full-bodied
1:16	15.6g	Balanced, SCA lower target
1:17	14.7g	Light-medium, SCA upper target
1:18	13.9g	Light, delicate

Grind size and pour technique determine extraction yield (how much of the coffee’s mass is dissolved) independently of ratio. A correct ratio but poor extraction technique can still produce a weak or hollow cup. The SCA Brewing Control Chart plots TDS against extraction yield to define an “ideal” zone of 1.2–1.45% TDS at 18–22% extraction yield.