Definition
Flow dynamics describes how water travels through the coffee bed during brewing. Unlike immersion methods where all grounds contact water equally, pour-over is a percolation system where water must travel through layers of coffee.
The path water takes, the speed at which it flows, and whether flow is uniform or uneven all dramatically affect extraction and flavor.
Key Insight
In pour-over, not all coffee grounds extract equally. Some see lots of water contact (over-extracted), some see little (under-extracted). Managing flow creates extraction evenness.
Percolation vs Immersion
There are two fundamental brewing methods:
Immersion
French press, AeroPress, cupping
All grounds sit in water. Contact time is equal across all particles. Extraction is uniform but potentially incomplete since water becomes saturated.
Percolation
V60, Kalita, Chemex
Water flows through coffee bed. Fresh water constantly contacts grounds. More efficient extraction but risk of uneven flow and channeling.
Pour-over is percolation. Water enters at the top, percolates downward through the bed, and exits through the filter. Grounds at the top see different extraction conditions than grounds at the bottom.
Flow Resistance
The coffee bed acts as a filter. Water must push through small gaps between particles. This creates resistance, which slows flow and extends contact time.
Factors Affecting Resistance:
- •Grind size: Finer grounds create more resistance (slower flow)
- •Fines content: Tiny particles clog gaps, dramatically slowing flow
- •Bed depth: More coffee = longer path = more resistance
- •Roast level: Darker roasts are more porous and create less resistance
- •Water level: More water in the dripper = more pressure = faster flow
Ideal flow is neither too fast (under-extraction) nor too slow (over-extraction). A V60 brew typically drains in 2:30-3:30 total. Much faster or slower suggests a grind adjustment is needed.
Channeling
Channeling occurs when water finds a path of least resistance and flows preferentially through certain areas of the bed, leaving other areas dry or under-extracted.
Common Causes of Channeling
- •Uneven coffee bed (clumps, gaps, or tilted grounds)
- •Pouring too aggressively in one spot
- •Coffee bed cracking or forming a dry crust during bloom
- •Grind distribution with extreme fines creating barriers
When channeling happens, you simultaneously get over-extraction (in the channel) and under-extraction (in dry zones). The result is a cup that tastes both sour and bitter—confusing and unpleasant.
Preventing channeling: Level the bed before brewing. Pour in circular motions to distribute water evenly. Avoid pouring directly on the filter. Use gentle agitation (stirring or swirling) to eliminate dry pockets.
Brew Time and Flow Rate
Brew time is a proxy for flow rate. It tells you whether water is moving too quickly or too slowly through the bed.
Typical Brew Times (for ~20g coffee, 1:15-1:16 ratio):
- •V60: 2:30 - 3:30
- •Kalita Wave: 3:00 - 4:00
- •Chemex: 4:00 - 5:00 (thicker filter)
- •Clever Dripper: 2:00 steep + 1:30 drawdown
If your brew finishes in under 2 minutes, you're likely grinding too coarse—water is rushing through without extracting fully. If it takes over 5 minutes, you're grinding too fine—water is barely trickling and over-extracting.
Flow rate is a tool, not a rule. Some coffees (especially light roasts) benefit from slower flow and extended contact. But brew time gives you a reference point for consistency.