Before bottomless portafilters became popular, most baristas used spouted portafilters for espresso extraction. These came in two main types — single-spout portafilters for single shots, and double-spout (split-flow) portafilters for double shots.
The double-spout design was ingenious: it divides the espresso evenly into two streams, allowing baristas to pull two single shots at once — perfect for café service and combo orders.
However, many of us have encountered a frustrating issue:
One spout flows beautifully, while the other barely drips… or doesn’t flow at all. This imbalance doesn’t just look off—it directly affects flavor, aroma, and consistency.
So why does espresso sometimes flow unevenly from the two spouts? Let’s break it down.
What Does “Uneven Extraction” Mean?
Uneven extraction happens when water doesn’t flow evenly through the coffee puck during brewing. Ideally, espresso should flow symmetrically from both spouts, forming a smooth, golden stream.
However, if one side extracts faster, the result is often:
- One over-extracted (bitter) side
- One under-extracted (sour or weak) side
The final cup ends up imbalanced in taste—lacking sweetness, clarity, and body.
Main Causes of Uneven Espresso Extraction
1. The Simple but Overlooked Reason — The Machine Isn’t Level
It might surprise you, but one of the most common causes of uneven espresso flow has nothing to do with your puck prep — it’s the level of your espresso machine.
If your espresso machine (or the countertop it sits on) is slightly tilted to one side, gravity will naturally pull the espresso toward the lower side.
When that happens, one spout will flow faster and more heavily than the other.
Common causes:
- The espresso machine was never perfectly leveled.
- The countertop has sagged or warped slightly over time from the machine’s weight.
How to fix it:
- Use a bubble level or a smartphone leveling app to check your machine’s alignment.
- Adjust the machine’s feet or place thin shims under one side until perfectly level.
It’s a quick and simple adjustment that can instantly restore even espresso flow!
2. Channeling — The Main Culprit Behind Uneven Extraction
If your espresso machine is level but you’re still seeing uneven flow, the next likely cause is channeling inside the coffee puck.
In a perfect extraction, hot water passes evenly through the coffee bed, gathers in the center, and flows smoothly into the spout.
But when channeling occurs, water finds weak spots or cracks in the puck, shooting through some areas faster than others.
The result: the coffee doesn’t form a centered liquid column — instead, it exits from one side, causing uneven split flow.
Why does channeling happen?
- Uneven coffee distribution — grounds are denser on one side.
- Uneven tamping pressure — the puck surface isn’t level.
- Clumps or static — creating dense and loose areas in the puck.
3. The Role of Static and Clumping in Uneven Extraction
Static electricity may sound trivial, but it significantly affects espresso uniformity. When static builds up during grinding, it causes coffee clumps that make the coffee bed uneven in density.
This is why many modern grinders — like the Geimori GU64 — feature Plasma Anti-Static Technology to eliminate static and prevent clumping.
With more even grounds, water resistance remains consistent throughout the puck, leading to a smoother, balanced espresso extraction.
- Pro tips to reduce static and channeling:
- Use a fine mist of water (RDT technique) before grinding.
- Distribute grounds evenly with a WDT tool.
- Tamp level and consistently, avoiding over-compression.
- Keep your grinder and portafilter clean and dry.
Final Thoughts
Uneven espresso flow isn’t just a visual issue — it’s a sign of uneven extraction, which can lead to unbalanced flavors.
The good news? It’s almost always fixable with a bit of attention and the right tools.
By ensuring your espresso machine is level, improving puck preparation, and using a consistent, low-static grinder like the Geimori Series, you can achieve beautifully symmetrical espresso flow — and more importantly, a perfectly balanced cup.
