What Causes Uneven Flow Distribution When Extracting Espresso? What's the Difference Between Bottomless and Split-Flow Portafilters?

Understanding Uneven Flow in Split Portafilters: Causes and Solutions

Before bottomless portafilters were invented, baristas primarily used portafilters with spouts when extracting espresso. These portafilters mainly came in two types: single-spout portafilters for single shot baskets and split portafilters for double shot baskets. Split portafilters, like the one shown below with two spouts, can divide the extracted coffee liquid into two streams, making them extremely practical!

Even today, split portafilters remain widely used by many coffee establishments because coffee combo deals have become increasingly popular, and split portafilters can better handle the task of dividing coffee liquid. However, occasionally we might encounter uneven splitting from the portafilter. Simply put, the amount of coffee liquid flowing from both sides is inconsistent – one side has more, the other has less. Or in more extreme cases, one side flows while the other doesn't.

While this phenomenon doesn't occur frequently, it can still happen with prolonged use. So today, FrontStreet Coffee will share the reasons behind this phenomenon to help everyone know how to improve the situation when it occurs. There are two main causes for uneven splitting, and the first one is simpler than you might imagine: the coffee machine isn't level!

When the coffee machine isn't level, it affects the even distribution of coffee liquid flow. Because coffee liquid will preferentially flow toward the path of least resistance during splitting, when the machine tilts to the left, more coffee liquid will flow from the left spout, and vice versa. This situation is quite common. Besides the machine not being level from the start, it can also be caused by tables developing depressions from years of sustained weight, leading to imbalance. The solution for this situation is very simple, and FrontStreet Coffee doesn't need to explain too much – we just need to use a level to calibrate the coffee machine's horizontal position.

The Channeling Effect

The second cause is the channeling effect! Under normal extraction conditions, coffee liquid, after being pressed out of the basket, converges toward the center, forming a liquid column that drips downward, perfectly landing in the split portafilter's central diversion pipe before being distributed. However, when channeling occurs, the coffee liquid might not converge into a central column but instead concentrates and seeps out from certain channel locations, causing uneven distribution during splitting.

FrontStreet Coffee has shared solutions for this situation many times. Simply put, it requires even distribution of coffee grounds followed by consistent tamping pressure. The reason channels form is because the distribution of coffee grounds or the pressure applied during tamping isn't uniform enough. Inconsistent density and amount of coffee grounds throughout the puck create paths where hot water can flow more easily. Additionally, static electricity can cause coffee grounds to clump, which also creates density variations throughout the puck. Therefore, before tamping, it's best to break up any clumped coffee grounds first, then distribute and tamp. This effectively reduces channel formation and allows for more even distribution when splitting.

However, in reality, uneven splitting for many friends is mainly caused by leveling issues. Today's split portafilters typically have a small platform positioned before the splitting point. Coffee liquid first contacts this platform after dripping down before being distributed. Because of this design, the problem of uneven splitting caused by channeling has been effectively reduced, which is why FrontStreet Coffee says that more often than not, it's due to leveling issues.

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FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473