Kalita Wave 185 vs 155: The Flat Filter Changes Everything

You bought the Kalita Wave 185 because everyone said it was the dripper for beginners. You followed the recipe, dialed in your grind, and pulled a cup that tasted flat, thin, and strangely hollow. Then you saw the 155, the smaller sibling with the exact same flat bottom, and you wondered if the smaller size was just a marketing gimmick or if it actually changes the physics of your brew. The answer is not about capacity. It is about the geometry of the filter paper, the surface area of the coffee bed, and how those two variables interact to control extraction yield.

Choosing between the Kalita Wave 185 and 155 is not about how many cups you need to make for your morning routine. It is about matching the physical geometry of the dripper to the chemical structure of the bean you are brewing. The 185 and 155 are not simply scaled versions of each other. They are two distinct extraction instruments that demand different grind sizes, different water distribution patterns, and different expectations for the final cup.

The Geometry of the Flat Bottom

The defining feature of the Kalita Wave is the flat bottom with three small drainage holes. This design creates a perfectly flat coffee bed, which sounds ideal on paper but creates a specific extraction challenge. Because the bed is flat, the water must travel through the entire layer of coffee grounds to exit. This creates a longer contact time and a more uniform extraction profile than the V60, where water channels down the spiral ribs and exits faster.

The difference between the 185 and 155 lies in the diameter of that flat bed. The 185 holds a larger volume of coffee, typically 15 to 20 grams, creating a wider, shallower bed. The 155 holds 7 to 12 grams, creating a narrower, deeper bed. This difference in diameter changes the ratio of the filter paper’s surface area to the coffee mass. In the 155, the paper wraps higher up the sides relative to the amount of coffee, creating a larger surface area for the water to contact before it reaches the exit holes. This subtle geometric shift changes how the water moves through the grounds.

When you brew in the 185, the wider bed allows water to pool slightly in the center before finding its way to the edges and draining. This central pooling increases the immersion time for the center of the bed, which is often the hardest part to extract evenly. The 155, with its narrower diameter, forces the water to travel a shorter horizontal distance before hitting the paper walls and draining. This makes the 155 inherently faster and more responsive to your pour technique. If you pour too aggressively, the 155 will drain quickly, leading to under-extraction. If you pour too slowly, the 185 will hold the water longer, risking over-extraction of the finer particles.

Matching Bean Structure to Dripper Geometry

Not all coffee beans behave the same way in a flat-bottomed dripper. The structure of the bean, determined by its altitude, processing method, and varietal, dictates how easily water can pass through the grounds. High-altitude beans, like those from Ethiopia or Kenya, are dense and hard. They resist extraction. Lower-altitude beans, like many Brazilian or Sumatran coffees, are softer and more porous, allowing water to pass through more easily.

The 185 is the better match for dense, high-altitude beans. The wider bed allows you to grind slightly coarser without risking a rushed extraction. The extra volume of coffee absorbs the heat better, maintaining a stable temperature throughout the brew. This stability is crucial for extracting the complex acids and sugars in a dense Ethiopian natural or a washed Kenyan AA. The 185 gives you the room to let the water do its work without rushing to the exit holes. If you try to brew a dense, high-altitude bean in the 155, you will likely find yourself grinding finer to compensate for the smaller bed. This increases the surface area exposed to water, which can lead to astringency and bitterness because the finer particles over-extract before the center of the bed is fully saturated.

Conversely, the 155 is the superior choice for softer, lower-altitude beans. Brazilian, Colombian, and Sumatran coffees extract much more easily. In the 185, these beans can easily become over-extracted, pulling out harsh, woody, or ashy notes because the water sits in contact with the grounds for too long. The 155’s narrower geometry forces a faster flow rate, which matches the easy extraction profile of these softer beans. You can grind coarser in the 155, reducing the surface area and preventing over-extraction, while still achieving a clean, sweet cup. The 155 acts as a natural brake on extraction, keeping the cup bright and clear without the heavy body that the 185 might produce with these beans.

Grind Size and Flow Rate Dynamics

The grind size you use in the 185 will always be slightly finer than the grind size you use in the 155. This is not a preference; it is a physical necessity. Because the 185 has a larger diameter, the water has more distance to travel through the coffee bed. To ensure the water extracts enough solubles before exiting, you need a finer grind to increase the surface area and slow down the flow. If you use the same grind size in both drippers, the 185 will drain too slowly, leading to over-extraction and a muddy, bitter cup. The 155 will drain too quickly, leading to under-extraction and a sour, thin cup.

Flow rate is the primary variable you control with your pour. In the 185, you have more time to pour. You can use a slow, concentric pouring pattern, agitating the grounds gently to ensure even saturation. The flat bottom of the 185 allows you to control the flow rate by adjusting the height and speed of your kettle spout. In the 155, you have less margin for error. Your pour must be more deliberate and consistent. Because the bed is narrower, any unevenness in your pour will immediately affect the extraction of the outer edges of the bed. You cannot afford to skip the edges or flood the center. The 155 demands a more precise, controlled pour to ensure every particle is saturated evenly.

When to Choose Which Dripper

If you brew one cup at a time, or two, the 155 is the better investment. It is faster, more responsive, and easier to master. It forces you to develop a consistent pour technique because there is no room for error. If you prefer bright, acidic, tea-like coffees, especially those from Ethiopia or Kenya, the 155 will highlight those qualities without the heaviness that the 185 might introduce. It is the dripper for clarity and precision.

If you brew for three or more people, or if you prefer heavier, sweeter, more complex cups, the 185 is the better choice. The larger volume allows for better thermal stability, which is crucial when brewing dense, high-altitude beans. The 185 is more forgiving of minor pouring inconsistencies because the wider bed allows the water to redistribute itself more easily. It is the dripper for depth and complexity.

Ultimately, the choice between the Kalita Wave 185 and 155 is not about which one is better. It is about which one matches your brewing habits and your coffee preferences. The 185 is a tool for depth, stability, and complexity. The 155 is a tool for clarity, precision, and speed. Understanding the geometry of the flat bottom and how it interacts with the bean you are brewing will help you choose the right tool for the job. Stop guessing. Start matching the geometry to the bean.

Photo by Conor Brown on Unsplash.