Billet baskets with holes that actually go all the way to the edge!
Traditional baskets are economically mass produced by stamping thin sheets of metal which require a large radius at the bottom edge. The thin material combined with high pressure extractions place the holes away from the outer edge for stress/deformation issues. They also have curved bottoms because it would deform permanently after the first few uses anyways as the material work hardens.
In my design, I set out on a no compromise approach with holes all the way to the edge - not just close enough! If this was done on standard 300 series stainless steel, it would deform and eventually crack. Rather than simply making the basket thicker and heavier*, I use 17-4 stainless steel, a martensitic precipitation hardened material that is traditionally reserved for turbine blades, food processing equipment, gears/shafts or rocket engines which require high strength, hardness and corrosion resistance. To put this in numbers, the tensile yield stress of hardened 17-4 can be >190,000 psi whereas 316 is only ~35,000 psi. Stainless steel grinder burrs have a hardness rating of ~50 HRC. 17-4 can be hardened to >43 HRC while 316 is so soft, it doesn't even register on the HRC scale. Another important difference is that while 17-4 has excellent corrosion resistance, it's magnetic! Something that is important to the home barista. Not only will your magnetic accessories like funnels and my PorcuPress continue to work, they will now work even better.
Why am I telling you this? Because if you followed me this far, you might find this interesting as I am trying to bring my aerospace experience to the world of coffee! You probably also want to know where all your money is going...
*Increasing thickness adds unwanted thermal mass and increases the likelihood of clogging
The manufacturing process is long and extensive. It starts with a nearly 1kg solid block of 17-4 (which the raw material alone cost more than a high end stamped basket) and hogged away in the hardened state leaving just ~45g behind - the metal removed is recycled into raw material. Due to the complex processes involved, these baskets have an unconventional flat lip and take many hours to produce each one.
*New shower screen is required to use with the Picopresso
*Actual volume capacity will vary with grind size, roast level, humidity, etc
Pattern Tasting Notes*
Reduced/Standard/High Flow: Uniform round hole patterns in three different hole packing densities arranged in a Fibonacci spiral. Reduced Flow has a lower number of holes matching high end stamped baskets but reaches out to the edge as expected. This aims for a more typical flavour profile without having to grind very fine. Standard Flow features the same hole spacing as stamped baskets but packs a lot more holes since they go all the way to the edge. Both are great for milk drinks and traditional espresso for a more blended taste profile while seeing an extraction bump. High Flow gets interesting as the hole count increases drastically and typically have an even higher extraction bump. I use this for milk drinks too without fail but shines with light roasts and long ratio pulls. Expect increased acidity and clarity.
Citrus Slice: It looks like a cut of citrus! Testing this one with friends, we found increased acidity over the high flow pattern that was clean, clear and fruit forward.
Variable Flow - Midbelt/Edge Bias: Different regions of the puck produce different levels of perceived acidity/sweetness/bitterness/etc. We found that different coffees and roast levels greatly alter the results of these baskets (compared to the standard/high flow as an example comparison) but generally speaking - Midbelt Bias rounds out the peak acidity just taking the edge off of coffees that seem to attack your taste buds as well as taming astringency. Edge Bias increased bandwidth on acidity without spiking higher.
*Based on my personal testing
Paper filters are not required but available here if you prefer to use them