Whereas the machines you see in cafes function in a lot the identical manner as they’ve completed for years, a quiet revolution is going down behind the scenes. This revolution is just not being led by the makers of espresso machines. The large leap in espresso know-how is one thing brilliantly easy, intuitive and reasonably priced. Are you able to guess what’s behind all of it? It’s the ‘excessive extraction’ filter basket.
After spending just a few weeks testing out a number of the new gamers within the ‘fancy filter basket’ house, we’ve seen some big enhancements within the style, extraction yield, and effectivity of our shot making. At a time the place the price of operating a restaurant is at an all time excessive, there may be immediately an enormous alternative for cafes to avoid wasting money and time. For anybody who’s contemplating a machine improve, maintain that thought for a second since you may very properly obtain the level-up in high quality you want for lower than a few hundred bucks.
Greater than a decade in the past, Vince Fedele set the gold commonplace for contemporary filter baskets with the launch of VST baskets. These had been revolutionary on the time, and had been quickly adopted in specialty espresso. Within the following years, this know-how didn’t see any important adjustments. However in simply the previous 12 months or two, a slew of challengers have immediately appeared, promising extra holes, sooner circulation, and better and extra even extractions.
Armed with this crop of latest baskets, higher distribution instruments — and an open thoughts in regards to the shot time and brew ratio wanted to make nice espresso — baristas are making totally different types of espresso, and pushing the envelope of extraction additional than ever earlier than.
New Children on the Diffusion Block
The new designs, by manufacturers such as Weber Workshops, Sworksdesign, and Wafo, operate on broadly similar principles. They are designed to have straighter sides, and for the basket holes to go as close as possible to the edge of the puck, allowing more even extraction of the coffee around the edge of the basket. They are made to tighter tolerances, and designed to warp less under the high pressures found in espresso machines. But the biggest difference, compared with previous filter baskets, is that they allow much faster flow, thereby allowing baristas to grind finer and extract higher than ever before.
The Sworksdesign Billet basket allows fast flow in an espresso, despite the tiny size of the exit holes.
Sheldon Wong, the founder of Sworksdesign, explains that the starting point for his basket design was to push for the holes at the bottom to cover the widest possible area, so that the entire puck can be extracted equally effectively. “The holes span a 57.5mm diameter area on my 58mm basket,” he says.
In older basket designs, on the other hand, the holes don’t extend all the way to the edge. “In regions without holes, water will flow to the bottom, hit a wall and then travel horizontally to find the nearest exit,” Sheldon says. “The flow velocity here will be slower than the water paths that happen to line up with a hole in the basket. Water will always prefer flowing through paths of less or least resistance — leading to locally higher extraction and leaving other areas under-extracted.”
The Sworksdesign Billet basket has straight sides and holes positioned close to the edge of the basket, to maximise extraction at the edge of the puck.
The Sworksdesign basket is machined from a solid piece of heat-treated 17-4 stainless steel — a particularly strong form of steel, usually found in turbine blades and rocket engines. Compared to standard baskets, which are stamped out of a thin sheet of lower-grade steel, these are better able to withstand the forces involved in espresso making. “[Coffee] particles push on the basket flooring with practically 250 kgs of pressure (or extra when above 9 bars) — it’s no surprise different baskets deform completely, even when made thick and heavy,” Sheldon says.
Excessive Velocity, Excessive Extraction
The brand new breed of basket designs declare to extend extraction, and there’s loads of proof (for instance from Lance Hedrick and Robert McKeon Aloe) on the market that they will do this below the proper situations.
We ran a fast take a look at of our personal, making an attempt out the usual Sworksdesign Billet basket in opposition to a traditional older basket from IMS, and had very related outcomes: the Billet required a finer grind measurement to achieve the identical shot time, and achieved significantly increased extractions — by practically three share factors. Our focus was on taking goal measurements, however because it occurs, the photographs from the Billet additionally tasted nice.
| Dose (g) | Yield (g) | Shot time (s) | Grind Setting (µm) | TDS% | EY% | |
| Sworks Billet | 16.2 | 44.3 | 18.3 | 140 | 7.9 | 21.9 |
| IMS | 16.2 | 43.2 | 19.0 | 172 | 7.0 | 19.1 |
The Sworks Billet enabled much higher extractions than the IMS filter. The difference was highly significant (T-test, p=0.016)
For these tests we used a Mazzer ZM grinder, a Dalla Corte Mina, and the 3065 Espresso Blend from Code Black. We also used a fast-extracting recipe (aka turbo shot), which may well be where this type of basket particularly excels. In fact, even at the finest setting possible — on a pair of burrs capable of grinding extremely fine — we still found the Sworks basket delivered fast shot times, and this high flow rate may well be the key to the high extractions that this type of basket allows. We also tried out the HE% baskets from Pesado compared to classic Pullman baskets, with similar results: while the Pullman baskets performed very well, the Pesado baskets allowed faster flow, averaging 6% higher extraction than the Pullman baskets in the tests we conducted.
But why do the new style of baskets allow faster flow? It’s not as simple as saying the basket has more holes, and therefore allows faster flow. The Sworks baskets have lots of holes, but the individual holes are very small — to the point that there may even be less open area at the bottom of the basket overall than in the IMS baskets.
Hole patterns in modern baskets. From top left: IMS, Pullman, Sworksdesign, Pesado HE%
Even if the total open area is similar, smaller holes create much more resistance. Regular readers may remember Poiseuille’s Law, which says that (assuming laminar flow), if you halve the radius of a pore, the resistance to flow increases by a whopping 16 times.
The length of the channel also matters: longer channels (i.e. holes in thicker baskets) create more resistance than shorter ones. In fact, Sheldon purposely kept the thickness of the Billet basket base lower than many other modern baskets, to reduce the amount of clogging. But many baskets feature conical holes, to reduce the effective length of the channel, making a comparison difficult.
Conical holes reduce the effective channel length of a basket. Where the hole starts to widen, it no longer adds significantly to the total resistance of the channel.
Unexpected Resistance
Calculating the effects of all the different variables that can affect the resistance of a basket is not straightforward, but the small holes and long channels of the Billet should mean that it puts up a lot of resistance to flow, when in fact the opposite is the case.
Why would this be? We can only assume that when brewing an espresso, the design of the holes somehow reduces clogging and blockage by fines — but then, plenty of users have reported that very small holes in the filter basket become easily blocked by small coffee particles, making this style of basket much harder to clean.
A coffee particle stuck in one of the holes at the bottom of an Sworks basket, as seen through a microscope in Lance Hedrick’s video review of modern baskets.
To resolve this contradiction, we will need more information. Firstly, we want to try testing these baskets using coffee with the fines completely removed, in order to understand the role that fines play. Much easier said than done, since static cling means that sieving can’t dislodge the smallest particles, but we have some potential ideas to make this possible that we hope to explore in a future post.
More importantly, we need a better way to analyse the basket holes themselves. To this end, Professor Abbott is working on an app to calculate the size of filter basket holes from a photo, inspired by this insightful post by Robert McKeon Aloe. Understanding why these baskets perform so well could be the first step towards optimising their design even further. Until then, you’ll find us enjoying faster shots than ever, thanks to the new breed of fast-flow baskets.
