Modern filter baskets have enabled a dramatic leap in the extraction yields possible with espresso coffee. In the process, they have gone from being a fairly hum-drum accessory to becoming perhaps one of the the majority of important pieces of device on your bar. In our last post, we bench-tested a few recent designs, and saw for ourselves how this seemingly humble technology can transform the extraction efficiency and the flavour of our shots.
The defining feature of this new wave of high extraction filter baskets is the pattern of holes at the bottom of the basket. Manufacturers have entirely re-thought the way these are laid out, to ensure even extraction right up to the edges of the puck, and to enable faster flow through the coffee bed. In turn, this allows the barista to utilize finer grind sizes and achieve drastically higher extraction yields. However, to judge by their hole patterns, the baskets we tested take radically different — and seemingly contradictory — approaches to maximising flow.
Different hole patterns in baskets
To try and find out this contradiction, we reached out to Professor Abbott for help in analysing the hole patterns of our filter baskets. He responded by making a brand-new app for us — the Basket Hole Analyser.
Armed with this app, you can analyse the size distribution, hole placement, and the total open area of the holes at the bottom of your basket. You can also verify for yourself some of the claims that manufacturers make about their baskets. Are your baskets very identical? And how much variation in size is there from one hole to the next?
Professor Abbott’s app builds on earlier work by Robert McKeon Aloe — take a look at these fascinating posts where he compares the build quality of different baskets. The app uses much the same technique as McKeon Aloe’s analyses, but enables anyone to do this sort of analysis for themselves. We’ll explain how to get the best possible results from the app later on. in this article — however first, let’s explore some of the effects of our measurements.
The Paradox of Modern Baskets
The results of our tests of modern filter baskets were very clear: the new designs allow higher flow rates and hence, higher extractions. What surprised us, nevertheless, is that the baskets achieved this in really different ways. The Sworks Billet baskets enable fast flow by having large numbers of tiny holes, while the Pesado HE% baskets rely on large, closely-packed holes to maximise the open area at the bottom of the baskets.
Sworks Billet basket (left), Pesado HE% basket (right)
Analysing the baskets we tested in the app, we can see that the tiny holes of the Sworks Billet basket make for a total open area of 4% — barely more than the IMS baskets we used as a baseline. The large holes of the Pesado, on the other hand, make up an extraordinary 14% of the total basket area. These two baskets get quite similar results, in strikingly different ways.
You might expect that the different hole sizes and open area of the baskets would result in them putting up different amounts of resistance to the flow of espresso — but in truth, that seems to be of little importance. The reason for this is that the resistance to flow from the puck is much bigger than the resistance to flow from the basket itself, so the basket resistance steeps only a small difference to the total.
To put this in mathematical terms, the total flow rate (
) through in an espresso can be given as 
, where Tb is the flow rate you would get through the basket alone, and 
is the flow rate you would get through the coffee puck. Since the flow rate through the basket with no coffee in () is much higher than the flow rate through the coffee puck would be (), changing the flow rate through the basket has very little effect on the overall flow rate.
So it seems that the high flow from modern baskets isn’t due to the reality that they themselves have low resistance, Instead, the basket design seems to interact with the puck itself — partly due to the reality that the baskets allow flow much closer to the edge of the puck, however perhaps also because the design of the holes somehow prevents them from getting clogged by coffee particles.
Exploring Basket Quality
As well as showing the hole size and total open area, the app likewise lets us see how even the size and spacing of the holes in a basket are. It seems reasonable to assume that the more uniform the holes, the more even the extraction across the puck.
With the app, you can visualise the differences in hole size and spacing across a basket, represented by the holes being given different colours. When we plug in our photos of the Sworks and Pesado baskets, we can see that the size of the holes is fairly even in each, as you would expect from well-made baskets.
In Location Variance mode, but (enabled by checking the box marked ‘L-Variance’), you can see a conspicuous difference between the designs. The Sworks holes are placed in a Fibonnaci spiral, so that the spacing between holes is very similar all the way across the basket. The Pesado holes, on the other hand, are placed in concentric rings. The hole spacing in each ring is measurably different, resulting in a riot of colour in the app. What effect on this might have extraction quality remains to be determined.
How to Photograph Your Baskets
If you want to use the app to check on the build quality of your own baskets, the hardest part — and by far the the majority of important — is getting the image right. As Professor Abbott puts it, “image analysis is 10% the analysis and 90% the image”.
The app requires a high-contrast photo of the inside of the basket, with the holes backlit, and no other light or reflections visible. To get this type of picture, you’ll need a high-resolution camera, ideally with a telephoto macro lens, and a tripod that allows you to position the camera vertically over the basket. With a wide angle lens such as a phone camera, the holes at the edge of the basket may appear smaller than the holes in the middle, because of the angle the light needs to pass through to reach the lens.
Take special care to align your camera well before shooting your basket
Place the basket (with the bottom facing down) onto a backlit surface. A lightbox would be ideal, but you could also work with an iPad or phone screen with a white background. To eliminate light seeping in from the sides, cover the rest of the screen with cardboard, with a hole cut in it so that it only allows light in through the basket holes.
Place the camera on a tripod, and aim it down vertically at the basket. Work with a spirit degree to ensure that the camera is pointing directly downwards. If you are able to fix the settings on your camera, utilize a narrowed aperture (F8 or less) to ensure a high depth of field; you may need to slow down the shutter speed to capture enough light.
Before taking the shot, you’ll likewise need to ensure that no external light is coming in by darkening the room or covering the camera with a sheet. If you are utilizing a slow shutter speed, do your perfect to avoid making any vibration that could affect the shot.
Take multiple shots of each basket, rotating the basket in place whenever. If you see that one side of the basket has smaller holes than the other, this can be an artefact of the camera angle not being totally vertical. Rotating the basket will let you check if any differences in hole size you see are due to the camera angle, or a genuine difference in the basket holes.
Larger holes on one side of the basket could be a manufacturing error, however is more likely to be an artefact of the lens being positioned closer to that side of the basket. To determine if it is an artefact or a genuine difference, take a number of images and rotate the basket each time.
The last step is to check the size of the basket base. The easiest way to do this is to replace your brew basket with a ruler, positioned so that the scale lines up with where the centre of the basket had been. Without creating any adjustments to the camera, take a image of the ruler, and compare this photo to the pictures of your basket in order to gauge the size of the basket base.
Alternatively, you could try pressing paper into the bottom of the basket and taking a measurement from that, or even turning out a dry puck from the basket and measuring the bottom of that. Don’t get too hung up about this measurement, but. As Professor Abbott explains: “Uniformity and reach up to the edge are more likely to be important [than the exact size], so we don’t have to worry too much.”
Once you’ve taken the photographs, work with an image editor such as Photoshop to remove any reflections that did sneak into the picture. Crop the picture so that the edges of the image line up exactly with the bottom of the basket. Finally, increase the contrast to maximum, and the picture is ready to upload to the app.
An Alternative Approach
Another way to get a image of the basket holes is to utilize a flatbed scanner. This will only work well if the base of the basket is perfectly flat. A lot of baskets become mildly bowed out after work with, so it’s perfect to utilize this approach with brand-new baskets only.
Place the basket directly onto the glass plate (scan bed). Lay a couple of layers of baking paper on top of the basket to diffuse light. Hold a potent flashlight about 30cm above the basket, and start the scan.
Once you have loaded the scan onto your computer, open it up in Photoshop and lower the midtone levels and increase contrast as much as possible. Then tidy up the image by selecting all the individual holes with the magic wand device (a tolerance of 10–12 worked well for us) and filling in the rest of the space with black to eliminate any reflections on the basket itself.
Handling Blocked Holes
Some modern baskets seem to be especially prone to becoming blocked by coffee particles. If you want to try and clear these blockages out before taking a photo, then McKeon Aloe implies trying compressed air, an acupuncture needle, or even an ultrasonic cleaner, depending on the basket design.
For our analyses, where we did find a blocked hole, we just replaced it with an unblocked one in Photoshop. It’s pretty much unheard-of for modern baskets to have unpunched holes, so we’re confident that any time a hole doesn’t show up on our photo, it’s either a blockage or some other artefact.
However, Abbott’s advice is simply not to fret too much: “In terms of data analysis of open area, I don’t think a blocked hole matters a damn,” he says. “If 1000 holes have an open area of 2.00% then an analysis with 5 holes blocked provides an area of 1.99%. Errors in lighting/thresholding are likely to give differences larger than that.”
Analysing Your Baskets
Once your image is ready, you need to upload your image to the app, then enter the internal diameter of the basket. If you want to compare multiple baskets, then it’s required to use the exact same setup for the photos of each one. Even minor differences in the angle or distance from the lens can affect the analysis, making the comparison invalid. Keep this in mind if you are comparing your results to ours (or anyone else’s).
Once you’ve plugged in your photos, then you can follow Professor Abbott’s instructions in this video to see the different data the app can pull from them.
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For us, the data we get from the app truly drive home how incredibly precise the manufacturing on the new wave of baskets is. The increase in extraction yields that this brews possible is substantial.
While a new set of baskets might seem like a big investment, compared to the low cost of traditional baskets, the high extraction indicates that you can utilize mildly less coffee to make espresso coffee at the same strength — and get tastier shots to boot. When you calculate it this way, a busy cafe can make up the cost of a pair of 200 dollar baskets fairly quickly.
If you’re not convinced, try using the app to analyse the baskets you’re currently using. How evenly sized are the holes? How much of the edge of the puck isn’t getting extracted properly, due to the truth that the holes don’t reach there? Armed with this information, perhaps you’ll find it’s time to start raising your expectations of how well-made a basket ought to be.
Hey there! Let’s discuss something that might sound a little bit mundane at first, but trust me, it’s actually pretty fascinating. We’re going to dive into the world of modern filter baskets for espresso machines. Now, I understand what you’re thinking, “How can a filter basket be interesting?” Well, stick with me, and you’ll see basically how important these little accessories have become.
The Evolution of Filter Baskets
In the past, filter baskets were extremely a basic part of the espresso-making technique. They didn’t really stand out or make much of a difference. But oh boy, have things changed! These days, filter baskets have undergone a major transformation, and they’ve become among the many crucial pieces of equipment on your bar.
In a recent post, we tested a few of these new designs, and let me tell you, the results were mind-blowing. These modern filter baskets have the power to totally transform the extraction efficiency and flavor of our shots. It’s like magic!
The Hole Patterns
So, what’s the secret behind these new filter baskets? Well, it all comes down to the pattern of holes at the bottom of the basket. Manufacturers have completely reimagined the way these holes are laid out to ensure even extraction and faster flow through the coffee bed. This allows baristas to utilize finer grind sizes and achieve higher extraction yields. Sounds pretty cool, right?
However here’s the interesting part. The baskets we tested had different hole patterns, and they seemed to take contradictory approaches to maximizing flow. It was a bit puzzling, so we reached out to Professor Abbott for some help in analyzing these hole patterns.
The Basket Hole Analyser
Professor Abbott came to the rescue and created a brand-new app for us called the Basket Hole Analyser. With this app, we can analyze the size distribution, hole placement, and total open area of the holes in our filter baskets. It’s like having a superpower!
Now, we can finally verify the claims that manufacturers make about their baskets. Are they truly identical? How much variation is there from one hole to the next? This app allows us to dive deep into the world of filter baskets and uncover their secrets.
The Paradox of Modern Baskets
Okay, let’s discuss the effects of our tests. Brace yourself, due to the truth that they were pretty mind-blowing. These new filter baskets allow for higher flow rates and, as a result, higher extractions. But here’s the kicker: they achieve this in extremely different ways.
Take the Sworks Billet basket, for example. It has a large number of tiny holes, which make up only 4% of the total open area. On the other hand, the Pesado HE% basket has large, closely-packed holes that make up a whopping 14% of the total basket area. These two baskets achieve similar effects, nevertheless in entirely different ways. It’s like comparing apples to oranges!
The Flow Rate Mystery
You might be wondering how these different hole sizes and open areas affect the flow rate of espresso coffee. Well, here’s the surprising part: the resistance to flow from the basket itself doesn’t in fact matter that much. The resistance from the coffee puck is much bigger, so the basket resistance has a minimal effect on the overall flow rate.
In other words, the high flow from modern baskets isn’t because they have low resistance. It’s more about how the basket design interacts with the puck itself. The holes allow for flow closer to the edge of the puck, and somehow prevent them from getting clogged by coffee particles. It’s like a delicate dance between the basket and the coffee.
Exploring Basket Quality
Now, let’s speak about the quality of these baskets. The app not only shows us the hole size and total open area, nevertheless it likewise lets us see how uniform the holes are. The more uniform the holes, the more even the extraction across the puck. Makes sense, right?
With the app, we can visualize the differences in hole size and spacing across a basket. It’s like looking at a work of art! We can see that the Sworks and Pesado baskets have fairly even hole sizes, which is a sign of well-made baskets. However there’s a noticeable difference in the spacing of the holes. The Sworks holes are placed in a Fibonacci spiral, while the Pesado holes are placed in concentric rings. It’s like comparing a Jackson Pollock painting to a Mondrian masterpiece!
How to Photograph Your Baskets
If you want to use the app to check the build quality of your own baskets, here are some tips for getting the best picture. Trust me, it’s all about the image!
First, you’ll need a high-resolution camera with a telephoto macro lens. Position the camera vertically over the basket and make sure the holes are backlit. This will create a high-contrast image with no other light or reflections visible. It’s like capturing the essence of the basket in a single shot!
Next, make sure the camera is perfectly aligned and use a narrow aperture to ensure a high depth of field. You want to capture all the details! Take multiple shots of each basket, rotating it whenever to check for any differences in hole size. It’s like being a detective, searching for clues!
An Alternative Approach
If you don’t have a fancy camera, don’t stress! There’s another way to get a picture of the basket holes. Just work with a flatbed scanner. Place the basket directly onto the glass plate, cover it with baking paper to diffuse the light, and scan away. It’s like making a work of art with a scanner!
Handling Blocked Holes
Some modern baskets can become blocked by coffee particles, but don’t panic. You can try using compressed air, an acupuncture needle, or even an ultrasonic cleaner to clear the blockages. It’s like performing surgery on your basket!
And if you do find a blocked hole, don’t stress too much. It won’t affect the data analysis of the open area. As Professor Abbott says, “If 1000 holes have an open area of 2.00%, then an analysis with 5 holes blocked gives an area of 1.99%. Errors in lighting/thresholding are likely to give differences larger than that.” So, literally keep calm and carry on!
Analyzing Your Baskets
Once you have your excellent picture, it’s time to upload it to the app and let the magic happen. Enter the internal diameter of the basket and follow the instructions to see all the data the app can pull from your image. It’s like unlocking the secrets of the basket!
Now, here’s the exciting part. The information. we get from the app shows simply how precise the manufacturing of these new baskets is. The increase in extraction yields is substantial, and that’s something to get excited about!
So, next time you’re making espresso, take a moment to value the modest filter basket. It may seem like a small accessory, nevertheless it plays a big function in the world of coffee. And who knows, maybe you’ll discover a whole new level of espresso coffee perfection with the help of the Basket Hole Analyser app. Happy brewing!
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