Espresso Basket Size
One of the most important things to achieve in making great-tasting espresso is using the full range of ratios (1:1 – 1:4), and to accomplish this, you will have to use the full range of doses (14g-25g).
Yield = dose * ratio
If you have a light roast coffee that requires a 1:4 ratio, with a 20g basket, you would need a yield of 80g. For some espresso machines, that isn’t easy.
If you drop the dose to 14g, the yield required becomes 56g – much more achievable. But putting a 14g dose in a 20g basket has four problems:
- The bed depth is too shallow. A thinner coffee bed presents less flow resistance; your shot will run faster. You can grind it finer to try to slow it down, but the water still needs some space to get through. If your coffee is ground too fine, the tamped grounds can pack too tightly together, and the pressure in your machine may not be able to push water through, resulting in either a backed-up machine or overly extracted espresso with a bitter flavor.
- Too much head space. The headspace must be filled with water before any pressure can build up in the puck. While the headspace is filling at 0 bars, the puck is already starting to absorb water, creating a pre-infusion effect. A bigger headspace allows a longer time for the grinds to saturate before full pressure is reached, resulting in the flow running faster at the end. It also leaves you with soggy pucks.
- Too many holes. With a shallower bed and less resistance, you need fewer holes to maintain resistance.
- The holes are too big. With a shallower bed, less resistance, and a finer grind, the hole sizes must be reduced to maintain resistance for contact time.
The better option is to use a 15g VST Precision basket, which has fewer and smaller holes than a 20g basket, increasing the resistance, so you don’t have to grind as fine to achieve the extraction time. It also solves the headspace problem.
At the other end of the roast spectrum, if you have a very dark roast that requires a 1:1 ratio with a 20g basket, you will only get a yield of 20g. The better option is to use a 25g basket VST Precision Basket; you can increase the dose and get a 25g yield – much better.
The 25g VST Precision basket has bigger holes, and more of them than the 20g basket, so the resistance and grind size can remain relatively constant.
Your dose should be +/- 1g of the basket size to get the right headspace.
When you have a choice of baskets, for example, with a 19g dose that could use either an 18g or 20g basket, use the smaller basket because you won’t have to grind as fine.
The Espresso Filter Basket is an important tool. A set of VST Precision baskets, 15, 18, 20, 22 and 25g, will help you cope with the full range of ratios, doses and yields required.
Precision espresso basket
The shape of both the basket and its holes can have a significant impact on extraction and flavour. Getting great filter baskets is a small investment that can make a huge difference.
Precision baskets have much less hole variability than the standard basket
Precision baskets do make an appreciable difference to extraction levels and uniformity. They’re a great way to not only improve your extraction, but also the overall taste of your espresso.
Some of the major precision basket brands are: VST espresso basket, IMS espresso basket, Pullman espresso basket, Strada filter baskets.
VST espresso basket
My choice was the VST Precision baskets.
VST Precision Filter Baskets are optimized for use with specific capacities in the dose weight of coffee. The size of the holes, the number, and placement vary across the basket sizes to deliver consistent extraction performance.
VST baskets produce significantly more consistent results than OEM baskets. See https://clivecoffee.com/blogs/learn/portafilter-baskets-do-they-matter
VST Precision Filter Baskets are available in 7, 15, 18, 20, 22 and 25-gram capacities.
All baskets feature…
- Unmatched Quality Control: 100% of holes are measured on every filter for min/max
range and hard limits on area and diameter to a precision of better than +/- 30 µm - All holes are measured for circularity, placement, square area, and blocked holes.
- Filters are matched for total square area opening to +/- 5% to ensure identical group-to-group
(Typical filters vary from -50 to +100%) - The hole pattern is centered to +/- 1.0 mm, and placement is
oriented for uniform extraction throughout the entire puck. - The wide outlet angle prevents clogging, and the anti-wear design
ensures uniform extraction performance for the product’s life. - Improved structural integrity, 20% heavier than standard filters,
highly polished inside treatment and profile for a clean knock-out
Ridged vs Ridge less baskets
Ridged filter baskets have a groove in the side wall, which a spring in the portafilter locks in to help retain the basket in the portafilter. Ridgeless, or unridged baskets, have smooth walls and, as a result, generally require a stronger spring to ensure they stay in place when knocking out used coffee pucks.
Having no ridge means the puck knocks out cleaner, and a ridge will affect the fluid flow in the puck.
Ridgeless is the one to go for.
What effect does portafilter diameter have on espresso?
Different espresso machines can have different diameter portafilters. The most common size is 58mm, but there is 49mm and everything in between. The major difference is at a standard 8 bars of pressure, the larger basket has more extraction force applied.
Scientifically, pressure applied is normally measured as force per unit surface area. Taking the bed of coffee as a flat surface, and we assume traditional extraction pressure of 8 bar, the net extraction force upon the coffee puck will be greater for larger surfaces.
8 bar = 800kPa = 800 kN/m2
Given two different basket sizes 58mm and 52mm, which are 0.058m and 0.052m, respectively, the net force on the surface of the bed of coffee will be:
For 58mm:
Surface area: πr2 = π*0.0292 = 0.00264207942
Net force on area: pressure x area = 800*0.00264 = 2.11 kN
For 52mm:
Surface area: πr2 = π*0.0262 = 0.00212371663
Net force on area: pressure x area = 800*0.00212 = 1.7 kN
The larger portafilter is subject to a higher extraction force with the same pressure.
This should tend towards better consistency in extraction because more of the coffee is in contact with the water at the bed surface, and so has a more direct pressure gradient through the puck, as it will be comparatively thin in the larger basket helping to reduce the probability of channelling.
Plus, there are just more options available for 58mm, so get a 58mm machine if you can.
Pressurized espresso basket
A pressurized basket only has a single hole in the bottom. Often, they have indentations to make them look like a normal basket with lots of holes, but if you hold them up to the light, you will see only one hole.
This is so the basket itself supplies all the resistance, and you can use pre-ground coffee in an espresso machine.
If you have a pressurised espresso basket, get rid of it, and get yourself a better grinder.
Single espresso baskets
It is designed to hold what is known as a single dose of 7g. It is cone-shaped with a much smaller area at the bottom.
They are difficult to work with, difficult to prep, difficult to brew with evenly, and difficult to knock out. Outside of Italy, the single dose basket is generally not used.
What is a bottomless portafilter?
The bottomless or naked portafilter is a portafilter without spouts, so the bottom of the basket is exposed. This enables you to use a mirror and watch the extraction process.
The main advantage of this is that you can observe any rogue streams of espresso caused by channelling. With a manual lever espresso, you can immediately take action, easing off the pressure to stop the spurt, then bring the pressure gently back up.
Bottomless portafilters are also easier to keep clean and, therefore taste better, have better crema because there is less contact with the surface of the spout, and help you develop consistent puck prep, distribution and tamping.
Holes to the edge baskets
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 to prevent deformation.
There are several companies now creating baskets with holes to the edge to get a more even extraction, massive flow rates, allow finer grinding, and increase extraction yields. I have not tried any of these baskets yet, but I am particularly interested in the WAFO Spirit.
Holes to the edges, lots of holes 3000, more even extraction, massive flow rate.
The Future of Espresso? | WAFO Espresso Baskets Intro (youtube.com)
Edge extraction, “volcano” effect and better baskets – Caffeinated Science
WAFO vs Unifilter vs VST: Espresso Basket Comparison (youtube.com)
2. Billet Basket (sworksdesign.com)
3. Unibasket – Weber Workshops
Additional information...
Espresso Machine Baskets Explained (youtube.com)
Wet Coffee Puck – Is Watery Espresso Puck a Problem? (baristahustle.com)
Espresso Headspace – Barista Hustle
How filter baskets affect espresso taste and barista technique (home-barista.com)
Espresso Baskets: Precision vs. Regular | by Robert McKeon Aloe | Towards Data Science
