Espresso baskets vary by their hole area and by how much they can be filled. The grind required for a given basket depends on the ratio of coffee weight to hole area. If you use more coffee, or a basket with reduced hole area, a coarser grind is needed.

Below is a table giving the hole area and volume of five common baskets. I urge people to send me the equivalent data on other baskets, and I'll be happy to add them.

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BASKET      HOLE.DI   VOLUME  HOLE.AREA  V/A   V/A.ADJ  DOSE.ADJ
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E61 1         28.4      57.9     8.07    7.17   1.72     0.45
E61 2         42.5      75.1    18.06    4.17   1.00     1.00
LM 1          31.2      59.4     9.73    6.10   1.47     0.54
LM 2          42.5      75.2    18.06    4.16   1.00     1.00
LM.OEM 2*     43.0      83.1    18.49    4.49   1.08     1.02
OEM 3         49.1      91.6    24.01    3.82   0.92     1.33
SPAZ 2*       43.0      80.2    18.49    4.34   1.04     1.02
VST 18*       49.5      79.2    24.51    3.23   0.78     1.36
VST 15        48.8      71.7    19.50^   3.68^  0.88^    1.08^
VST 18        48.8      76.7    19.50^   3.93^  0.94^    1.08^
VST 22        48.8      88.1    19.50^   4.52^  1.09^    1.08^
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* data contributed by HBers

^ VST baskets have smaller hole diameters and more holes, so the punch area is misleading. These figures are estimates based on dose to grind setting measurements

The raw data is given on the first two columns.

The first is a micrometer measurement of the diameter of the punched hole area. The pattern is a polygon, and the measure goes between parallel straight edges, not corner to corner. As Andy Schecter has pointed out, the QC on many baskets is poor, and using this measurement to estimate hole area will create random errors from basket to basket of the same manufacturer. However, it gives an idea how different kinds of baskets compare, and it is easy to do.

The second column is basket volume, given as the gram weight of table salt required to fill each basket to the rim. I use table salt rather than ground coffee since it is less mess and less variable. I tared the baskets, put them in a bowl, overfilled them with table salt, leveled the salt off, and weighed. I figure this is a procedure as easy to standardize as the punch area diameter measure for hole area.

The third column is the first column divided by ten and squared, giving a measure of the punched hole area. The very last, sixth column, divides each of these area with the E61 and ridged LM double area (which I take as standards since everyone has a few). If you move between baskets, this column tells you how to adjust the dose to keep the grind setting roughly the same.

The fourth column is the volume divided by area, and the fifth again normalizes this so the E61 and LM doubles are at 1.00. These columns gives an idea of how far a basket can be updosed, and how coarse a grind can be used to make a shot. The coarsest grind possible for espresso occurs in single baskets, since they have a tapered shape. On the other hand, if you want to grind very fine and eliminate as much headroom as possible, the VST or triple basket is your best bet.

I didn't realize the salt method was so inaccurate. Anyone have a more accurate procedure that's equally accessible?

I turned the basket upside down, look for parallel lines on the outermost row of the polygonal lattice of holes, and put the calipers along the outer edge of the holes themselves.

When the basket discussions started, it became clear that almost all the manufacturers use exactly the same punch out technology, so that the nominal spacing and size of the holes are the same for all conventional baskets. I have had good luck using the punch area, as measured here, to come up with the dose ranges required by each basket to stay within my preferred grind range.

If VST uses a punch with different hole sizes or spacing, the larger area may not translate to a finer grind requirement or higher dose requirement. The prediction from the measurement is that the 18 gram nominal dose in the VST would need the same grinder setting as a 13.2 gram dose in an LM ridged double or an E61 basket (18 grams divided by the 1.36 dose adjustment). Some of the posters to the VST thread have indicated that dosing changes along these lines are the case, but others have had no such result.

When I get the VST baskets, I'll see if the equal grind dose adjustment is close to the predicted level from the punch measurement. If it is, they use the conventional hole size and spacing, albeit with more precision; if not, then the lattice geometry has also been altered from the conventional setup. In the mean time, others are welcome to test these predictions.

RapidCoffee wrote:I'm sure we will see salt weight differences due to moisture content. Taping the bottom of the basket and filling with water would probably be more accurate.

The volume is the less critical measure, since it just indicates the headroom and updosing potential of a given basket. I suppose a 5% error is not too bad, given the use.

The hole area on the other hand, is needed to estimate grind or dose changes; so increases in accuracy here would be very useful.

Jim,

Very interesting data. You're only interested in standard 58 mm baskets, right? No need to measure the smaller home lever baskets?

I want them all. Here's a for instance:

How different is your lever from a regular machine in terms of grind requirements. Suppose you grind coffee for a good shot on your pump machine. Then you use the conversion based on hole area to load the equivalent dose/same grind into your lever basket. If the resulting shot is a gusher or a choke it tells you something about the lever group. The NS Athena (Astoria group) required an extra fine grind when using normal baskets, so the idea is not a stretch.