Hi guys.

Over the months and years, various threads have included sundry curses and facts on single baskets, so I figured it may be helpful to have a thread on the topic.

The profile of the basket, to me, seems important, and I would have thought a relatively rectangular profile (such as on the LM) would be the way to go. Such a shape would allows even pressure to be exerted all the way through without any basket shape anomalies interfering. I always wondered why single baskets werent the same design as a double, but half the depth, rather than being the irregular shape they are:

Double and single baskets from Rancilio Silvia

Double and single baskets from La Marzocco

Double and single baskets from La Pavoni, also used on Imat/Quaha and some others

On reflection, the reason seems obvious. A filter basket must have a certain combination of diameter and depth, matched to pump pressure, to allow a full load of typical espresso grind to produce about the right extraction time. A basket too deep for its diameter would require a coarser grind or a lighter tamp to offset the extra depth, and a basket too shallow for its diameter would need the opposite. That being the case, with a rectangular profile, there would only be one possible perfect depth for a given diameter basket, and I feel machine manufacturers make the double basket to basically meet this formula.

Because in the domestic market at least theres a demand for single baskets, theyve had to make some compromises on that formula to allow a basket with half the coffee to produce roughly the same extraction times with the same grind as whats needed for the double. Considering the depth / diameter equation, this could be achieved by keeping the depth the same and halving the surface area (~diameter), or halving the diameter and maintaining the surface area (~diameter). Since the top basket diameter must match the double basket for correct fitment to the group, the option most choose is to reduce the diameter of the basket by roughly half and keep the depth similar. Of course, the opening needs to be the same size to allow correct fitment to the group, so they start at 58mm and then cut in to take it down to its final diameter which is around the 35mm mark.

This causes a plateau at the outside of the basket about 10-15mm from the top of the basket which complicates the tamping process. Its impossible to tamp all the coffee to the same pressure when the basket shape causes some areas to accept more pressure than others. Also, the different depths mean there are different length paths for the water to travel; water entering at the outside will have to run through the high pressure stuff at the outside, then come in and continue through the low pressure coffee in the bottom well; water entering in the middle takes the quicker path straight through the centre. And Im sure there are other reasons too.

Suspected pressure in a double basket before and after tamping

Suspected pressure in a single basket before and after tamping

A final word: none of this means single baskets are impossible to produce decent coffee with, but it does make it more difficult, and it does depend on the machine. I produced acceptable results with the single in the time I had my Quaha, but I find it much harder with the Silvia due to its lower showerscreen.

Look forward to hearing what others have to say!

Greg

Over the months and years, various threads have included sundry curses and facts on single baskets, so I figured it may be helpful to have a thread on the topic.

The profile of the basket, to me, seems important, and I would have thought a relatively rectangular profile (such as on the LM) would be the way to go. Such a shape would allows even pressure to be exerted all the way through without any basket shape anomalies interfering. I always wondered why single baskets werent the same design as a double, but half the depth, rather than being the irregular shape they are:

Double and single baskets from Rancilio Silvia

Double and single baskets from La Marzocco

Double and single baskets from La Pavoni, also used on Imat/Quaha and some others

On reflection, the reason seems obvious. A filter basket must have a certain combination of diameter and depth, matched to pump pressure, to allow a full load of typical espresso grind to produce about the right extraction time. A basket too deep for its diameter would require a coarser grind or a lighter tamp to offset the extra depth, and a basket too shallow for its diameter would need the opposite. That being the case, with a rectangular profile, there would only be one possible perfect depth for a given diameter basket, and I feel machine manufacturers make the double basket to basically meet this formula.

Because in the domestic market at least theres a demand for single baskets, theyve had to make some compromises on that formula to allow a basket with half the coffee to produce roughly the same extraction times with the same grind as whats needed for the double. Considering the depth / diameter equation, this could be achieved by keeping the depth the same and halving the surface area (~diameter), or halving the diameter and maintaining the surface area (~diameter). Since the top basket diameter must match the double basket for correct fitment to the group, the option most choose is to reduce the diameter of the basket by roughly half and keep the depth similar. Of course, the opening needs to be the same size to allow correct fitment to the group, so they start at 58mm and then cut in to take it down to its final diameter which is around the 35mm mark.

This causes a plateau at the outside of the basket about 10-15mm from the top of the basket which complicates the tamping process. Its impossible to tamp all the coffee to the same pressure when the basket shape causes some areas to accept more pressure than others. Also, the different depths mean there are different length paths for the water to travel; water entering at the outside will have to run through the high pressure stuff at the outside, then come in and continue through the low pressure coffee in the bottom well; water entering in the middle takes the quicker path straight through the centre. And Im sure there are other reasons too.

Suspected pressure in a double basket before and after tamping

Suspected pressure in a single basket before and after tamping

A final word: none of this means single baskets are impossible to produce decent coffee with, but it does make it more difficult, and it does depend on the machine. I produced acceptable results with the single in the time I had my Quaha, but I find it much harder with the Silvia due to its lower showerscreen.

Look forward to hearing what others have to say!

Greg

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