The purpose of tamping is to lock in coffee particle distribution, polish the surface of the bed and eliminate any compartments within the coffee bed. Generally, it is advised that baristas tamp with between 30-40 pounds of force. If you so desired, as some do, you can place a bathroom scale on the counter to determine the amount of pressure to apply to equal a minimum of 30 pounds.
To tamp, grip the tamper in your hand and align the shaft of the handle as if it were an extension of your forearm. The base of the tamper should fit comfortably within your palm. While keeping the tamper level, press it onto the coffee bed and exert a minimal required force to compress the grounds (this comes with practice). Remember, additional force applied is not nearly as important as evenness and consistency of force.
Then lift up the tamper to inspect the coffee bed and ensure a level tamp has been achieved. If there are remaining spaces that need to be tamped, perform the tamping action again. Since all tampers are slightly smaller than the baskets that they tamp, there can occasionally be areas of the sidewall that require this additional attention.
Once you are satisfied with your tamp, place the tamper on the coffee bed and briefly rotate it in one direction with no applied pressure. This is “polishing” the bed to smoothen it before extraction.
There may be loose grounds either sitting atop the coffee bed, or resting on the side of the basket wall. Quickly turn the portafilter upside down or brush it with your hand to remove the remaining loose particles.
Debunking the Tamping Pressure Myth
It has long been taught that variations in tamping pressure have an impact on extraction. While not totally wrong, this way of thinking is at least misleading. It is definitely true that a minimum force needs to be applied in order to achieve the proper hydraulic resistance to control flow. However, once that minimum force has been applied, greater force does not contribute to extraction quality or flow rate. Two factors account for this:
- Some or all of the pressure generated by tamping is immediately relieved when the coffee particles are wetted.
- The 50 lbs or so of force applied by a barista is nothing compared to the 500+ lbs of force applied by the pump during extraction.
The reason many baristas overestimate the impact of harder tamping on flow rate is understandable. When additional pressure is applied to the coffee bed, it becomes more compacted. When it becomes more compacted, there is more “head space” between the top of the coffee grounds and the dispersion screen. Because this space must be completely filled with water before the espresso machine will enact full pressure, the extra space results in extra time before the pump is activated and you can see the resulting extract from the portafilter. This extra lag time might lead a barista to overestimate the influence of tamping on flow rate.
Debunking the Side Tap Myth
For some time, baristas commonly made the argument that a tap on the side of the portafilter between tamps was necessary to knock down any loose coffee particles that were missed from the first tamp. Those particles would then be compressed with a second tamp. It’s not a bad line of reasoning, but it’s an improper solution to poor tamping. And the risk involved is certain not worth the reward of reincorporating a few loose particles.
When you use the tamper to tap the side of the portafilter, there is a good likelihood that you may break the seal formed between the coffee bed and the basket wall. If this happens, sidewall channeling will occur, ruining the shot. The second tamp does little – or nothing – to correct the broken seal.
But loose particles should not be a persistent problem if the correct tamping method is applied. Additionally, portafilter baskets have become much more exacting in recent years, reducing the amount of space available between the edge of the tamper and the wall of the basket.
