Tamping of Espresso
Tamping locks in a distribution, polishes the surface of the coffee, and eliminates any large void spaces in the coffee bed. Tamping also offers a perceptive barista feedback about dose quantity, distribution, and grind.
How Hard to Tamp
Contrary to popular belief, the difference in flow resistance caused by lighter and harder tamping is minimal.” Once the coffee has been tamped with enough pressure to eliminate any large void spaces in the bed, additional tamping pressure will not have much effect on extraction quality or flow rate.-“” Two factors account for this.
1. Some or all of the pressure generated by tamping is immediately relieved when the coffee particles are wetted.
2. The 50 lb or so of force applied by a barista when tamping firmly is dwarfed by the 500+ lb of force applied by the pump during extraction.
Very firm tamping does not seem to offer any benefits, but there are at least two reasons to tamp lightly: it causes less stress on the barista’s wrist and shoulder, and it makes it easier for the barista to achieve a perfectly level tamp. (This is immedi ately clear when using a tamper and basket designed to have a very tight fit. When a barista tamps with a lot of force they will get stuck together much more frequently, indicating the tamper is not level.)
To Tap or Not to Tap?
A recent point of contention in the tamping debate is whether to tap the side of the portafilter between tamps. The argument in favor of tapping is that it dislodges any loose grounds which had crept up the walls of the basket during the first tamp, and those grounds can then be sealed into the coffee bed with a second tamp.
It is hard to see how incorporating a few loose grounds into the coffee bed is worth the potential harm done by tapping. The tap can break the seal between the grounds and the wall of the basket, creating an easily exploitable channel around the edges of the coffee bed. In my experience a broken seal is difficult, if not im possible, to fix with a second tamp. It might be possible to tap without breaking the seal, but tapping does not seem worth the risk. The bottom line: a few loose grounds are a minor problem, if in fact they are a problem at all. (I don’t think they are.) A broken seal between the grounds and the basket is a major problem.
One barista I admire taps with her wrist (an action akin to a strike with a “dead blow” hammer) in order to limit any jarring of the coffee bed. If you must tap, this seems to be a safer method than tapping with the hard handle of a tamper.
How to Tamp
Grip the tamper loosely in your hand, aligning the shaft of the tamper handle as if it were an extension of your forearm. Your wrist should be neutral, and the base of the tamper handle should sit comfortably in the hollow of your palm. This position will minimize strain on the wrist, which is critical for a barista who tamps hundreds or thousands of times per week.
Keeping the tamper level, squeeze it gently onto the grounds. That’s it. There is no need for a twist or a second tamp.
When you release the tamper some loose grounds might remain on the wall of the basket or on the surface of the coffee bed. Briefly turn the portafilter upside down if you wish to get rid of these grounds. Next, wipe the edges of the porta filter clear of grounds. Last, latch the portafilter onto the espresso machine gently in order to avoid jolting the grounds and breaking the seal between the coffee and the basket.
Perform the above actions quickly but carefully to prevent the portafilter from losing too much heat while it is unlatched from the group head.
Hold the tamper comfortably in the hollow of your palm with the saft of the tamper handle aligned as an extension of your forearm
The tamper should fit snugly into the portafilter basket. If the tamper is too small it will not seal the perimeter of the coffee bed, and channeling around the edges of the bed is more likely to occur. Ideally, the tamper should fit such that if it sits the least bit crooked, it will get stuck in the basket. I have had numerous tampers machined to fit my baskets and so far have found the ideal gap between the tamper and basket to be ‘i/1000 inch, i.e., a difference of 1(1/1000 inch (.25 mm) in diameter. A larger gap will create a slightly higher frequency of channeling over the course of many shots. Custom tampers can be made by a local machine shop or by a tamper manufac
turer willing to make custom sizes.
Whereas most commercial tampers are machined precisely, portafilter baskets can vary tremendously in size; in a recent batch of triple baskets I bought from one sup plier, the diameters varied within a range of 75/1000 inch, or 2 mm! I have found it is easy to find double baskets of consistent size and tampers designed properly to fit those baskets; I’ve had less luck with triple baskets. For triples my strategy has been to order dozens of baskets, measure their diameters to within 1/1000 inch, and return the baskets of exceptionally large or small diameter. Usually, the majority of basket diameters will be within a range of 2/ 1000 inch to 3/ 1000 inch; those are the ones I keep. Then I have a tamper machined to a diameter 1 0/ 1000 inch smaller than the smallest diameter in the range.
Please note: a standard 58-mm tamper designed for single and double baskets does not fit all baskets equally and is not designed for use with triple baskets.