About the Smart-Tamp and Espresso Tamping
Creating delicious espresso requires freshly roasted beans, the right dose and grind distribution in the portafilter, specific tamping technique and tamping force, controlled water extraction pressure and temperature and dozens of other variables. Having instruments that are capable of measuring and recording these variables is key to understanding what goes into a perfect shot and being able to repeat it in the future. Tamping is a variable that is often overlooked, but if applied correctly, can fine tune your extractions as well as be able to lightly compensate for issues involving other variables like off-target doses or grind fineness issues. Let us explain.
Tamping technique and tamping force both control the compaction (density) of the ground coffee in the porta-filter. The density of the compacted coffee cake directly affects the resistance to water flow governing how optimally the water percolates through the coffee. A light tamp creates a less compacted—i.e. less dense—coffee cake in the portafilter making it easier for the water to flow through it. This is described as high permeability. Conversely, a harder tamp creates a denser coffee cake offering more resistance to water flow. This is described as low permeability. Permeability affects the flow rate of water through the coffee cake. The flow rate governs what volume of coffee is extracted into an espresso cup in a given time.
The equation which governs this behavior is shown below and is known as Darcy's law. Originally derived by a Nineteenth Century engineer named Henry Darcy, this equation relates flow rate to permeability, the area of the coffee cake exposed to water, the water’s viscosity, the pressure difference across the coffee cake and the height of the coffee cake.
The Smart-Tamp espresso tamper gives the barista the ability to measure the force, in real-time, that is applied to the coffee during the tamping process. This allows the barista to target or simply note the tamping force used on a shot of espresso. Furthermore, the Smart-Tamp allows the barista to compensate for adjustments that have been made to some of the other variables. For instance, if the grind turned out to be too fine from the grinder, then the barista has the opportunity to adjust for this by applying a lighter than normal tamping force—thus increasing the permeability of the coffee cake— and be able to record it and use it for future shots with that grind setting. On the other hand, if the grinder produced too coarse a grind then a harder tamp might be required to obtain the desired extraction. Similar tamping compensation techniques could be used to remedy doses that are slightly over or under dosed using the Smart-Tamp. Having the ability to nimbly adjust compaction with the real-time feedback of the Smart-Tamp allows you to control your extractions with high fidelity tamping adjustments.
The Smart-Tamp is always ready for use as long as it has the two working coin cell batteries inserted into the base compartment. Using the tamper is simple and intuitive: simply pick it up and gently shake it to wake it up, then tamp. A sensitive accelerometer senses the shake and boots the tamper up within a fraction of a second. In that fraction of a second the tamper tares (zeroes) to ensure an accurate reading of the tamping force during usage. When the tamper senses no activity it puts itself to sleep and consumes miniscule amounts of power.
The Smart-Tamps digital display comes in two variants, a kilogram scale (5-20 kg) and a pound scale (12-42 lbs), as shown below.
The Smart-Tamp is offered with two base profile options (flat bottom, curved bottom) and three base diameter sizes (53mm, 58mm, and 58.4mm). The curved base profile may offer better perimeter compaction in the coffee cake, which could help with reducing or eliminating water channeling around the perimeter. The curvature in the curved base is subtle and is illustrated in the sketch below. The 58.4mm diameter base is designed to fit VST baskets and some stock 58mm portafilter baskets.