EM 2.02 Line Pressure and the Snider Machine

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In most towns, the public water supply is pumped out of a large reservoir or an aquifer (an underground water deposit), purified, and then pushed up to an elevated holding tank, usually sited at a high point in the terrain. This allows the water to syphon downward into houses and businesses via gravity. The water usually arrives at a café with between 1 and 6 bars of ‘line pressure’, depending on the elevation of the water tank — the higher the tank, the greater the pressure. Every 10 metres of elevation produces an additional 1 bar of line pressure.

A model of how water line pressure varies, depending on the location of your cafe 

Where elevations are excessive, water suppliers add pressure-reducing valves to the water mains. Around 3 bars of line pressure is generally considered optimum for espresso machines. 

 

An Experiment with Crema

Espresso crema is widely believed to have been seen for the first time in the 1940s, after the invention of the Gaggia lever machine. But we at Barista Hustle think it’s more likely that crema became central to the marketing of espresso after this time. To find out whether espresso crema might have been seen a little earlier than the ’40s, we designed an experiment with the help of Argentine barista trainer, Julia Parera Deniz. 

 

Observations

There was one goal in this experiment: Do you get crema when you brew at 3 bars? The answer is, you certainly do. 

We used three simple metrics: shot times, thickness, and persistency. 

To test the thickness, we poured the espresso into shot glasses and measured the thickness of the crema with a ruler. As you can see in the results below, the machine produces a thick layer of crema at 9 and 6 bars. The shots pulled at 3 bars still produced a thick layer of crema,

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