Kens Espresso Fueled Ramblings

On most high end espresso machines you have something called an over pressure valve.

The function of the over pressure valve is to release water back into the water tank when the pressure in the system rises above a set point.

When you brew a shot, watch the pressure gauge, it should hoover around 9.5 bar on most machines.

I like my over pressure valve to be slightly to high, around 11 bar. This is because the higher pressure keeps me on my toes.  See, if the over pressure valve was set to maintain 9-9.5 then I would never know if my grind was to fine except when I totally choked the machine. But with a higher pressure of 11 bar, now I have to adjust my grind or the shot will flow to fast. I can now also use the pressure gauge to see if my grind is on, when it is the puck will be the thing that maintains 9-9.5 bar, if I have to fine a grind the pressure gauge will tell me because it CAN go over the ideal 9-9.5 bar.

A slightly high pressure is all good as long as you only pull doubles (As I do), it doesn’t work if you pull ristrettos (Pressure goes to high) or singles (Pressure does not get enough resistance from the puck mass) It also only works on vibe pump machines, rotary pumps have a much higher throughput so the force is to high even for doubles.

If you have an overpressure valve, experiment by all means by going a little bit low or high, taste your shot as you might like it. High pressure tends to make the coffee a bit more sharp and bitter, lower pressure more crema and sweetness but also more acidity.