Why is this important? Gaggia machines are shipped adjusted to 11 bar from the factory to accommodate ESE pod standards. Pods are very popular in Europe so being certified as a good pod brewing espresso machine is important to the manufacturer. Non ESE pod espresso - ground coffee espresso - tastes better at 9 bar of pressure than it does at 11 bar. The grind can be coarser, the doses can be smaller, and the extraction is correct as well. Better tasting espresso is what it is all about and this simple tweak gives this to the Gaggia. Can you make a shot with out performing this adjustment? Sure you can, it is just harder to get a great shot since the margin for error is small at 11 bar compared to 9 bar.
How do you make the adjustment? Unplug the machine. Remove two screws from plastic on top toward the back. Remove the top cover. Locate OPV - it will be a brass tube attached to the bottom of the boiler with a line coming in from the pump and another line coming out of the top that runs down into the water tank. Take off the tube from the top of the brass OPV, then remove the threaded cap with a 17mm or adjustable wrench. A little water will be sitting underneath - this is normal. Take a 5mm Allen wrench and turn counter clock wise 240 degrees (not quite 3/4 of a round). Replace 17mm cap. replace water line to OPV. If everything is tight you shouldn't have any leaks. Replace cover and screws. Plug in, let it heat up, and pull the best shot the Gaggia Classic can make.
Some Deep Cello Black Tie Blend before I go.
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