To make perfect espresso, the water pressure needs to be very close to 9 bar for perfect extraction of coffee aromas. Unfortunately, most espresso machines are supplied from the factory set to above 10-11 bar, resulting in insufficient extraction of the essential coffee oils, and leaving thin tasting coffee lacking in well rounded, robust coffee flavours. The water flow is too rapid, and cracking of the compressed coffee puck means that a proportion of the ground coffee is bypassed further limiting the extraction of flavour. Users often misdiagnose the problem, and move to a coarser grind which in fact exacerbates the problem, or in extreme cases replacing the coffee maker in the hope of improvement. The key to solving the problem is to accurately measure the water pressure at the portafilter to allow adjustment to meet the the critical 9 bar pressure. Many coffee machines have an adjustable over pressure valve (OPV) on the output of the water pump, or on the side of the boiler.