After nine bars, pressure begins to compact the cake and water struggles to trickle through. As such, maintaining pressure at nine bars produces a sweet, pleasant espresso that holds its richness and deep flavour, containing enough water to prevent bitterness and enough caffeine to satisfy the consumer.

The BAR measurement (known as barometric pressure) is essentially the number of atmospheres of pressure exerted upon coffee grounds. A BAR of 9, for example, indicates that the pressure of the water being pushed through the coffee grounds is 9 times that of Earth's standard atmospheric pressure of 1 BAR.

Nine bars is considered ideal for high-quality espresso, though you can also get solid extractions from seven or eight bars. If you're thinking of using more bars than that, reconsider! It's all about balance in the world of espresso, meaning too many bars can be just as damaging as not enough.

Again, the ideal pressure for an espresso shot is 9-bar, which produces a perfect balance of flavor and extraction. Too much more than 9-bar can result in a burnt-tasting espresso, while too less than 9-bar will produce a weak and overly bright shot.