Best of American Beer and Food

How Pressurised Filter Baskets Work

Pressurised filter baskets rather disappointingly appear to be taking over the espresso machine market. Gaggia now ship them as standard; Ascaso put them on their ‘Versatile’ machines; not to mention all the small domestic appliance manufacturers who dabble in a bit of everything, including espresso machines. The worse thing is that often these manufacturers ‘pretend’ that these filters are in someway better than the standard ones. The same standard filters which are used by professionals in every (well I hope every) coffee shop throughout this land.

Gaggia state that:

“…thanks to our constant efforts towards product improvement…The (standard) ground coffee filters and the pod filters have been replaced by the new “Crema Perfetta” (pressurised) filters, which improve the final beverage by producing an even thicker crema, typical of espresso coffee.”

You can see why some manufacturers opt for pressurised filters. To make good coffee on an espresso machine takes a lot of practice and patience. Pressurised filters are essentially a cheat as they pretty much guarantee that no matter what you do preparing your espresso, the resulting drink will look like an espresso (i.e. will have a crema). Look being the operative word. What it tastes like is creamier and less flavoursome than a true espresso. The nearest thing I can think of to compare it to (and this is only going to relate to a small niche) is the difference between a proper hand-pulled pint of ale and a nitrogen assisted smooth/cream flow pint.

How True Espresso is Brewed

Before I explain how pressurised filters work, first I’ll explain how true espresso is brewed using standard filters. The key to brewing quickly, like for espresso, is to brew using pressure. Pressure energises water to extract flavour more quickly from the coffee grounds.

For an espresso you need to brew under somewhere between 7-9 bar. Under this amount of pressure it’s possible to extract all the desirable flavours from the coffee grounds in 20-30 seconds. For this reason espresso machines are fitted with a pump. Whilst the pump is responsible for producing pressure, it will only generate enough force to push water down through the group head. As water on its own offers little resistance to the pump (gravity is already acting on it), little pressure is generated.

This is where the all important cake of ground coffee in your filter comes into play. It’s the cake’s responsibility to act as a barrier to the oncoming flow of water so the pump has to work much harder. This is why we grind fine and tamp down, so the cake can provide resistance till, finally, after around 8 bar of pressure has built up behind it, water penetrates the cake extracting all those lovely flavours.

How Pressurised Filters Work

When brewing espresso with a pressurised filter, there is no longer a reliance on the coffee cake to form a resistance to the pump. This is because the filters are designed to add pressure once the water has passed through the coffee cake and formed a coffee solution. Typically these filters work by bottlenecking the solution by squeezing it through one tiny hole and it’s this that causes a crema to form and so look like an espresso.

With pressurised filters, there’s no need to tamp, or grind fine. You can even use stale coffee.

The problem is that adding pressure after the brewing process, rather than during, doesn’t help the extraction process. It’s too late. It doesn’t energise the water to extract more from the coffee cake. So if your coffee cake doesn’t form an effective barrier to the pump, then even though the resulting brew will look like an espresso, it will lack flavour as there will be plenty of desirable flavours still locked away in the cake.

Even if your coffee cake does form an effective barrier, because the resulting solution is then subjected to further pressure this messes with the makeup of the drink. The texture is creamier and the delicate flavours are destroyed.…