Espresso can be a fine art to master with so many variables that can get in the way of a good brew. In this post we look into the difference between pressurised vs non-pressurised baskets (also known as single wall & dual wall filter baskets). There are both benefits and drawbacks to each style of basket which is important to understand when brewing espresso. Before looking at the differences between the styles of baskets it is important to have an understanding as to what purpose it serves.
Purpose of a Portafilter Basket
When looking at the anatomy of the portafilter, the basket is so named because it is a basket that holds your coffee grounds. These are able to be clicked in and out of the portafilter for cleaning, as well as changing of sizes.
Portafilters are designed with a mesh at the base. This is punched out of the metal to form a barrier with holes small enough that you will not allow coffee grounds to pass through it, while being large enough to let the water flow through. The mesh is designed thoroughly to ensure consistency between all of the shots that are pulled as well as to ensure an even extraction and flow of liquid through the coffee.
Pressurised Baskets (sometimes referred to as double wall baskets) consist of a standard mesh base followed by another 'wall' which has generally one small hole in which the extraction is forced through. This creates a greater level of pressure within the basket when brewing occurs. Commonly pressurised baskets can be found with most entry-level home espresso machines and may be provided with higher end home espresso machines. However they would not be used in a commercial setting.
So what are the benefits to a pressurised basket? The biggest benefit to using a pressurised basket is in the way it can greatly improve consistency, the pressurised basket will tolerate a less precisely ground coffee while still returning an acceptable extraction. This is particularly beneficial in domestic settings where a precise grind is not always available, or where the operator may just be looking for a simple setup without the hassle of learning the intricacies of espresso brewing. These baskets allow the use of pre-ground coffee while still producing crema.
The pressure that builds up behind the second wall helps to ensure that the water finds its way through all of the grounds in the basket and assists in drawing out the oils within the coffee. This is also the reason a less precise grind is also acceptable, people may be able to get away with using something more suited to a stove top or drip filter as the coffee is not necessarily creating the resistance, it's all up to the basket.
Non-pressurised baskets are the original style of basket used when brewing espresso. The difference here is that they do not contain the second wall, there is nothing else creating pressure when you brew your coffee other than the grind of the coffee and how hard you compress it when tamping. These are the preferred option for coffee enthusiasts, and what you will find professional barista using in coffee shops.
The reason that single wall filters are preferred by coffee professionals and enthusiasts is because they allow greater control of each extraction. It is very important to ensure you dial in your grinder correctly to find the best grind for your machine if using a non-pressurised basket. When using a non-pressurised basket, to achieve the best results you may need a finer grind of coffee, tamping also plays a much more important role in the extraction.
While these baskets do require more precision, your extra hard work will yield some great results. Non-pressurised baskets will give you a fuller-bodied extraction which exhibits all of the nice flavours we like in a good coffee (when you get the extraction right).
So if you have an espresso machine at home that has the ability to use a non-pressurised basket, give it a shot you may be surprised. If you have already tried it out and haven't had good results hopefully this post has provided a few tips you can use. If you would like to learn more about creating great espresso I have some links to some of our other posts that you may find useful below.
We would love to know about your experiences with pressurised & non-pressurised baskets in the comments below, otherwise we'd love to see you over at @guide2coffee!