A dual wall, in the context provided, refers to a type of pressurized espresso filter basket.
Understanding Dual Wall Espresso Baskets
Specifically within the realm of espresso machines, a "dual wall" basket is a design feature of the filter basket used to hold coffee grounds. Unlike standard single-wall baskets that have numerous fine holes across the bottom, dual wall baskets typically have a porous inner wall and a single, small hole (or a few very small holes) on the outer wall.
How Dual Wall Baskets Work
This design creates artificial pressure as the hot water is forced through the coffee puck and out the small exit hole(s). This added pressure helps to compensate for inconsistencies in grind size or tamping, which can be particularly challenging with pre-ground coffee.
The provided reference notes that these baskets are:
- Primarily used for pre-ground coffee: They are often included with entry-level or semi-automatic espresso machines and are recommended when not grinding coffee fresh or using a non-espresso specific grinder.
- Can help extract a good shot of espresso: The pressure they build assists in achieving a crema and body that might otherwise be difficult with pre-ground or improperly prepared coffee.
Benefits and Drawbacks
Dual wall baskets offer ease of use and forgiveness, making it simpler for beginners or those using pre-ground coffee to get a decent result. However, they offer less control over the extraction process compared to single-wall baskets, which are preferred by enthusiasts who grind fresh and focus on dialing in their grind size, dose, and tamp for optimal flavor.
In summary, a dual wall (or pressurized) basket is a specialized espresso filter designed to simplify the brewing process and improve results when using pre-ground coffee by creating artificial pressure.
