San Marco blind filter for espresso coffee machines, code 3.026.069, for cleaning the group head/duct.

• Brand: San Marco
• Type: blind (holeless) filter for the portafilter
• Function: group head cleaning (backflush)

The blind filter is fitted into the portafilter in place of the normal perforated filter and, combined with a specific coffee machine detergent, allows backflushing: since water pressure cannot flow through the filter, it pushes the detergent back into the duct and the group head valve, removing built-up coffee oils and residue. It is typically performed in cycles (a few seconds of extraction followed by a pause, repeated several times) and should be done periodically to keep the duct and group clean, ensuring consistently good coffee quality.