Abstract: The present invention refers to systems and process associated with beverage preparation based upon the extraction of a single portion (1) of a pre-measured quantity of precursor substance in a brewing apparatus (4), whereby said single portion (1) presents a compostable confinement (2) and can be collected inside of a portion holder (3) that is adapted so that can be retained inside a cavity of said brewing apparatus (4). In particular, the present invention relates addresses the problem of ensuring effective and reliable retention of the portion holder (3) on the brewing apparatus (4).