A doser is a mechanism, usually attached to the front of a burr grinderA coffee grinder that grinds by passing a flow of beans between a pair of rotating metal discs.: A coffee grinder that grinds by passing a flow of..., for putting coffee into an espressoA small coffee beverage, about 20 ml, prepared on an espresso machine where pressurized hot water extracted through compressed coffee.: In its most stripped-down, basic form, this is... portafilterThe part of an espresso machine which holds the filter basket, into which coffee grounds are placed.: The part of an espresso machine which holds the filter basket,... basket.: A doser is a mechanism, usually attached to the front of a burr grinder, for putting coffee into an espresso portafilter basket. Ground coffee sits in the doser and is pushed out and into the portafilter by the pull of a lever. Dosers are designed to push out the same amount of coffee (typically 6-7 grams) every time the lever is pulled, but, in practice, this feature only works is the doser if full of grounds, which is unlikely to happen in the case of a home user.