<P> Espresso is made by forcing very hot water under high pressure through finely ground, compacted coffee . Tamping down the coffee promotes the water's even penetration of the grounds . This process produces an almost syrupy beverage by extracting both solid and dissolved components . The crema is produced by emulsifying the oils in the ground coffee into a colloid, which does not occur in other brewing methods . There is no universal standard defining the process of extracting espresso, but there are several published definitions which attempt to place constraints on the amount and type of ground coffee used, the temperature and pressure of the water, and the rate of extraction . Generally, one uses an espresso machine to make espresso . The act of producing a shot of espresso is often termed "pulling" a shot, originating from lever espresso machines, which require pulling down a handle attached to a spring - loaded piston, forcing hot water through the coffee at high pressure . Today, however, it is more common for the pressure to be generated by an electric pump . </P> <P> The technical parameters outlined by the Italian Espresso National Institute for making a "certified Italian espresso" are: </P> <Table> <Tr> <Th> Parameter </Th> <Th> Value </Th> </Tr> <Tr> <Td> Portion of ground coffee </Td> <Td> 7 ± 0.5 g (0.25 ± 0.02 oz) </Td> </Tr> <Tr> <Td> Exit temperature of water from unit </Td> <Td> 88 ± 2 ° C (190 ± 4 ° F) </Td> </Tr> <Tr> <Td> Temperature in cup </Td> <Td> 67 ± 3 ° C (153 ± 5 ° F) </Td> </Tr> <Tr> <Td> Entry water pressure </Td> <Td> 9 ± 1 bar (131 ± 15 psi) </Td> </Tr> <Tr> <Td> Percolation time </Td> <Td> 25 ± 5 seconds </Td> </Tr> <Tr> <Td> Volume in cup (including crema) </Td> <Td> 25 ± 2.5 ml (0.85 ± 0.08 US fl oz) </Td> </Tr> </Table> <Tr> <Th> Parameter </Th> <Th> Value </Th> </Tr>

How many mls is a shot of espresso