This is another famous espresso style which many baristas try to emulate on their coffee machines.
It was made famous by the "slayer machine"
The Slayer is one of those holy grail machines.
This pic is of a single group version with a saturated group head.
What truly sets Slayer coffee machines apart from the rest is its patented Espresso two stage Needle Valve.
This was created to control the flow rate,.
This technology gives you the ability to adjust the water flow during the pre-infusion stage.
A slayer shot puts water slowly onto the puck (2mls/sec) for typically 25 - 40 secs.
(Its very different to a Londinium shot).
You can do this with any machine which allows you to control flow & pressure.
It uses very low initial pressure & flow during pre-infusion.
At the end of this time, the puck is fully saturated and the pressure will rise.
You only end the pre-infusion when you see the first drops of coffee at the bottom.
The nice thing about this is that it addresses solubility, esp for coffees like light roasts (where you need more contact time). The puck releases CO2 & gently expands in the basket. ... less chance of channeling.
Because prefusion takes so long, there will be a difference in water/coffee contact between the coffee at the top and the coffee at the bottom of the puck.
The coffee at the top might have ben in contact for 40 secs, while the coffee at the bottom only 1 sec.
This gradient between the top and bottom results on an uneven pre-infusion.
(The top might be over extracted, while the bottom is under extracted.)
This pre-infusion is followed with a full pressure extraction.
In summary:
2-bar pre-infusion (for 20-40 seconds) and then move to full pressure extraction for another 12-13 seconds
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