- Hi. Ryan from Prima Coffee here, and behind me is the coveted
Slayer Single Group Espresso Machine. Today we're gonna
discuss one of it's most important concepts, and that is, pressure versus
flow. So, in terms of it's extraction process, Slayer's approach is really
unique. Instead of offering direct control over pressure during the course of a brew
cycle, Slayer's internal gear pump actually operates at full pressure during
both it's pre-infusion and full infusion stages. Now a secret to this can be found
here under the hood.
So in my hand here is the adjustment knob for what's called a needle valve. A needle
valve allows precise regulation of flow, through the adjustment of a threaded
needle-like shaft that works to create restriction and moderate pressure. Now
here's an example of a needle valve. This is very different from the one that's
found in the Slayer, but we were actually able to cut this in half to give you an
idea of the mechanics. So as you can see, that center shaft moves either up or down,
to either increase or decrease flow restriction. So, what is the relationship
between pressure and flow? Well, to put it simply, pressure is the continuous
application of physical force. In this case, the pump. Flow being the actual
movement of water. Now the initial pressure that reaches the coffee varies
based on the amount of restriction created for the water prior to it entering the
brew chamber. In this case, the majority of the initial pressure created by the
pump is applied at the needle valve. And it's the minimized flow through the
very small orifice of Slayer's valve that slowly fills the brew chamber,
resulting in a low-pressure introduction of water to puck.
So I've got a back flush disc in here, and what we're gonna do is allow the
machine to run in it's pre-infusion stage, and we're gonna watch the pressure gauge.
So even though the pump is currently
operating at nine bars, you can see that the pressure is very slowly raising.
Now, as I allow this machine to run in
it's pre-infusion stage, long enough for the water to fill the brew chamber. You'll
notice that the pressure will actually eventually get up
to nine bars and equalize.
So to help give you a better understanding of how flow restriction
works to moderate pressure, our local fire department is here to
help with a quick demonstration.
So here we have two hoses, both operation under the same pressure,
but each has a different size nozzle. We're gonna find out if these fill their
barrel at different rates. Ready guys? Go.
All right. That's it. So even though these hoses were technically operating under the
same pressure, the barrel under the wider hose filled first. This is exactly what
Slayer's gauge told us about the pressure inside it's brew chamber during
pre-infusion. The pressure applied to the inside of this barrel increases slowly, as
a result of the decreased flow rate, caused by additional restriction in the
water line. So what is the difference between a Slayer and a pressure-profiling
machine anyway? So, most machines will kick on at full pressure. Extraction will
last about 25 to 30 seconds. Some machines offer variable pressure, but
typically begin with water lining pressure, and pre-infusion then, will last
about 5 to 7 seconds. Now, Slayer is not a pressure-profiling machine. But instead,
allows three stages of flow, which are centered around the ability to enhance and
extend the pre-infusion process, as desired. Now, I also think it's worth
noting that both Slayer and pressure-profiling machines approach
flavor-profiling through the same basic median, and that is variable flow, or in
more familiar terms, agitation. Variability of flow in Slayer's
pre-infusion stage is the machine's most defining attribute, and it has some major
implications. So why is this important? Well, first we find that the gentle
introduction of water results in a full, more even saturation of the puck.
Decreased water flow, consequently, works to minimize the initial introduction of
pressure, creating a soft, ramping effect, which we saw, which aids in saturation,
and allows us to extend pre-infusion anywhere from 15 to 30 seconds, as
desired. With complete saturation come greatly improved water flow through the
puck, and the ability to grind substantially finer, which will increase
the body of espresso. Advanced brewing concepts teach us that the process of
extraction is non-linear, meaning that, through controlled manipulation of brewing
factors like agitation, specific flavor characteristics can actually be targeted
and accentuated along the way. And it's the combination of Slayer's variable flow
and three-stage brew process that give it an enormous amount of versatility, in
terms of flavor profiling. So I hop that lends some understanding to the inner
workings of this machine, and what it is that makes the Slayer so unique.
Thanks for watching.