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Roaster School Online – #16 – Revisiting the discussion on airflow

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Roaster School Online – #16 – Revisiting the discussion on airflow


… this morning on the new espresso machine it was greatOh heyWhat’s up!Oh hey, we’re live. Hey, this is Joe MoroccoI’m Eliza Lovettand we are here at Mill City Roasters to bring you some more coffee education todaywelcome.Welcome. We were just talking about some weird roast curves and how how to kind of trick out
a coffee that may be outside of the bounds of what normal coffee is. A lot of
times when we’re just roasting those “washed mild coffees,” as we’ve been
learning they’re called, they may may roast in a very set way, but when you
get a big Pacamara that’s a natural, you may have to change things up a little bit.Yeah, or those wacky honey process. Lots of fun.So today we’re going to talk to you about air again and how we use airflow and a roaster, and how we can, I guess, go a little deeper into airflow so
that we can get more out of our coffee. So today Eliza is going to be helping me
out, keeping me from going into the weeds too far and asking
questions that maybe I’m not anticipating too much. So again,
if you’re at home, feel free to ask your own questions in the chat and
we’ll hopefully get to those, but we had some discussion around airflow and it
has since sparked a lot of questions coming to us about air flow that may be
in our first airflow video we didn’t get too in-depth on, so we want to clear
that out and see if we can reset on air flow. Do you have any initial questions
for us today or should I just dive right in?Well, I’ll start with the question that I get asked all the time.Ok.I’m going to go right for it.Go for it.Yeah, why do we use airflow? Why do we moderate the changes? Why do we do this?That’s a very good question. So
as I began to roast coffee I was taught that air flow was a heat application
source. We know that it’s a resource for heat.We know that convection is a more
economical way of heating – it actually will heat coffee much more quickly than
conductive heating will, conductive being that heat of touch, the transfer of
heat from when one thing that is hot touches something that is cooler. Well,
this is air that is hot touching the coffee that is cooler as the air moves
through the drum, usually off of the burner set. I was also taught that we are
not supposed to touch that. That we just allow that air flow to kind of roll
through and this is more of an old-school way of thinking about heating
coffee. A lot of your older roasters don’t really have air flow control, or if
they do have air flow control, it’s in some kind of set point, like one, two set
point, you know, where you have it 50 percent and a set point where you have
it totally off. And I wanted to talk about that for a minute. So, if you have
your vent pipe and that vent pipe – sorry – this is a vent pipe, and the air is
moving through this pipe, right? And you have a damper, and that damper is made to
kind of flip up and down. So as you move the damper in one direction or the other
direction, it’s going to tighten around the pipe. So then that means that the air now has to go around that damper in order to
continue out of the pipe. Well, a lot of times we think about – oh, thank you. Nick
with the save – a lot of times – I love pink – a lot of times we think about when
we have this set at a hundred percent, which is what we think of as being fully
open, that air is moving through it a hundred percent. That would be correct.
But we think that then when we set it to 50%, that that air is now moving
at 50%, and that’s really not correct, because what air likes to do is
maintain speed and just tighten. So the air will just tighten as it goes through
this space and as it tightens, it just goes around real quickly
may slow down a little bit, but that’s not really a big enough adjustment to
make an impact in the drum. We’re not really stifling airflow until we get
quite a bit closed, and then that airflow starts to kind of have, like, back
pressure, back into the drum. That’s when we start seeing our airflow slowed down,
and on a regular damper system there’s really no way to tell whether or not
that is at 50% or if it’s at 25%.There’s really no way to tell. So
that’s why on the machines here at Mill City, instead of it being a damper system –
and a lot of other roaster manufacturers are kind of moving toward this kind of a
system – the fan itself, which is usually a fan that has, like,
blades that go this way and the fan is moving like this, so it’s pulling air
through the system. We can slow that fan down or speed that fan up. You’ll hear me
talk about 100% airflow, 50% airflow, 25%, you know, throw out these random
percentages, and that is, if you have a dial which – on the North machine, I’ll
just use that as an example – you’ll have a dial that kind of goes from zero to a
100, and then 100 is what we think of as 100%, but in any given
roast it may be the case that 70 is gonna be the fastest that your air flow
will go and thirty may be the slowest that your air flow may go. Which, I
know, that’s not exactly 70/30, but as you turn that dial your fan speed goes
faster and faster and you’re able to pull more air through that system or
less air through that system. And that measurement is actually real, so whenever
I say “for this roast you should go to 100% air flow at this certain time,” 100%
would be the marker 70 for that. So that would be – equals – 100% for that
particular roast. And then whenever I say 0%, that would equal 30 for that particular roast.Because if you go below this on
the North machine, you’re not going to pull enough oxygen into your burner area
so that your burners will stay lit. Your burners will – your fire will start
drifting off of the burners and they’ll start using the air that’s coming into
the panel as their source of oxygen. So you’ll start seeing this drift and
that’s not a very safe thing. So you want to keep air flow moving enough to where
you’re still feeding that flame and keeping the flame set. And also another
really good thing to keep in mind that that Steve reminded me about today as I
was speaking about this is, if you turn your air flow completely off- if it’s at
zero – then at zero, you are now issuing a lot of gas and NOx fumes into the system,
and that’s gonna push its way into the coffee itself. It’s going to push its way
into that or it can push its way into your drum, which is very unhealthy thing,
can be a very unhealthy thing, and then if you have your burner – let’s pretend
this is a roaster here – and this is your burner under here, so, in
your burner box, if this air starts, you know, getting gas that it cannot catch
flame and that gas starts moving into your drum, and then all of a sudden you
do open up your airflow and pull air through, now all of a sudden that oxygen
can hit that fuel and you might have a burst of flame in your drum itself. So
you want to be very careful in the beginning of your roast that you don’t
go too low on airflow because if you go too low, you can cause a lot of other
issues. So when I say 0%, know that I’m talking about 0% for a particular roast. Does that make sense?Totally! Now … here’s a real question though.Ok.What about this 100%?So this is a great lead-up question.Can there be too much air, perhaps?There can. So this is something that when
Rob Hoos was here a couple weeks ago he was talking about , and it left a lot of
people with some questions that I’m gonna revisit – not to put words in his
mouth or say he’s right or wrong or anything – but just to further explain
what his explanation was. So a lot of roasters have been engineered – and
especially your more historical roasters – to where when you are at a full open
airflow or what we would call 100% for the machine, that at that point you are
bringing in maximum energy from your flame. So here you have your flames
they’re burning.This burner box, the set of flames has a certain number of BTUs
that it can maximize, that it can reach as a maximum level. So let’s just pretend
this number is 10,000 BTUs. Okay, so if this flame can create 10,000 BTUs, then I
can correlate a fan that at 100% speed or whatever the power of that particular
engine is, that fan will pull 10,000 BTUs off of the burners and into the drum.
Okay, so now if that fan were to go higher than that – let’s say the fan were
to move capacity beyond what 10,000 BTUs can heat. So let’s say if there’s a
certain number of cubic feet of air, cubic feet of air – that’s what this is
gonna be. Let’s say that like 150 cubic feet of air being pulled across this
burner in any minute. So this is hypothetical that 10,000 BTUs can heat
this to 500 degrees efficiently.But now, all of a sudden I
have a fan that can pull more than 150 cubic feet of air through that space. So
if my fan is more powerful than what this burner has the capacity to heat in
the amount of time that it takes to pull that air through, now all of a sudden if
I can turn my fan up higher and higher and higher – let’s say turn it up
to 11, if we could turn it up to 11- then all of a sudden this 10,000 BTUs is
not enough to heat it to 500 degrees. So what if I have a fan that is able to go
up to 300 cubic feet per minute. Now, instead of having the capacity to heat
to 500 degrees, I might only have the capacity to heat to 300 degrees. Well, 300
degrees is cooler than where I want my coffee to go, so what Rob was talking
about – I’m gonna lose the roaster – I know this is beautiful – I’m sorry – I’ll lose
the roaster for a minute – so what Rob is talking about is if you have a fan that
is super efficient at pulling in air and a system that’s super efficient to
pulling in that air through, that ability to heat is a bell curve, so as
your fan is low you’re not pulling in energy through convection, or maybe very
little energy. As you turn your fan up, you’re pulling in more and more energy
off of your burner. And then as you turn your fan up more and more,
now all of a sudden you’re pulling so much air in that your burner doesn’t have the
ability to stay caught up with the amount of airflow. So on a on a North
machine, we certainly have a very very high efficiency fan, and so you’re able
to find this kind of a bell curve that exists. What a lot of your more
traditional roaster manufacturers did was they only put in a fan that was
maxed out, so you cannot use the fan to pull in cool air, which I kind of like because you can use it as a brake system.YeahYou can pump a little cold air if you want to slow the coffee down, whereas this you have to
pull off of the air but that doesn’t necessarily cool the system down. You
have to wait for then the metal to cool itself down because now you have less
movement through the system and that metal will hold on to heat even more so
you can’t use it as a brake system. So, for a North machine you can use air flow
as a brake system because you have the full gamut of not pulling in energy to
pulling in weight way more air than the burner is able to keep up with, because
that air is just pumping through very quickly into your system. If you think
about air moving from the outside of a of a drum to the inside of a drum in a
matter of a couple of seconds there’s no way that that fan is our that flame is
going to be able to heat that air appropriately for that space so
furthermore that means that hypothetically there could be a setting
on your airflow where you are maybe not bringing in maximum efficiency of air
and temperature but you’re in a place to where in the beginning of your roast
you’re not stifling energy too much but then in
your at the end of your roast you’re still allowing for enough energy to
where hypothetically you could find one air setting for an entire roast so
that’s what Rob is meaning whenever he says that he doesn’t adjust air flow a
lot on a regular drum roaster obviously if he’s roasting on a lowering he’s
adjusting it all the time because it’s set with the gas but on a regular
roaster he does not worry about this too much so when you think about adjusting
air flow I want you to think about it in terms of whether you’re converting over
to convective energy or sticking with conductive energy as the energy source
that you’re using to heat your coffee we prefer oh yeah go ahead no question that I get a lot in class
okay well if we’re using mostly convection in this roast why are we
starting with the airflow so low yeah so if you are using low airflow in a roast
by nature of using low airflow your your energy that is going to be moving from
your system to the coffee that heat that the coffee is absorbing is going to be
coming through the metal of the drum more than it’s coming from the air
because the air is not moving that much it’s it’s a good question so this is
what we talked about in in the first episode that we talked
about air flow I want to say maybe two years ago actually so what what you have
is the seed that is you know 12% moisture in the beginning of your roast
by affecting it with energy that is that is low efficiency the seed is able to
absorb that energy in a slower manner to where the the evaporative process is not
moving as quickly and so the moisture that is in this coffee is able to then
pull that energy into the core of the seed much more slowly and efficiently
and for a really dense coffee that wants to pull energy and very quickly it’s
also wanting to expel h2o very quickly that’s wanting to pull out and so what
happens when that pulls out is you’ll get a layer around the outside of the
coffee that is more dry than the core this dry layer then acts as an insular
layer that prevents energy from moving through as efficiently but then once
energy is in now the h2o that is here that’s horrible
the h2o that is here is under pressure and so now it’s not able to move out as
efficiently as it would have if we would have moved energy more slowly in so if
we move energy more slowly in basically what happens is energy moves in moisture
moves out in a nice slow fashion it’s kind of like if you’re in a crowded bar
and somebody yells fire and there’s only one exit and everybody in the bar has to
exit out of that one place all of a sudden you have a traffic jam a lot of
pressure things get hurt that’s what happens in coffee but if you leave the
building in a nice orderly fashion then everybody can move out of the building
safely and you have affected the change that you want to in that system so we
need low efficiency heat and conduction is a lower efficiency heat however
that’s not to say that there’s no convection in the beginning of the roast
or that there’s no conduction in the end of the roast both of these heat transfer
methods still exist throughout the entire experience of roasting however
we’re leaning into conduction in the beginning of the roast by slowing our
air flow and we’re leaning into convection later in the roast well why
do we want to do that well once we have gotten rid of a lot of the water or at
least set up a system to where this water can now more easily and more
smoothly evacuate the the seed now we can hit it with efficient heat and that
efficient heat is needed to create mired reaction and caramelization if we hold
h2o in the coffee then mired reaction can’t happen
caramelization can’t happen if caramelization is trying to happen that
h2o molecule will start trying to break off of your carbohydrate molecule which
that’s caramelization on a molecular level but then it’ll meet other h2o and
so it’s not as efficient at breaking off and so that molecule instead of breaking
off the h2o might break off another
segment of the molecule like a carbon dioxide segment or something like that
and instead of you getting a simplified sugar you might get another molecule
that is tasteless to us or that you know tastes bad so does that make sense
cool so again revisiting this in terms of for those of you that are
specifically on a North Machine what what we talk a lot about on roasting on
the north is on that dial that you have that starts at zero and ends at 100
between the 70 and the 30 mark this range is really kind of where you want
to be for most of your air adjustment if you’re going into this segment here
you’re probably bringing in too much cold air you can use this as a brake
system to slow your roast down if your row starts getting out of hand to go
into this segment here you’re probably not bringing in enough air this is at
near zero or your fan may even turn off and in reality it if you have the drum
completely devoid of coffee then you’ll see that your fan in this range is still
spinning and still moving air through the system however when you add coffee
into that system now you’re stifling the airflow through
the system so now the fan needs to be ramped up to that thirty number which is
arbitrary to rpms but just think about it in terms of the number on the dial
that needs to be ramped up in order to have the force to still pull air through
that system so this is kind of your happy place where you want to live any
thoughts on that how do you approach that as my own reactions once I start seeing
yellow that’s when I start increasing air okay I’ve heard some different
thoughts on that and I’ve also heard you know there are people who will max out
around first crack and then bring it back or they will again like go a little
bit over that hundred percent to pump the brakes if you will uh-huh and then
bring it back when the coffee becomes so draw a line here there are a lot of
theories on this and in all reality none of these theories is wrong or right it
could be the case that a particular coffee reacts better to one of these
theories and another coffee may react worse to one of these theories so it’s
important to kind of keep your options open but in general my approach is low
air flow until I start seeing browning reaction and then I go to whatever my
100% is for that particular roast so in general on our north I would start at 30
and then once I see browning I would go to 70 immediately those would be my only
adjustments that I would make during the entire roast you want to make sure also
across the board that your airflow is either off or very low when you drop
coffee into the roaster because that air can pull beans back you know generally
as you drop it through the hopper it’s gonna it’s going to cross the air that’s
flowing out so if you have your fan really high when you’re dropping coffee
when you’re charging your roast that will suck some green beans back into
your chaff can which is a waste so we don’t want to do that but generally I’ll
be at 30 when I start the roast and I’ll be at 70 when I end the roast now on a
on a pro bot I will be probably at zero when I start the roast and I’ll be at a
hundred percent by the time I start seeing browning reactions if I am
roasting a coffee that is really dense and really moist
then I will probably stage up my airflow as that coffee is roasting if I have a
coffee that is really low density and not very moist at all I may not go down
to 30 I may be at a higher efficiency heating much earlier because I know that
I need to push energy into that coffee and I don’t have to worry about moisture
in that coffee as much so so I would probably approach it with pretty high
efficiency heating so I would want to really pump in some energy into that
coffee through the airflow and I probably do that a little bit more up
front and then I might relax that coffee as it’s going through the my yard
reaction give it some space and time to really go through development of flavor
and then I might allow it to kind of speed up as we’re getting close to the
end of the roast yes if you if you have energy that is
springing into the coffee very quickly which density this is a this is a actual
rule of physics higher density equals faster transfer that’s right lower equals slower so if you have metal energy will move
through metal very quickly if you have water energy will move through it kind
of quickly if you have air energy moves through it very slowly if you have space
energy doesn’t move through it except for in the form of light waves or some
what is I’m trying to think of the third kind of heating sorry my infrared yes
infrared energy will move through space but you won’t have heat transfer heat
transfer through any kind of material so the more dense your material is the
faster your heat transfer the lower your density is the slower that heat transfer
so if I have a low density coffee I need to compensate for the slower amount of
energy are the slower movement of energy by being more efficient on that
however conversely I need to compensate for the high and fast transfer of heat
on a dense coffee by slowing that process down yeah so think about your
your damper as how you would monitor your heat transfer think about density
and density you know a lot of people think about density corresponding with
moisture but again these two things are different if a coffee has more moisture
it will be more dense but that doesn’t necessarily mean that a coffee reading
more moisture is more dense you could have a very high moisture low dense
coffee so think about how moisture content in the coffee correlates to
density in the coffee and then how you want to represent that coffee on the
table and then use your heat transfer methods of your damper or your fan speed
and we like fan speed because it’s a lot more accurate to measure and to control
and to repeat do we have any questions coming in so the question is how does the increase
of air flow affect the rate of rise well that is going to depend if you have air
flow that at maximum is also maximizing your Heat then the more you increase
your air flow the more you increase your rate of rise if you have air flow that
will eventually decrease the amount of heat that you bring in so on the other
end of that bell curve then you will see your rate of rise increase as you
increase air but then it will start decreasing as you increase air further
because now you’re pulling in too much cold air so you can’t you have to really
know your system the particulars of your system to see that reaction so when
conducting any kind of experiment you want to set up all of your parameters to
be the exact same except for the one thing that you’re changing so I
recommend if you want to know on your system use the same coffee use the same
gas setting don’t change the gas setting at all throughout the roast and then
increase your air at different speeds and see which one causes a higher or a
lower rate of rise then you can answer your question on your system yes so on so there’s a question where do
we find the 30 and 70 on the Mill City roaster it will actually say 30 and will
actually say 70 on a different dial it may be a totally different way of
reading it there may be a magnet hillock way of reading it to where you may have
and you may have a dial but then you may also have a box that is measuring the
amount of electricity that is going through and so it may be a different
setting to where this is you know showing one number here and then as you
increase your air flow it may move the needle to another area so that’s why on
your system you need to figure out where you’re 100 percent for a full batch of
coffee is where you’re 100 percent for a half batch of coffee is and kind of go
from there every system is just so different
ooh so this question is how does air flow influence flavors well that is the
question every coffee has its own set of potential flavors that you the roaster
have to worry about unlocking air flow and changing air flow is going to change
the way that you unlock those flavors for that particular coffee in your
particular system so what I do on a North machine – a natural pocket Mara
may be different than what you might do on a lowering for a natural pocket Mara
for instance so the way that we manipulate air flow through a system is
going to vary depending on that system so it may be the case that we do very
different things with air flow on very different machines for the same coffee
and get a very similar taste result at the end of the day we like to say that
the machine is not where you make it’s not what sets a coffee apart but it’s
how you manipulate the machine that’s what sets the coffee apart the
individual coffee has all of these potentials and then you can use all of
these systems you pull those potential flavors that
you want out of the coffee so on one machine having faster air flow may cause
more citrus on another machine slowing air flow down may cause more citrus
there’s no set answer to that question I’m sorry you have to experiment with
lack of air this is true talk to me about this aroma
roast if you will you can just knock that airflow back towards the end of the
roast you could roast something super light all those pores are open towards
the end of the roast there’s a lot of smoke in the drum so if you want that
light fruity naturally processed Costa Rica to also it tastes like smoke slow
down keep the smoke in the drum and still drop it at that light drop point
you want to still get the fruit and also have a really interesting smoke no
that’s right yep and if you want a super clean coffee
you can also blast air through at the end of the roast now what some people
that I have heard admonishment too too much airflow at the end of the roast
that it could pull some of the volatile aromas off of the coffee I haven’t seen
that scientifically proven but I think that there’s a potential tip for that
but anything’s possible the world is yours I think that basically sums it up
for this week do you have any last words for us or thoughts on airflow alright
great well keep your questions coming again your questions are what kind of
drive where we go with this with the series and we need to have a lot of
leadership in in what you guys are thinking out there and what questions we
can answer and we’ll try to keep the information flowing thank you see you
next month you

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1 thought on “Roaster School Online – #16 – Revisiting the discussion on airflow”

  1. Helder Barreto says:

    Joe, I'm a simple home roaster that has bought some high quality equipment, so that I can play with these variables (airflow, check RoR, see graphics etc). I just wanted to say a big thank you for the quality of your videos and your personal capacity of being objective on the explanations. You make everything looks simple (although we know how hard it is to teach so many concepts). Thanks a lot!

  2. Brian Birdy says:

    Thank guys ! This is the gift that keeps on giving 🙏🏻❤️☕️

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