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Topic: First FR+/ dual variac roast (7 msgs / 135 lines)
1) From: Jim Schulman
Got my tiny (only 4 lbs) 3 amp variac, and just 
did my first roasts with separate fan and heat 
control. The plan was to compare full and varied 
fan roasts with the same temperature profile; but 
that'll have to wait until I get more skilled at 
this.
Some notes: 
1. I upped my dose from 80 to 96 grams, used the 
added airflow from the variac, and got a nice even 
color going into the first crack; so I thought I 
was set. Then my first surprise; the roasts turned 
uneven close to the finish. Since the beans are in 
a vertical column in the FR, maybe there's a 
height limit late in the roast when the beans have 
expanded; or maybe I need to add an inch to my 
roast chamber extensions.
2. Changing the airflow alters the thermal 
dynamics in the FR fairly drastically. At full 
flow roasts, I basically keep nudging the heat up. 
On the minimum flow roasts (reducing fan speed to 
just keep the beans circulating), I also reduced 
the heat to keep the airtemperature inflow air 
temp fairly constant. Nevertheless, the bean temps 
(measured at the outflow) tended to "run away" at 
several points in the roast, and I had to 
dramatically reduce heat to get the temperature 
rise rate back to profile. Maybe roasting is 
nuclear science after all, and "exothermy" 
requires some sort of critical mass.
In any case, it'll take some time until I sort all 
this out. Won't be able to say how varied flow 
versus full flow tastes till then.
Jim
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2) From: Ken Mary
<Snip>
My preference for faster roasts has led me to forget about reducing the
heat, I just vary the airflow to create my desired profile.
You may find it easier to use only one or a few defined heat settings and
vary the airflow. My problem with runaways only occurred with underpowered
roasters approaching second crack. I believe that if the airflow falls below
that needed for efficient mixing (and heat transfer) the temperature will
vary unpredictably. You need enough heat input so that the airflow will be
high enough at all times to enable manual flow adjustment without "going too
far".
--
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3) From: Ben Treichel
 From an earlier post, here is what I do with my dv FR+.
Here's a profile to try.  4 minutes to 375, 4 minutes to 400, and 4 
minutes to 425, and then whatever else time needed to get where you 
want. If I set the voltage to 102.5 and hold it to 375, and then step 
down to 95, its close to the 4/4/4 profile. I came up with this profile 
thinking that since most of the interesting stuff happens between 375 & 
425 (and beyond) that that was where I wanted to spend most of my time.
Ken Mary wrote:
<Snip>

4) From: Jim Schulman
On 16 Feb 2003 at 10:01, Ben Treichel wrote:
<Snip>
I guess I'm a "medium," roast time: 4 - 5 minutes 
to 350F, another 5 to 440/450F. 
Ken, I think you're probably right about keeping 
the flow higher than bare minimum; at least at the 
heat settings between 107 and 110 I was using. 
Ben, it sounds like you're using both lower heat 
and airflows towards the end of the roast than I 
did.
Thanks for the tips. It's really cool how 
differently the same machine can be made to do 
tasty roasts with a few minor mods. Guess I'll 
just have to put in 20 odd roasts before I find 
out what works for me.
Jim
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5) From: Ben Treichel
Jim Schulman wrote:
<Snip>
I'll run about 17.5 volts on the variac to lift the 4 oz green, and 
eventually drop the voltage to around 15. I look for a nice fountain 
action, not with the beans still in contact. If it starts to raise them 
in layers, or really blow them around I lower the fan voltage. FYI, I 
have about 1" of soup can on top of my chamber, before the chaff 
collector, to get enough space for the beans.
<Snip>
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6) From: Jim Schulman
On 16 Feb 2003 at 14:12, Ben Treichel wrote:
<Snip>
Ah, you bypassed the drop down resistor on the 
motor, and are using the variac set really low. 
Maybe I'll do that to pick up more fan power.
I already have about an inch extender on my 
chamber, so no need to change anything there.
Jim
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7) From: Ben Treichel
<Snip>
I wired directly to the bridge. This also lets you cut out the secondary 
heater which functions as the drop down resistor. By doing this you can 
get 2:00, or even sub 2:00 cool down times to 200F.
Just be careful, I know you can let the magic smoke out of the motor 
around 25 volts ac (maybe lower).
Also, you might want to cut off the thermal limit switch (reed type 
switch), if you haven't. It can open up and mess up your temperature ramp.
<Snip>


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