In the past 20 years, since the late l970’s, many
hundreds of people who never roasted coffee beans before, have
acquired roasting machines and/or are working for new roasting
firms, and an inordinate amount of effort, thought and discussion
has centered on how do you control the degree of roast of the
bean?
Even though Sivetz acquired his fluid bed roasting
patent in l976, and one of its major claims is the accurate thermocouple
sensing of bean temperature.
Large commercial drum roasting machines had systems
applied to measure the bean temperature, but such systems were
not available for the smaller roasting machines, and were not
furnished unless the customer requested and paid for such auxiliary
instrumentation and sampling.
Refer to the accompanying
graph that relates bean temperature
to roast weight loss, light reflectance from bean colors, and
aroma/flavor intensity.
The degree of bean roast on drum roasters has been
traditionally by sample probing and visual inspection of the bean
color, which is not an n accurate nor readily reproducible end
point. And this is why people who roast in drums have difficulties
in controlling not only the degree of roast, but to be able to
do it again and again. The dial thermometers on most drum roasters
simply indicated an environmental temperature, neither the inside
air nor the bean. At best a useless guide.
For these reasons, trying to measure accurately
bean temperatures on drum roasters was not done.
But in the Sivetz fluid bed roaster, accurately
measuring the bean temperature was an integral part of its control
system, which allowed the operator to set the degree of roast
he wanted, and also to be able to reproduce that degree at any
time.
And so today in year 2000 or 200l, the proven concept
that end bean temperature controls taste, weight loss and bean
color, has not established itself with drum roaster operators,
when in fact the large Probat and similar drum roaster fabricators
have when requested provided bean temperature measuring systems
and these are being used all over the world.
So the small drum roaster operator should avail
himself of means to accurately measure bean temperatures. One
reason such systems have come into use with the larger drum roasting
operations is that they cannot afford to make mistakes, and with
faster roasting, say 7 min or less, the controls need to be taken
out of manual hands.
The shortcomings in the use of light reflectance
meters on the ground beans is that such measurements are” after
the fact”, that is, after the roast is done, whereas, bean temperature
measurements are taken while roasting and being able to do so,
controls can be applied faster and more accurately and while in
process.
The purpose of the above explanation, on a proven
principle, is to enlighten the confused and frustrated roaster
operator to knowledge and applications well over 25 years old.
This situation is a good example of how slow enlightenment
comes to an industry.
It also illustrates the axiom; “Education is a process
of disillusionment”.
Mike Sivetz
