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energy can cause dramatic shifts in chemical
composition.
Researchers identify the exact temperatures at
which these shifts occur by monitoring changes in
the specific heat of a substance as they slowly
warm it. For more on the properties of food and
cookware that affect heat transfer, see How Heat
Conducts Itself, page 277.
THE TECHNOLOGY OF
PIDding Your Gear
A PID device offers so much better control over temperature
than other devices that you may be tempted to attach one of
them to every cooker in your kitchen. Be warned: PIDding
standard kitchen gear is not for the faint of heart. PID controllers
work best on “dumb” appliances that do not have their
own microprocessor controllers, such as espresso machines
and simple ovens. PIDding a refrigerator, or any appliance
with a compressor, is a bad idea because compressors aren’t
designed to be turned on and off frequently.
In addition to the PID, you’ll need to choose a thermal
probe and a solid-state relay sized for your equipment. Attaching
the wrong relay to your appliance could have dangerous
consequences for which we cannot be held responsible.
As for the PID itself, various brands are more or less interchangeable.
Older PID controllers had to be “tuned” to each
cooker, temperature sensor, and heating element they
encountered. But fuzzy logic and other improvements have
since produced automatic “push-to-tune” devices and
instruments with continuous, adaptive tuning that demand
much less maintenance.
Temperature-logging software can display
and record data from multiple sources
simultaneously. The software is used with
an interface box that connects to as many
as twelve thermal probes. The various
probes—typically thermocouples or
thermistors, but also platinum resistance
temperature detectors on more expensive
units—can be placed in different cookers
or in different parts of a single food item.
The software can then compare temperature
differences among the probes and
track temperature changes over time.
Although not a strict necessity for cooks,
logging systems have many uses: as an aid
in developing a Hazard Analysis and
Critical Control Points plan for cooking
sous vide, for example, or as a tool for
mapping the evenness of heating in an
oven both in space and in time.
THE TECHNOLOGY OF
Controlling Temperature
Not so long ago, the mark of an expert chef lay in his ability
to control the fire and to judge how long and how close to
hold the food to it. But in this area at least, technology has
bested human expertise, and electronic instruments are
now vastly better at controlling temperature than chefs are.
A device called a proportional–integral–derivative (PID)
controller can determine not just the current temperature but
also the rate of warming or cooling of its probes and the
cumulative amount of overshoot or undershoot. It then
adjusts the rate of heat input accordingly (see Controlling the
Temperature, page 2·230). These devices combine high-end
temperature sensors with software programs and relays that
regulate a heating element. The name PID refers to the way
this software makes its calculations.
The SousVideMagic PID controller is an inexpensive device that allows an ordinary, and
inexpensive, metal rice cooker to be turned into an unstirred sous vide water bath.
The CyberQ II is a controller system for barbecues that changes the temperature of
smoke by regulating airflow to smoldering wood.
Because PID controllers prevent overshooting or undershooting the target temperature
during initial heating, they excel at reaching and holding a stable set point.
The PID controller on an Accu-Steam electric griddle replaces the simple control dial for
greater accuracy.
PIDding espresso machines was a landmark innovation that enabled baristas to deliver
coffee drinks of consistently high quality.
270 VOLUME 1 · HISTORY AND FUNDAMENTALS HEAT AND E NERGY 271