Texas Bakery Automates Minor Ingredient Addition
Bread baking techniques
have changed greatly since Stone Age man crushed wheat into flour, then baked
his loaves on hot stones. Today's bakery is highly automated and one good
example of this is the Mrs Baird's Bread plant in Fort Worth, Texas. The Fort
Worth plant has been in full production since June 1992.
In business since 1908,
Mrs Baird's Bakeries,
Inc. is the largest
family-owned bakery in the United States. In eleven bakeries throughout the
state of Texas, the company produces over 150 different bread and cake products.
Throughout the entire product line, two characteristics are paramount-quality
The new plant, adjacent to
Fort Worth's south freeway cake plant, replaced a 75-year-old plant downtown.
"From the start, our design of the plant was product driven rather than
technology driven," explained Mrs Baird's Project Engineer David Pait.
"Automation was important because it could provide the consistency we wanted.
Consequently we were able to put more science into the art of baking."
One area where product
quality took precedence over technology was in the addition of yeast. Yeast
needs to be added to the sponge mixer at exactly the right time in the mix
cycle. Various methods of doing this were evaluated, but Mrs Baird's decided
they obtained the best results by keeping this a manual operation. 50-pound
blocks of yeast are kept in cold
Nine loss-of weight feeders, all with extended helixes,
deliver materials simultaneously to a central hopper where they are immediately
transferred to one of the six mixers. A second circle of eight feeders completes
the minor ingredient feeding system.
storage near the mixers.
The computer signals the operator at the proper time and he adds the yeast by
Dry vs. Liquid Systems
One of the key decisions
made early on was to go with a dry system for the handling of minor ingredients.
Other Mrs Baird's Bakeries used liquid systems where the minors were delivered
to the mixers in a slurry state. However, they felt a dry system with individual
weigh-up containers could lead to a more flexible system and a cleaner
After evaluating three dry
systems, one supplied by Frank Haile & Associates was chosen. Haile provided the
design engineering and installation of the dry system which included silos,
butterfly valves, feeders/ hoppers, receivers and check scales at the mixers.
"Accuracy was critical to our equipment selection," Mr. Pait stated. "Delivery
and price entered into it, but...
The two-story structure includes bag dump and receiving
hoppers on the second level supplying material to the loss-of weight feeding
we had to have the
accuracy to achieve our consistency goal.” There are up to 17 minor ingredients
currently added to the various recipes. Because of this wide variety, material
handling expertise also became an important factor in vendor selection. Bulk
densities varied from very light-almost fluffy-materials such as bran to fairly
heavy materials like salt. Challenging materials to feed included one that was
hygroscopic and one that caked easily.
The 17 minors in total
comprise only about 10% of the 1600-pound batches. Each of the 17 ingredients
had to be delivered within 1/10 pound of the desired weight. AccuRate, Inc. of
Whitewater, Wisconsin was able to feed all the materials, meeting the required
accuracies, and was selected to provide the system's loss-of-weight feeders.
Flexible Hopper Feeders
The stainless steel
feeders contain a Tuf-Flex vinyl feed hopper. Two alternating paddles press
against the outside of this flexible hopper. This conditions the material inside
to a uniform bulk density. Each flight of the extended feed screw is completely
filled with material, resulting in precise delivery of material into the central
Each feeder sets atop a
scale that counterbalances out the dead weight of the feeder and hopper,
weighing only the material inside. "We have level controls on the storage
hoppers and keep the scale size as low as practically possible," Pait explained.
"This way we maximize the resolution of the load cell and get the best
The feeders are set up in
two circles, with nine feeders in one and eight feeders in the other. Each
feeder has an extended helix, varying in length from 3' to 5', to transport the
respective ingredients into a central receiving hopper.
Eleven of the feeders are
supplied from bag dump stations on the second floor of the dry system. The mixer
operator loads 40-50 pound bags into these bag dump hoppers. The powders drop
from the bag dump hoppers into extension hoppers atop the feeders. The other six
ingredients are purchased in larger bags or super sacks. These bags are unloaded
on the ground floor and piped up to the mezzanine into receivers and 50 cubic
foot storage hoppers above the feeders.
All the minor ingredients
must be fed and transferred to the mixer within 2 minutes. The AccuRate
loss-of-weight system, with each feeder atop its own scale, allows the
transferring to begin as soon as the weighed feeding begins, as opposed to a
gain-in-weight system where the ingredients discharge into a central scale and
the entire batch is transported to the mixer after being weighed. The
loss-of-weight system allows a longer actual batch time for the feeders, which
contributes to their precision.
"The feeders are so
consistent we haven't had to use their DRIBBLE speed. We deliver the entire
batch in the FAST speed," Pait said. "We use the PREACT setting to zero in on
the exact amount we need. Once we learned the proper PREACT for each ingredient,
we were always within our 1/10-pound tolerance. We’ve even sped up our feed
rates three times with no problem.”
Sponge and Trough Process
There are six mixers in
the plant-two sponge mixers and four dough mixers. The two-stage mixing process
begins with the addition of flour, water, yeast, and yeast food into a sponge
mixer. After about 12 minutes, the sponge is discharged into a 1600-pound
sanitary steel trough (pronounced troe) and automatically taken to the
fermentation area. Here it rises naturally under controlled temperature
conditions for about 3½ -4 hours.
The expanded sponge then
goes to one of the two final mixers. More flour and other ingredients are added
and mixed for about 12 minutes. The dough discharges into a trough and is moved
to the divider where it is cut into pieces.
After being rounded, the
loaves go into the intermediate proofer where they "rest" for 4 minutes while
being conveyed to the moulder.
Expert Control System
After a mixer discharges
its sponge or dough, it automatically calls for a new batch. A working table
inside the computer picks the proper recipe for the requesting mixer, and the
bulk, liquid and minor systems begin operating.
An Allen Bradley PLC
system with a UNIX platform host computer controls all plant operations. Next to
each mixer is a panel view screen which gives the operator an up-to-the-minute
report on variables such as desired/actual amount of each ingredient; number of
batches completed; and mixer parameters such as motor RPM, temperature and mix
"Basically, we have an
expert system that's been taught how to bake a loaf of bread," explained Mrs
Baird's Ron Huffman. Huffman was instrumental in developing the host computer
software for the bakery. The host computer has access to everything on the PLC
level. It can function as an operator, making decisions based on available
information, or it can be interactive.
Just-Baked Freshness Still Possible
Time is critical
throughout every stage of the Mrs Baird's process. "It takes six hours from raw
ingredient to wrapper. Then we have to get it to the shelf," Pait stated. "This
is another area where we can excel. With eleven bakeries, plus a large truck
fleet, we know we're delivering the freshest product possible"
Each driver has a
hand-held computer to record data at each route stop. At the end of the day,
each unit is plugged into the main computer at the plant and the next day's
production schedule is generated.
Even with automation
leading to a production rate of 100 loaves per line per minute, Mrs Baird's
still promises each customer a product "Baked With Family Pride."