Baking & Snack - April 2005 - 66

PROCESSING TECHNOLOGY
ᮤ This donut fryer viewed from the exit and ready for product, clearly shows
the flipping mechanism at the halfway point of the fryer, as well as the
flighted takeoff chain conveyor.
BELSHAW BROTHERS INC.

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or electrical heating elements make cleaning very difficult. Fines that settle on the heating tubes or elements
can burn onto the units and adversely affect heat transfer.
These elements are mounted very close together, so access for cleaning is difficult.
Level control is essential for proper operation and
safety in direct-heated systems. If levels drop and the
heating elements are exposed to air, the fryer may
catch fire.
Indirect heating systems. This design uses the frying oil itself to maintain fryer temperature. The frying
oil is passed through a heat exchanger and returned
directly to the fryer. Temperature control is achieved
by inserting a thermocouple on the inlet side of the
cooker thus controlling the temperature of the fuel,
steam or thermal fluid that is used in the heat exchanger. The oil in the fryer is recirculated through
the heat exchanger approximately once each minute,
so very powerful and efficient pumps are needed in
these systems.
Indirect systems allow multizone frying systems.
With these systems, operators can process foods at
different temperatures at different points along the
fryer. Multizone cooking is only possible with external
heated systems.
Advantages include:
* Uniformity of temperature control
* Extremely high heat capacity
* No gas equipment or flames in process area

68 / BAKING & SNACK / April 2005

Generally low oil volumes
Highest thermal efficiencies
Temperature zoning possible
Clean-in-place systems usually included
Able to match oil/product velocity
Disadvantages may include:
* High initial cost
* Requires more floor space
* Pump/motor noise
Multizone fryers have multiple inlets and outlets to
control oil flow rates and the temperature differential
(∆T) in degrees F between the fryer inlet (product
infeed) and outlet or discharge end. This is of prime
importance when designing external heat exchange
systems. It also is important from a product standpoint.
For example, a 40°F ∆T is acceptable for potato chips
but would be unacceptable for donuts. ∆T is an important consideration when selecting the fryer design best
suited for a particular product.
In continuous operations, the conveyance system
through the fryer must fit the product. For products that
float, such as donuts, the product is guided by a flighted
chain. Cake donuts initially sink until the leavening acids
act, creating gas cells, prompting the donuts to float to
the surface. In this case, an initial submerged conveyor
must also be included.
Because cooking only takes place on the submerged
portion of the donut, it is necessary to flip the donuts
halfway through the fryer. Potato chips are similar. Their
buoyancy with increasing moisture loss causes them to
rise, so turning is a necessity.
There are also products that need to be fully cooked
without flipping and must, therefore, remain fully submerged in the oil. The problem is that these products may
tend to float. Because of this aspect, the products are held
under the oil as they pass through the fryer using a top
conveyor that keeps the products submerged. Fried Danish or honeybuns, are examples of products that will float
but must remain submerged for proper cooking.
Some products that sink and bob to the surface are
conveyed in a system that allows the products to rise
and then gently forces them under the surface part way
through the process.
Finally, there are products that simply sink when deposited into hot oil. A submerged conveyor catches the
unit and moves it through the system.
INNOVATIONS. The food industry, including manufacturers of fried foods, is under pressure from many sources. These pressures reflect internal mandates to operate

Baking & Snack - April 2005

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