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5000 Series Manual Page 7
Carburetor Assembly
Your new freezer uses a metering device, known as a carburetor, to feed the proper ratio of mix and air into the
freezing cylinder. For products such as dairy based shake mixes, the proper mix to air ratio is generally accepted to
be two parts mix to one part air. This proportion yields a finished product that is both tasty and profitable. At this
ratio, one gallon of liquid mix will yield a volume of one and one-half gallons of frozen product.
The carburetor is a tube with a hole, or series of holes, bored through the side. It is located in the hopper and fits in
a hole that leads to the freezing cylinder. Air flows into the freezing cylinder through the top of the tube and mix
flows in through a smaller hole in the side of carburetor tube. The size of the mix inlet is balanced with the viscosity
(thickness) of the liquid mix and product draw rate, in such a way that the proper amount of mix is fed into the freez-
er cylinder to blend with air at just the right ratio. Mix viscosity varies by mix type, mix temperature, and mix age.
Different serving rates also demand different feed rates. The Crathco carburetor has an outer sleeve that can be
rotated to line up with different hole sizes to provide ideal overrun under all operating conditions.
You will need to experiment to determine how much mix to add to the freezing cylinder at start-up. This can be done
by watching the level of mix through the clear plastic dispensing valve when filling the hopper. When the correct
amount of mix feeds into the freezing cylinder install the carburetor tube in the "Off" position (outer sleeve set
between any two holes) and turn the freezer "ON" to freeze down to proper consistency.
Overrun
Overrun is the increase in product volume, expressed as a percentage, resulting from the entrapment of air in liquid
mix as it is frozen.
The rotating dasher blends air into the mix as it is frozen, resulting in increased product volume. For example, if one
gallon (4.4 liters) of liquid mix is poured into a freezer and one and a half gallons (6.6 liters) of frozen product is
drawn out, the result is a fifty percent volumetric increase, or a fifty (50%) percent “overrun”.
Why is overrun important? The introduction of air into the finished frozen product is essential from two
standpoints...taste and profitability. Frozen product with a low percentage of overrun costs more to serve, appears
wet, and is heavy. The introduction of air makes the finished frozen product taste richer. Too much air causes the
finished product to be too light and fluffy, making it less satisfying and adversely affecting sales. The optimum
percentage of overrun varies from one type of mix to another, but 50% overrun is a good average. The ingredients
in some mixes take on and hold air easier than others. Overrun also affects profitability. For example, an increase
from 25% to 50% overrun represents a mix savings of 17%.
Uniform overruns ensures consistent portion costs. If overrun is allowed to drop, it will cost more to serve a portion
of finished product.
Computing Overrun
1) Weigh an empty cup.
2) Weigh this cup filled to the top with liquid mix, and subtract the weight of the cup.
Note: Repeat this step only when changing mix sources, as mix weight will vary slightly from one supplier
to another.