What is overrun?
Overrun is the term
for the percent of expansion of ice cream achieved from the amount of
air incorporated into the product during the freezing process. An
overrun of 50% means that it has expanded 50% (for example: one gallon
of mix will make one and a half gallons of finished product).
"Gravity" fed units typically yield on average about 35% overrun.
"Pressurized" units can yield 65% overrun or greater. For best quality
and appearance of soft serve a 50-60% overrun is the most desirable.
How well the machine is operating as well as if it is "gravity" or
"pressurized" affects the overrun that is ultimately attainable.
Why It matters
Overrun shows in both
the appearance and taste of the ice cream and your profitability. Soft
serve with the optimal overrun is dry in appearance and stands up well
without drooping. Many people may say that a product is "too warm"
when in fact it is cold enough but lacks the proper amount of air
which gives it structure and body. Think of the example of whipping
cream. Without air it looks like milk. After air or "overrun’ is
whipped in it gains body and can be turned upside-down. Product that
is over beaten loses the ability to hold air. Some machines try to
compensate for the lack of overrun by driving down the temperature of
the product Although it helps to "stiffen it up" the product becomes
icy and loses its creaminess and taste. Overrun also affects profits
by the perceived amount of product that is being served. Without
enough overrun you’re forced to make a choice. To maintain your
product costs you either serve a "small" cone and make a disgruntled
customer or give away more product. Higher overrun makes creamy ice
cream and a "big" cone.
65% vs. 35% overrun (both at
use pumps to transfer the mix to the freezing cylinder and pressurize
it. Some machines use piston pumps with "O" rings and check
mechanisms. Some use peristaltic tubes that require no lubrication and
have many fewer parts. This makes for easier cleaning. The amount of
pressurization ranges from 18# to 30# depending on the brand of
machine and design of the pump. The higher the pressure the better the
air incorporation. (Hint: Electro Freeze pressurized machines use 30#
How the pumps are controlled (turned on and off) is very important.
The best systems use pressure switches that maintain the correct
pressure, air and mix. Some machines use less desirable "timed pumps"
that turn on during product draw and remain on for a "timed" amount
after the end of the draw. They can not compensate for varying draw
speeds or volumes so careful timing of the draw rate is required. To
assure the barrel is pressurized enough the pump is timed so that it
pumps more than enough and then "blows off" excess pressure back into
the mix reservoir after every draw. This shows as bubbles in the
hopper and low/inconsistent overrun. Electro Freeze machines do not
use "timed pumps".
Overrun can be
calculated by weighing a container (pints are most often used) and
making a note of it so it can be subtracted later. Note how much the
container weighs filled with your liquid mix and subtract the
container weight. Once noted both numbers can be used again whenever
you want to check your overrun. Fill the same container level with
frozen product and note its weight. Now just plug it in to the
(Wt. of mix - Wt.
of same vol. of ice cream)/Wt. of same vol. of ice cream x 100% =
Example: Container =
1 oz., container with mix = 19 oz. Subtract the container weight for a
mix Wt of 18 oz. Container with leveled-off ice cream 13 oz (-1 oz of
container wt )= 12 oz. ice cream. (18-12)/12 x 100%. = 50% overrun.
...or buy an overrun scale! J
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