Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
Method of Manufacturing Particulate Ice Cream for Storage in Conventional
Freezers
FIELD OF THE INVENTION
[0001] The present invention relates to particulate ice cream, and more
particularly to an apparatus and method for manufacturing particulate ice
cream
having a melting point sufficient for storage within conventional dairy
freezers and
storage equipment.
BACKGROUND OF THE INVENTION
[0002] Recent developments in cryogenics have enabled the manufacture of ice
cream in particulate form using cryogenic equipment. One such method for
manufacturing ice cream is described in detail in U.S. Pat. No. 5,126,156,
which is
hereby incorporated by reference. Storing particulate ice cream made using
cryogenic techniques sometimes requires that specialized equipment must be
used.
This is because some particulate ice creams require storage temperatures which
cannot rise above -35° F. For immediate consumption, some particulate
ice creams
can be stored in freezers which do not rise above -20° F and still not
lose their free
flowing properties. However, long-term storage at this temperature is not
practicable
as the product would eventually clump together and no longer be free-flowing.
[0003] Unfortunately, conventional freezers in typical grocery dairy display
freezers range in temperature between -10° F and +0° F, and also
have an
additional albeit temporary rise of 10° F during a one-hour defrost
cycle (exact times
and temperatures can vary). Thus, conventional grocery dairy freezers can be
at
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+10° F for as long as one hour. Even worse, some grocery dairy freezers
do not
always operate at optimum conditions, are leaking or are in need of repair in
some
way, so that they may reach temperatures as high as +15° F for short
periods.
Home freezers are more stable and usually range between 0° F and
+5° F. They
have a defrost cycle but it usually does not affect the interior temperature.
In either
case, particulate ice cream made using traditional methods cannot withstand
such
temperatures without clumping or outright melting. Consequently, a method of
manufacturing particulate ice cream which can be stored in typical retail
dairy case
environments is desired.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Fig. 1 is a cross-sectional elevational view of the present invention;
[0005] Fig. 2A shows a sucrose molecule;
[0006] Fig. 2B shows a sucralose molecule;
[0007] Fig. 3 shows a erythritol molecule; and
[0008] Fig. 4 shows a xylitol molecule.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0009] Before explaining the disclosed embodiment of the present invention in
detail it is to be understood that the invention is not limited in its
application to the
details of the particular arrangement shown, since the invention is capable of
other
embodiments. Also, the terminology used herein is for the purpose of
description
and not of limitation.
[00010] Fig. 1 shows a cryogenic processor constructed in accordance with the
preferred embodiment of the present invention to produce free-flowing beads
56. A
cryogenic processor 10 includes a freezing chamber 12 that is most preferably
in the
form of a conical tank that holds a liquid refrigerant therein. A freezing
chamber 12
incorporates an inner shell 14 and an outer shell 16. Insulation 18 is
disposed
between the inner shell 14 and outer shell 16 in order to increase the thermal
efficiency of the chamber 12. Vents 20 are also provided to ventilate the
insulated
area formed between the shells 14 and 16. The freezing chamber 12, as shown in
Fig. 1, is a free-standing unit supported by legs 22.
[00011] Refrigerant 24, preferably liquid nitrogen, enters the freezing
chamber 12
by means of refrigerant inlet 26. The refrigerant 24 is introduced into a
chamber 12
through inlet 26 in order to maintain a predetermined level of liquid
refrigerant in the
freezing chamber because some refrigerant 24 can be lost by evaporation or by
other means incidental to production. Gaseous refrigerant that has evaporated
from
the surface of the liquid refrigerant 24 in freezing chamber 12 primarily
vents to the
atmosphere through exit port 29 which cooperates with the vacuum assembly 30,
which can be in the form of a venturi nozzle. Extraction of the frozen beads
56
occurs through product outlet 32 adapted at the base of the freezing chamber
12.
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[00012] An ambient air inlet port 28 with adjustment doors 38 and exit port 29
with
adjustment doors 39 are provided to adjust the level of gaseous refrigerant
which
evaporates from the surface of the liquid refrigerant 24 so that excessive
pressure is
not built up within the processor 10 and freezing of the liquid composition in
the feed
assembly 40 does not occur.
[00013] A feed tray 48 receives liquid composition from a delivery source 50.
Typically, a pump (not shown) drives the liquid composition through a delivery
tube
52 into the feed tray 48. A premixing device 54 allows several compositions,
not all
of which must be liquid, such as powdered flavorings or other additives of a
size
small enough not to cause clogging in the feed assembly 40, to be mixed in
predetermined concentrations for delivery to the feed tray 48.
[00014] In order to create uniformly sized beads 56 of frozen product,
uniformly
sized droplets 58 of liquid composition are required to be fed through gas
diffusion
chamber 46 to freezing chamber 12. The feed tray 48 is designed with feed
assembly 40 that forms droplets 58 of the desired character. The frozen
product
takes the form of beads that are formed when the droplets 58 of liquid
composition
contact the refrigerant vapor in the gas diffusion chamber 46, and
subsequently the
liquid refrigerant 24 in the freezing chamber 12. After the beads 56 are
formed, they
fall to the bottom of chamber 12. A transport system connects to the bottom of
chamber 12 at outlet 32 to auger or carry the beads 56 to a packaging and
distribution network for later delivery and consumption. After having reached
the
outlet 32, the beads 56 are entirely free-flowing and do not stick together.
[00015] The vacuum assembly 30 cooperates with air inlet 28 and adjustment
doors 38 so that ambient air flows through the inlet and around feed assembly
40 to
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ensure that no liquid composition freezes therein. This is accomplished by
mounting
the vacuum assembly 30 and air inlet 28 on opposing sides of the gas diffusion
chamber 46 such that the incoming ambient air drawn by the vacuum assembly 30
is
aligned with the feed assembly. In this configuration, ambient air flows
around the
feed assembly warming it to a sufficient temperature to inhibit the formation
of frozen
liquid composition in the feed assembly flow channels. An air source 60,
typically in
the form of an air compressor, is attached to vacuum assembly 30 to provide
appropriate suction to create the ambient air flow required.
[00016] As stated, it is a goal of the present invention to increase the
freezing point
of the beads 56 of the present invention. This is because it is a commercial
advantage of the present invention that the beads 56 can be stored either in a
home
freezer or in a conventional grocery dairy freezer, which as stated ranges in
temperature between -10° F and +0° F with an occasional rise to
+10° F. One way
to accomplish this is to reduce the freeze point depression of the liquid
composition
that forms the beads 56, although the present invention should not be
considered as
limited thereto.
[00017] Most ice creams are composed of a mixture of air, water, milkfat,
nonfat
milk solids (NMS), sweeteners, stabilizers, emulsifiers, and flavors. As
stipulated by
the United States Department of Agriculture (USDA), ice cream is produced by
freezing, while stirring, a pasteurized ice cream mix containing at least 10%
milkfat
and 20% total milk solids (TMS). The finished ice cream product must weight at
least 4.5 Ib/gal and must contain at least 1.6 Ib of food solids or total
solids (TS) per
gallon, while a minimum total food solids must be 35.6%. It is impermissible
to fall
below these limits, or if one does then the finished product cannot be labeled
ice
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cream.
[00018] The freezing point of the ice cream mix of the present invention which
forms the beads 56 can be increased by making adjustments to one or more of
the
above components, and some adjustments work better in combination with each
other. The first component is non-milk solids (NMS) content, the second is the
stabilizers, the third is the emulsifiers, the fourth is the total solid (TS)
content, and
the fifth and perhaps most complex is the sweetener content.
Non Milk Solids (NMS)
[00019] NMS or serum solids enhance the texture of ice cream, aid in giving
body
and chew resistance, and may be less expensive than milkfat. However, milkfat
may
be substituted for NMS, but under USA federal government requirements only up
to
14%. Whey solids, including modified whey products, may also be substituted
for
NMS but under USA federal government requirements not for more than 25% of the
total NMS in the entire mix.
[00020] Egg yolk solids can also be used as NMS within the present invention.
Egg yolk solids impart a delicate flavor, and also improve the body and
texture of the
resulting ice cream. Egg yolk solids also improve fat structure formation,
presumably
due to lecithin existing in a lecithin-protein complex, which can act
similarly to an
emulsifier. Egg yolk solids have almost no effect on freeze point depression,
are
high in food value, but unfortunately can increase the cost of the mix.
[00021] Dry whey solids can also be used as NMS within the ice cream mix of
the
present invention, because they are relatively inexpensive. Whey is the watery
part
of milk and contains most of the milk sugar in milk. As stated, federal
standards in
the USA permit substitution of whey solids for up to 25% of the NMS. However,
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unprocessed whey can cause a lower freezing point and potential for a sandy,
grainy
feel to the finished ice cream product. To address this, an increasing number
of
whey products are available that are processed to have high protein, reduced
lactose contents, and a higher molecular weight. This higher molecular weight
in
turn means these processed whey products reduce the freeze point depression of
the overall mix.
[00022] One means to process whey to have more desired characteristics is
through a process known as ultrafiltration, in which a whey solution is
repeatedly
passed through a membrane that filters out components with a high molecular
weight, such as high-protein whey, while passing components with a low
molecular
weight, such as water, salts, and lactose. This process results in a products
known
as whey protein concentrates (WPCs).
Stabi liters
[00023] The primary purposes for using stabilizers in the ice cream of the
present
invention are to increase mix viscosity, to stabilize the mix to prevent
wheying off or
separating, to retard or reduce ice and lactose crystal growth during storage
especially during periods of temperature fluctuation also known as heat shock,
to
slow down moisture migration from the product to the package or the air, to
provide
uniformity to the product and resist melting, and to provide smoothness in
texture
during consumption. Retarding ice crystal growth is especially valuable
because
smaller ice crystals within the beads 56 result in a better taste and
mouthfeel of the
resulting ice cream product.
[00024] The stabilizers of the present invention must also have a clean,
neutral
flavor, and not bind to the intended ice cream flavors. Although stabilizers
have little
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or no impact on the size of ice crystals at time of initial freezing, they do
limit the rate
of growth of ice crystals during recrystallization (where thawing and then re-
freezing
occurs). This could be due to a range of factors, including surface adsorption
to the
ice crystal itself, modifying the rate at which water can diffuse to the
surface of a
growing ice crystal during temperature fluctuations, and modifying the rate at
which
solutes and macromolecules can diffuse away from the surface of a growing ice
crystal.
(00025] Additionally, many fish, insects, bacteria, and plants have the
ability to
tolerate or avoid freezing in their natural environments by secreting groups
of
proteins that have the ability to depress their freezing point (anti-freeze
proteins),
and/or resist the rate of ice recrystallization (ice structuring proteins or
ISPs). When
an ISP is introduced into an ice cream mix as a stabilizer or to act in
support of a
stabilizer, the ISP adsorbs to the surface of an ice crystal, thus blocking
further
growth of ice at that crystal surface. ISPs are desired where a stabilizer is
not
sufficiently effective or is undesirable in formulation.
[00026] In the ice cream mixes of the present invention, another type of
stabilizer
used is carrageenans, which act as a secondary hydrocolloid to prevent wheying
off
or separating of the ice cream mix, an undesired condition caused by the
incompatibility of other stabilizers. At typical use levels, carrageenan
contributes
very little to viscosity in hot ice cream mixes which are heated as part of
the
pasteurization process referred to earlier. However, as the ice cream mixes
cool, the
stabilizer carrageenan undergoes a conformational change from a coil to a
helix, at
around 40° C. The helical forms produce structures that increase
viscosity and
create a weak gel that is easily broken by shear forces. This gel is capable
of
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holding dispersed particles in suspension, and as it cools can help stabilize
casein
micelles to prevent further phase separation. This improves resistance to
separation
of protein and polysacchararide rich phases in ice cream mixes, thereby
improving
resistance to melting of the resulting ice cream.
[00027] Stabilizers, among other functions, are also responsible for absorbing
free
water sometimes present within the ice cream mix. Stabilizing agents are also
used
to give texture, body, stiffness and alter the melting properties of ice
cream. These
are especially important in particulate ice cream such as that of the present
invention, because forming-the beads 56 in a spherical shape and the resulting
free-
flowing properties generated therefrom is critical to commercial success. The
stabilizers accomplish this by binding up any free water that has not already
frozen,
and preventing that free water from freezing into large undesirable crystal
sizes more
often found in conventional ice cream, or in ice cream that has been in the
freezer
too long.
Emulsifiers
[00028] Emulsifiers are usually integrated with stabilizers within the ice
cream mix
of the present invention, although they perform a very different function from
stabilizers. Emulsifiers are used to produce a stable suspension of two
liquids that
do not mix naturally. In ice cream, the two liquids would be a fatty solution
and
water. The colloidal structure of ice cream begins with the mix as a simple
emulsion,
with a discrete phase of partially crystalline fat globules surrounded by an
interfacial
layer comprised of proteins and surfactants, and also water. To keep these
ingredients stably suspended, an emulsifier is used. The emulsifiers lower the
fat/water interfacial tension in the ice cream mix, resulting in protein
displacement
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from the fat globule surface, which in turn reduces the stability of the fat
globule
thereby allowing partial coalescence of that fat globule during the freezing
process of
the bead 56. This partial coalescence leads to the formation of a structure of
the fat
that beneficially contributes to texture and melting properties within the
finished ice
cream product. The texture of ice cream is an important quality attribute,
because
texture is the sensory manifestation of structure.
[00029] During the freezing stage, another dispersed phase of ice crystals are
formed within the emulsion of ice cream mix. Air bubbles and ice crystals
usually
range in size from 20 pM to 50 pM and are surrounded by a temperature-
dependent
unfrozen phase. In addition, as stated the partially crystalline fat phase
undergoes
partial coalescence during the freezing process, resulting in a network of
agglomerated fat bodies which partially surround the air bubbles, thus giving
rise to a
somewhat solid-like structure. Emulsifiers can include both mono- and di-
glycerides,
although within the present invention diglycerides are preferred because of
their
higher atomic weight. The concept of glycerides will be discussed in more
detail
infra, but suffice for now to say that glycerides are often associated with
sweeteners.
Thus, depending on the type of sweetener used, a sweetener can also act as an
emulsifier.
Freezing Point in general
[00030] To understand the next parameter, total solids (TS), it is necessary
to
specifically describe the freezing process. The freezing point of ice cream is
dependent on the concentration of the soluble constituents therein. The
amounts of
sweetener solids and lactose concentration can affect the freezing point of
any ice
cream mix. However, when latent heat is removed from water and ice crystals
are
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formed, a new freezing point is established for the remaining solution, since
it has
become more concentrated in respect to the soluble constituents. As more and
more water is turned into ice, the remaining fluid phase becomes increasingly
viscous, because ice is essentially pure water that other molecules get
excluded
from during formation of ice crystals. Consequently, the freezing point of the
unfrozen phase of the ice cream mix is lowered.
[00031 ] In freezing ice cream, the freezing point is being continuously
lowered by
crystallization of water and concentration of solutes (called freeze
concentration), so
that the temperature of the mix continues to drop, but drops at a slower rate.
Thus,
the refrigerant 24 referred to above (Fig. 1 ) must remove both latent heat of
fusion
due to crystallization, but also the sensible heat necessary to lower the
temperature
of the ice crystal slurry.
[00032] When the concentration of dissolved substances increases to a point
where only about 18-20% of the original water remains unfrozen, the freezing
point
of the mix reaches a temperature at which no more ice can be formed. This
point is
often called the glass transition temperature. Within this state, the water in
the ice
cream can never be completely frozen, even at very low temperatures. At normal
manufacturing and storage temperatures, a significant portion of the water
remains
in the liquid state, a factor that favorably influences the stability of ice
cream.
Introduction of ISPs can help dictate when an ice cream mix reaches the glass
state.
[00033] Nonetheless, formation of the correct amount of ice during freezing is
not
sufficient to guarantee a high quality ice cream. The average size and
distribution of
sizes of ice crystals has a significant impact on smoothness and eating
quality of ice
cream. The freezing operation of the present invention intentionally produces
mostly
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small crystals to yield an ice cream with a smooth mouthfeel. This is partly
due to
the rapidity at which the ice cream droplets 58 are frozen into beads 56.
Because
the freezing process is very rapid, taking perhaps two minutes at most, the
ice
crystals form much more quickly and are much smaller. Many other factors
mentioned herein also lead to formation of smaller ice crystals within the
beads 56,
[00034] Although many factors influence the mouthfeel of ice cream, it is
generally
understood that the majority of ice crystals should be smaller than 50 uM in
size, and
hopefully around 20 uM. If many crystals are larger than this, the ice cream
will be
perceived as coarse or icy.
Total Solids (TS)
[00035] Total solids (TS) replace water in the ice cream mix, thereby
increasing
the nutrititive value and mix viscosity and improving the body and texture.
Egg yolk
solids, for example, can reduce the freezing time of the resulting ice cream.
Increasing the percentage of total solids decreases the percentage of frozen
water in
the resulting ice cream, which improves taste and texture. In frozen ice
cream, water
is present both as a liquid and as a solid, as not all water freezes due to
the effect of
the added solutes on the freezing point depression. The solid/liquid ratio
affects the
firmness of the ice cream.
Sweeteners
[00036] It is known that sugars do not dissociate in solution, so that the
freezing
point of solutions contain various sugars can be accurately computed from
their
concentration and molecular weight. Many ice cream mixes use sucrose as a
sweetener, which has a freeze point depression of 2.5° F. This freeze
point
depression can be decreased by substituting sucralose for sucrose, potentially
in
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combination with other sugars or sweeteners. Such a substitution can increase
the
freezing point (decrease the freeze point depression).
[00037] Sucralose is made by converting sugar to a no calorie, non-
carbohydrate
sweetener. As shown in Figs. 2A and 2B, this conversion process selectively
replaces three hydrogen-oxygen (hydrox) groups on the sucrose molecule with
three
chlorine atoms. This converts the sucrose (Fig. 2A) within sugar to sucralose
(Fig.
2B), which is essentially inert and has a higher molecular weight than
sucrose. This
is because the atomic weight of a hydrox group is approximately 17, while the
atomic
weight of chlorine is approximately 35.3, thereby making a difference of
approximately 18.3 atomic units. Multiplying this difference times three means
there
exists a significant difference in the molecular weight of sucralose and
sucrose. The
result is a stable sweetener that tastes like sugar, but because of its higher
molecular weight has a lower freeze point depression than sucrose.
[00038] After consumption, sucralose passes through the body without being
broken down for energy so it has no calories. Sucralose is consider 600 times
sweeter than sugar, and remains stable during pasteurization treatment, which
can
raise the temperature of the ice cream mix to 40° C. However, because
sucralose is
so much sweeter than sucrose, unlike sucrose it is difficult to also use
sucralose as a
NFS or TS. This is because the volume of sucralose needed to achieve a
specific
sweetness is several magnitudes less than the sucrose. Thus, any attempt to
use
sucralose in bulk volumes would make the resulting ice cream mix excessively
sweet.
[00039] Although sucralose is made from sugar, the body does not recognize it
as
sugar or a carbohydrate. Also, sucralose is not metabolized by the body, so it
is
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calorie-free, and does not affect blood glucose levels. Sucralose also has no
effect
on carbohydrate metabolism or insulin secretion.
[00040] There exists a group of sugar alcohols, known as polyols. These
polyols
are somewhat of a hyrbrid between sugar and alcohol. Polyols include among
others erythritol, xylitol, and maltitol. Inclusion of these specific sugar
alcohols in an
ice cream mix results in a much lower glycemic index, which is suitable for
diabetics.
However, besides being appropriate as sweeteners, these sugar alcohols can
also
function as bodyinglbulking agents or NMS, and can also act as ice
crystallization
inhibitors. Also, polyols do not contribute to tooth decay. This is because
polyols
are resistant to metabolism by oral bacteria which break down sugars and
starches
to produce the specific acids which can lead to tooth enamel loss and cavity
formation. Polyols are, therefore, non-cariogenic.
[00041 ] One polyol that is useful within the present invention as a sweetener
is
erythritol, which has excellent heat stability. Erythritol does not decompose
even at
temperatures as high at 160 °C. This is an advantage during the
pasteurization
process which is a necessary step in preparation of the ice cream mix.
However,
being a monosaccharide, as shown in Fig. 3, erythritol has a lower molecular
weight
than sucrose, and has only four carbon atoms.
[00042] Erythritol is also safe for people with diabetes. Single dose and 14-
day
clinical studies demonstrate erythritol does not affect blood serum glucose or
insulin
levels. Clinical studies conducted in people with diabetes conclude that
erythritol
may be safely used to replace sucrose in foods formulated specifically for
people
with diabetes.
[00043] Another polyol used as a sweetener within the present invention is
xylitol,
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which as shown in Fig. 4 has five carbon atoms rather than six. Xylitol's five-
carbon
molecule has strong chemical bonds that are very difficult for oral bacteria
to digest.
Thus, when foods containing xylitol are consumed, these oral bacteria
populations
starve out and decline. Accordingly, foods containing xylitol cause less tooth
decay.
[00044] Another polyol used in the present invention is maltitol. Maltitol is
also
known as hydrogenated maltose, a disaccharide with a molecular weight
comparable
to sucrose.
[00045] Polydextrose is a low-calorie bulking agent that can be used at
significant
concentration without affecting viscosity, yet because of its high molecular
weight
has a freezing point depression significantly smaller than sucrose.
[00046] Dextrose, being a monosaccharide, causes greater freezing point
depression than sucrose, maltose, or lactose, which are disaccharides.
However, in
small proportions, dextrose can also be used as an ingredient within the ice
cream
mix of the present invention without noticeably affecting the freezing point.
Finally,
aspartame, acesulfame K, neotame, and saccharin can also be used as sweeteners
within the present invention. Neotame is particularly advantageous because it
has a
much higher molecular weight (C20 H30 N2 05) than sucrose.
[00047] The various aspects of the present invention has been described in
detail
with particular reference to preferred embodiments thereof, but it will be
understood
that variations and modifications can be effected within the spirit and scope
of the
invention as described herein. It is anticipated that various changes may be
made in
the arrangement and operation of the system of the present invention without
departing from the spirit and scope of the invention, as depicted in the
following
claims.
