Ice cream

Ice cream and related products

It’s a smooth, sweet, cold food prepared from a frozen mixture of milk products
and flavorings, containing a minimum of 10 percent milk fat and eaten as a snack
or dessert.
Typical composition of ice cream contains:

10 % Fat, 11% Milk solids-non- fat
14% Sugar, 0.5 % Emulsifier & Stabilizer

64.5% Water
(1) Ingredients:
Dairy and non dairy ingredient:
{A} Dairy ingredient:
Include whole fresh milk, skimmed milk, milk powder, and concentrated
milk, fresh cream (source of both fat and solids – non- fat.
Function of milk fat:
1. imporove body and texture of ice cream.
2. Provides a rich flavor to ice cream.
3. Milk fat may be replace by vegetable fat of melting point below 37
C to avoid fatty mouth- feel
Function of milk solids–non-fats (SNF ):
1. Provides body texture and contributes to sweetness and air
incorporation.
{B} Non dairy ingredients:
{1} Sugar:
Sucrose or glucose , sorbitol
Function: Sweeting agent, decrease freezing point, improves texture
{2} Stabilizers:(Gelatine, agar agar, gum, carboxy methyl cellulose, sodium
alginate).

Function: combined with the water gel formation
Improve mix viscosity, air incorporation, texture and melting qualities
and prevent the formation of large ice crystals
{3} Emulsifiers: (egg yolk, whole egg, mono or diglycerides)
Function: dispersion of the fat throughout the mixture so prevent churning during
freezing, improve whipping quality and texture.
{4} Flavoring agent: (vanilla, chocolate, fruit, fruit juice, nut etc..)
{5} colouring matter: It improves appearance and reinforces flavours.
{6} Cornflouer or custard.


Manufacture of ice cream


On large scale
1. Ingredients:
Select ingredient of superior quality.
2. Calculation of the mix of the ice cream which depends on:
Legal standard, preference of the consumer, need of the market and
economic consideration.
Adjust the fat to the sugar ratio to avoid fatty mouth- feel
Adjust the T.S to the water ratio to avoid both lactose crystal formation and
ice crystal formation.
3. Mix blending:
The ingredients are weighed and blended together to produce what is known as the
“ice cream mix”. Blending requires rapid agitation to incorporate powders, and
often high speed blenders are used.
In small-scale, Ingredients are blended in the pasteurization vat during
heating at LTLT using an agitator or in some cases, a blender-emulsifier to
facilitate dispersion and mixing of ingredients.

In large scale, it is necessary to blend the mix before heat treatment
(HTST or UHT) due to short exposure during heating.
Ingredients such as dried milk powder and gum cannot be used without
heating the mix.
4. Heat treatment :
The mix is then pasteurized. Pasteurization is the biological control point in
the system, designed for the destruction of pathogenic bacteria. In addition to
this very important function, pasteurization also reduces the number of
spoilage organisms such as psychrotrophs, and helps to hydrate some of the
components (proteins, stabilizers).
Both batch pasteurizers and continuous (HTST) methods are used.
Batch pasteurizers lead to more whey protein denaturation, which some
people feel gives a better body to the ice cream. In a batch pasteurization system,
blending of the proper ingredient amounts is done in large jacketed vats equipped
with some means of heating, usually steam or hot water. The product is then heated
in the vat to at least 69
oC (155 F) and held for 30 min to satisfy legal requirements
for pasteurization, necessary for the destruction of pathogenic bacteria. Various
time temperature combinations can be used. The heat treatment must be severe
enough to ensure destruction of pathogens and to reduce the bacterial count to a
maximum of 100,000 per gram. Following pasteurization, the mix is homogenized
by means of high pressures and then is passed across some type of heat exchanger
(plate or double or triple tube) for the purpose of cooling the mix to refrigerated
temperatures (4 C). Batch tanks are usually operated in tandem so that one is
holding while the other is being prepared. Automatic timers and valves ensure the
proper holding time has been met.
Continuous pasteurization is usually performed in a high temperature short
time (HTST) heat exchanger following blending of ingredients in a large, insulated
feed tank. Some preheating, to 30 to 40 C, is necessary for solubilization of the components.
5. Homogenization / Emulsification:
The mix is also homogenized, which forms the fat emulsion by breaking
down or reducing the size of the fat globules found in milk or cream to less than 1
µm. Two stage homogenizations is usually preferred for ice cream mix. Clumping
or clustering of the fat is reduced thereby producing a thinner, more rapidly
whipped mix. Melt-down is also improved. Homogenization provides the
following functions in ice cream manufacture:
Reduces size of fat globules
Increases surface area
Forms membrane
makes possible the use of butter, frozen cream, etc.
By helping to form the fat structure, it also has the following indirect effects:
makes a smoother ice cream
gives a greater apparent richness and palatability
better air stability
increases resistance to melting
Homogenization of the mix should take place at the pasteurizing
temperature. The high temperature produces more efficient breaking up of the fat
globules at any given pressure and also reduces fat clumping and the tendency to
thick, heavy bodied mixes. No one pressure can be recommended that will give
satisfactory results under all conditions. The higher the fat and total solids in the
mix, the lower the pressure should be. If a two-stage homogenizer is used, a
pressure of 2000 – 2500 psi on the first stage and 500 – 1000 psi on the second
stage should be satisfactory under most conditions. Two stage homogenizations is
usually preferred for ice cream mix. Clumping or clustering of the fat is reduced
thereby producing a thinner, more rapidly whipped mix. Melt-down is also improved.
Homogenization is necessary in large plant producing ice cream of high
fat content and / or high overrun, but emulsification is an alternative in
small-scale operations where ice cream is of a relatively low fat content
and / or overrun.
Emulsified mix produce fat of larger size compared to homogenized
mix, of variable size of fat globules.
6. Cooling and ageing:
Rapidly cooling to 4 0C for 1.5 hours to stop the growth of M.Os, the mix is
then aged for at least four hours and usually overnight. This allows time for
the fat to cool down and crystallize, and for the proteins and polysaccharides
to fully hydrate. Aging provides the following functions:
Improves whipping qualities of mix and body and texture of ice cream
It does so by:
providing time for fat crystallization, so the fat can partially coalesce;
allowing time for full protein and stabilizer hydration and a resulting slight
viscosity increase;
allowing time for membrane rearrangement and protein/emulsifier
interaction, as emulsifiers displace proteins from the fat globule surface,
which allows for a reduction in stabilization of the fat globules and enhanced
partial coalescence.
Aging is performed in insulated or refrigerated storage tanks, silos, etc. Mix
temperature should be maintained as low as possible without freezing, at or below
5 C. An aging time of overnight is likely to give best results under average plant
conditions. A “green” or unaged mix is usually quickly detected at the freezer.
Cooling the mix to – 1 0C to 2 0 C permits the use of shorter ageing periods.

7. Freezing: Two stages
a)
In the first stage the temperature is reduced to be – 9 to – 10 0C accompanied
with air incorporation to increase the volume of the product up to 100% and may
be 120%, this process called
Overrun . Overrun may be calculated either by
volume or weight according to the following:
By volume:
% Overrun = (Vol. of ice cream – Vol. of mix used)/Vol. of mix used x 100%
Example : 500 L mix gives 980 L ice cream, (980 – 500)/500 x 100% = 96%
Overrun
80 L mix plus 10 L chocolate syrup gives 170 L chocolate ice cream, (Note : any
flavours added such as this chocolate syrup which become homogeneous with the
mix can incorporate air and are thus accounted for in this way : (170 – (80 +
10))/(80 + 10) x 100% = 88.8% Overrun
By weight:
% Overrun = (Wt. of mix – Wt. of same vol. of ice cream )/Wt. of same vol. of ice
cream x 100%
Must know density of mix (wt. of 1 L), usually 1.09 – 1.1 kg. /L.
Example : If 1 L of ice cream weighs 560 g, % Overrun = (1090 – 560)/560 x
100% = 94.6% Overrun
b) The second stage (hardening) , which is much slower, involves no incorporation
of air and takes place in a hardening room at – 20 to – 25
0C. for 10-12hrs, or
hardening at – 30 to – 35
0C for 2-5hrs.
(H) Finishing and packaging:
After hardening process the ice cream may be finished by enrobing with
chocolate or another candy product, by addition of chopped nuts etc., or by
combining the ice cream with water ice. Where necessary the ice cream is
then packaged.

(I) Storage and distribution:
Best temp of –13 to – 18 0C are used during transport and short-term display,
while a temperature of – 20 to – 25
0C is used for long-term storage.
Avoid fluctuation of temp during storage to avoid large crystal formation.
(B) At home:
Milk, sugars, flavouring and custard should be mixed in cooled water and
frozen the mixture with mixing to prevent formation of crystals.
(C) On small-scale (small vendors):
The milk added gradually to a starchy material to form a paste.
The remaining milk is added and mixed. Sugar is added and the mixture is left
to cool overnight. This period may allow multiplication of pathogenic
organisms, if present.
After cooling, flavour extract is added and the mixture is frozen by freezing
mixture (ice and salt) using hand-operating freezer or using their hands or
rotatory machine for rotating the mixture.
Types of ice cream
1- Ice cream:
2- Milk ice:
As ice cream but contains 2.5 – 3 % fat.
3- Custard ice cream:
They are made with eggs or egg yolk solids and must contain at least 1.4
% (w/w) egg yolk solids.
4- Water ice:
It is made from dilute fruit juice with sugar and added acid. Stabilizer and
added colours and flavours may also, be present.

5- Sherberts and Sorbets: They are both similar to water ice, but contain small
quantities of milk solids and in some cases whipping agents to give a higher
overrun.
6- Mousse:
It is a frozen confection of whipped cream, sugar and flavor with high fat
content.
7- Soft ice cream:
a frozen product served directly to the consumer at – 6.7 0C, sugar 2-3%.
8- Dietetic ice cream:
Ice cream of low sodium content for cardiac patient and using sorbitol
instead of sucrose.
9- Diabetic ice cream: Low lactose non-fat dry milk may be used (36 %), ,
sorbitol instead of sucrose.
10- Mellorine: Using vegetable fat instead of milk fat have similar melting point.
Microbiology of ice cream
Salmonella species and Listeria monocytogenes are main organisms that
contaminate ice cream which may be derived from contaminated fruits or
gelatin or eggs that used in the manufacture of ice cream.
Defects of ice cream
The defects in ice cream commonly are:
1) Off – flavour:
1- Cooked: Caused by using milk products heated to too high temperature
or by using excessively high temperatures in mix pasteurization.
2- High Acid: Use of dairy products with high acidity (usually due to
bacterial spoilage) or holding mix too long and at too high a temperature
before freezing.

3- Egg: Caused by using too much egg in an ice cream that is not specified
as a custard ice cream.
4- Salty: Ice cream too high in milk solids-not-fat. Too much salt may have
been added to the mix. using salted butter used instead of sweet butter.
5- Oxidized: Caused by oxidation of the fat or lipid material such as
phospholipid, similar to fluid milk oxidation. Induced by the presence of
copper or iron in the mix or from the milk itself.
6- Rancid: Caused by rancidity of milk fat. May be due to use of rancid
dairy products or due to insufficient heat before homogenization of mix.
(2) Body and texture defects:
1- Coarse/Icy Texture: Due to the presence of ice crystals of large size which
2- Gummy(Sticky) Body
3- Sandiness (Crystallization of lactose): One of the most objectionable
texture defects but easiest to detect. It is caused by Lactose crystals, which
do not dissolve readily and produce a rough or gritty sensation in the mouth.
This can be distinguished from “iciness” because the lactose crystals do not
melt in your mouth. Caused due to
Slow cooling
Increase solid non fat more than 11%.
Fluctuation of temperature
4- Weak Body
5- Crumbly Body


(3) Colour defects

Read also Table Butter and Cooking Butter

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