Method of manufacture of ice cream

METHOD OF MANUFACTURE OF ICE CREAM

Method of manufacture

Selection of ingredients

The selection of ingredients is without doubtthe most important factor in successful ice cream manufacture. A clean fresh creamy flavour of the ice cream can be secured only by the use of products, which have been carefully selected and handled. The selection of ingredients depend on

  • Availability of milk products
  • Perishability of the products
  • Convenience in handling
  • Effecton flavour body and texture of ice cream
  • Costand
  • Equipment available.

Ice cream ingredients may be grouped into dairyand nondairy products.

I. dairy products

  • Source of fat
    • Sweetcream: this is the most desirable concentrated source of fat for use in amix
    • Frozen cream
    • Plastic cream
    • Unsalted butter
    • Butter oil.
  • Source of milk-solids- not fat
    • Skimmilk
    • Skim milk powder-this is most frequently used in the spray dried or flaked form.
    • Condensed skim milk
    • Sweet cream buttermilk.
  • Sources of both fat and solids not fat
    • Wholemilk.
    • Wholemilk powder
    • Condensedwhole milk
    • Evaporatedmilk.

II.Non-dairy products

  • Sweetening agents
    • Canesugar or beet sugar.
    • Cornsugar (dextrose)
    • Cornsyrup solids (dextrose+maltose)
    • Cornsyrup
    • Invertsugar (glucose +fructose)
    • Saccharin.
  • Stabilizers
    • Gelatin-of animal origin .

It was one of the first of the commercial stabilizers and still used, its advantages lies in its ability to form a gel inthe mix during the aging periods as well as during the freezing process, andeven after the frozen product is placed in the hardening room its peculiar gelstricture and its great affinity for waste prevent the formation of large ice crystals in ice cream and contribute to the smoothness on texture and firmnessin body of the frozen product.

The amount of gelatin used depends on several factors such as the source of gelatin whether from calf, pork skin or bonematerials. Its gel structure is measured by bloom test.

Commonly gelatin is used at the rate of 0.25 to0.5 % for a 250 bloom gelatin. The ice-cream mix stabilized with gelatin usually requires about 4 hours of ageing to develop complete stabilizing properties, while other stabilizing materials do not require an ageingperiod.

  • Sodiumalginate – of vegetable origin . The basic stabilizing principle ‘algin’ is extracted from ocean kelp (seaweed) growing on the shores of California and in Japan. This product improves whipping ability andleaves a slightly cleaner flavour in the mouth. It dissolves properly only when added to the mix at about 68-71ºC. aslightly smaller amount is needed to produce the same stabilizing effect asgelatin.
  • Guargum –of Indian origin.
  • Carageenan
  • Agaragar:
  • Carboxymethyl cellulose
  • Pectin

Emulsifiers: They are substances which help to form emulsions.

Glycerol Mono Stearate (GMS).

Flavours

  • Vanilla-this is the most popular flavour all over the world. Vanilla flavouring isobtained from the perennial climbing plant Vanilla Planifolia Andrews, a memberof the orchid family, vanillin is the principal flavouring material. Thetypical vanilla flavours is developed by fermenting the bean.
  • Chocolate

Chocolateand cocoa rank second only to vanilla as flavoring of ice cream. They are obtained from cocoa beans, the fruit of the perennial tree The obroma cocoa, growing in such tropical regions as Mexico,Ghana, Brazil, Venezuela,Nigeria, Ecuador, The West Indies, AfricanGold Coast and The East Indies etc.

  • Strawberry
  • Pineapple
  • Lemon
  • Banana
  • Mango
  • Orange

Colour

  • Yellow
  • Green
  • Pink.

Egg solids

  • Egg yolk solids improve the whipping ability.

Fruits and nuts

  • Apple
  • Banana
  • Mango
  • Pineapple
  • Grape
  • Almond
  • Pistachio
  • Cashewnut
  • Walnut
  • Groundnut.

Figuring the mix 

  • Knowledge of calculation of ice cream mix is helpful in properly balancing the mix, inestablishing and maintaining a uniform quality and in producing ice cream that conforms to legal standards. Ice cream mix may be divided into two groups, namely simple and complex. Simple mixes require the least calculation and are made of ingredients, each of which supplies one constituent. Complex mixes are more difficult to calculate they include mixes where atleast, one constituent is obtained from two or moreproducts. Complex mixes require the useof the Pearson’s square, algebraic methods.
  • The calculations are simplified by first finding the weight of ingredients neededto make 100kg of the desired mix. With the algebraic method, symbols such as X,Y, Z is used to represent the weightsof dairy ingredients required for a 100 kg batch of mix. These symbols are then used in writing the three equations that express the weight of fat serum solids (SNF) and the total weight of dairy ingredients needed for 100kg of mix.

Making the mix

The order in which ingredients are added is as follows:

  • All liquid ingredients are placed in a jacketed vat provided with a power stirrer,and the agitation and heating started at once, the dry ingredients, including skim milk powder, sugar, and stabilizers are added while the liquid material isagitated before the temperature reaches 49ºC. Proper suspension to avoidlumpiness of the dry ingredients may be obtained by either mixing the drymaterials thoroughly with part of the sugar before slowly adding it to the liquid, or by sifting / slowly adding these substances to the liquid.
  • If gelatin is the stabilizer used, it is best added after it is thoroughly mixed with equal volume of sugar, and before the liquid material reaches 49ºC.Alternatively, it can be sprinkled on the surface of the cold liquid and allowed to soak before the mixture is heated or soaked in water and the mixture heated to completely dissolve the gelatin, which is usually added to warm(38-49ºC) mix.
  • If sodium alginate is used, it should not be added until the temperature of the liquid material has reached at least 66ºC. The dry Dariloid is not allowed tosoak but is stirred up with cold water and immediately dumped into the hot mix.
  • If butter, plastic cream, frozen cream, or other products are used, they should becut into small pieces and added after time has been given to allow for complete melting before the pasteurizing temperature is reached. With a few exceptions, colouring andflavouring materials are added when the mix is frozen.

Pasteurizationof mix

ThePurpose of Pasteurization are

  • Itrenders the mix completely free of pathogenic bacteria,
  • Itdissolves and helps to blend the ingredients of the mix.
  • Itimproves flavour,
  • Itimproves keeping quality, and it produces a more uniform products

TheISI specification for pasteurization temperature – time combination for icecream mix are as follows:

  • Batchsystem- 68.5ºC for not less than 30min.
  • HTSTmethod - 80 ºC for not less than 25 sec.

In batch system the heating and holding may be accomplished in the vat used formixing the ingredients.

Homogenization of mix

The main purpose of homogenization is to make a permanent and uniform suspension ofthe fat by reducing the size of the fat globules to a very small diameter,preferably not more than 2 microns.

The advantages of homogenisation are

  • It prevents fat separation during ageing.
  • Produces more uniform ice cream with a smoother texture.
  • Improves whipping ability
  • Shortens ageing period.
  • Decreases the risk of churning occurring in the freezer and
  • Leads to the use of slightly less stabilizer.
  • The mix is usually homogenized at temperature from 63 to 77º C at pressure of 2500to 3000 PSI with one valve, or 2,500 to 3000 PSI at the first stage and 500 PSIat the second stage will usually give good results for an average mix (with 3to 12% fat).

Cooling and ageing of mix.

  • Coolingthe mix immediately after homogenization to 0-5ºCis essential, after which itshould be held in ageing tanks until used. Ageing refers to holding the mix ata low temperature for a definite time before freezing. The ageing temperature should not exceed 5ºC. The ageing time under commercial conditions may range from 3 to 4 hours,except for sodium alginate which requires no ageing.

Ageing

  • Improvesthe body and texture of ice cream
  • Improvesthe whipping capacity
  • Increasesmaximum overrun
  • Increasesmelting resistance.

Freezing the mix

  • Freezingis one of the most important operations in the making of ice cream for upon it depends the quality, palatability and yield of the finished product.
  • The freezing process may be divided into two parts. The mix with theproper amount of colour and flavouring materials generally added at thefreezer, is quickly frozen while being agitated to incorporate air in such away as to produce and control the formation of small ice crystals which isnecessary to give smoothness in body and texture, palatability and satisfactory overrun in the finished product.
  • When ice cream is partially frozen to a certain consistency it is drawn from the freezer into packages and quickly transferred to cold storage rooms where thefreezing and hardening is completed without agitation.

Classification of freezers

  • Batch freezer: Horizontal position and direct expansiontype.
  • Continuous freezer: Horizontal position anddirect expansion type.
  • Soft serve freezer: Batch and automaticcontinuous freezer of the direct expansion type.

Importance of rapid freezing

  • Rapidfreezing is essential for a smooth product because ice crystals that are formedquickly are smaller than those formed slowly. Therefore it is desirable to freeze and draw the mix from the freezer inas short a time as possible. A continuous freezer accomplishes this in a few seconds, while batch freezertakes 6 to 10 minutes. Since thefreezing continues after the ice cream is placed in the hardening rooms, the ice crystal formed during the hardening period are larger because they areformed more slowly than in the freeze. For this reason it is desirable to freeze the ice cream as stiffly as possible and yet have it liquid enough to be able to draw it out of the freezer.

Factors influencing the freezing time

  • Mechanical:
  • Type of freezer
  • Condition of freezer walls and blades
  • Speed of dasher.
  • Temperature of refrigerant.
  • Velocity of refrigerant passing around the freezing chamber.
  • Overrundesired.
  • Temperatureat which ice cream is frozen.
  • Rateat which freezer is unloaded.
  • Characteristics of mix.
  • Composition of mix.
  • Freezingpoint of mix.
  • Acidityof the mix.
  • Kindof ingredients, particularly those carrying fat.
  • Methodsby which the mix is processed.
  • Kindand amount of flavouring materials added.
  • Changesoccurring during freezing of ice cream mix.
  • Thefunction of freezing process is to freeze a portion of the water of the mix andto incorporate air into the mix. Thisinvolves:
  • Loweringof temperature of the mix from the ageing temperature to the freezing point.
  • Freezinga portion of the water in the mix
  • Incorporatingair into the mix.

Cooling the ice cream from the temperature at which it is drawn from the freezer to hardening room temperature.

The temperature of mix, which is put into the freezer drops very rapidly, this process, takes less than a minute or two. Mean while the rapid agitation reduces the viscosity by partially destroying the gel structure and by breaking up the fat globule cluster. The gel structure may restore it self partially during the hardening process in the hardening room. The rapid agitation hastens incorporation of air into the mix.

When freezing point is reached the liquid water changes to ice crystals, whichappear on the mix. These ice crystalsare practically pure water in a solid form, and thus the sugar as well as theother solutes becomes more concentrated on the remaining liquid water.Increasing the concentration of these solutes slightly depresses the freezingpoint of the liquid portion, so that the temperature must be lowered before anymore ice crystals will form. Thus, infreezing ice cream, the freezing point is continually being lowered by the formation of ice crystals and while the temperature drops, more ice crystals are formed, increasing the concentration of sugar and other solutes in theremaining liquid water until the concentration is so great that further freezing will not occur, thus all the water dose not freeze even after long periods in the hardening room.

Thefirst phase of freezing process accounts for the freezing of 3 to 6 per cent the water, depending on the drawing temperature. The second phase i.e. hardening process, this account for the freezing another 23 to 57 per cent, depending on the drawingtemperature.

Batch freezing: the batch freezer consistsmainly of a freezing chamber and a dasher. The dasher consists of two parts viz., scraper blades and the beater,the dasher performs the followingfunctions:

Aidsin transmission of refrigeration by keeping the mix in continuous contact witthe freezer walls, scrape freezer walls free of ice crystals, beats in air,continually pushes mix forward, which is essential for unloading the freezer.

The freezing procedure in batch freezer consists of

  • Preparation of the freezer
    • The freezer parts should be inspected to ensure that they are clean and dry. Then they should be assembled in accordance with the instructions from the manufacturer. The freezer is sanitized by running hot water or chemical (chlorine) sanitizers.
  • Adding the mix
    • Itis always desirable that the temperature of the mix be below 5ºC when it geesinto the freezer. Colour and flavourings should be added only when some ice crystals have been formed. The total volume of the mix ,flavour, and colour should be about half the total capacity of the freezer chamber.
  • Freezing and incorporation of air
    • Themix should now run into the freezer, the dasher should be started and then the refrigerant turned into the freezing chamber. This sequence must be maintained, the dasher must never be operated whenthere is no mix in the freezer. Neither should the refrigerant be turned on unless the dasher is in motion.
  • Drawing of ice cream
    • Whenice cream is drawn from the freezer, it should be sufficiently stiff to‘ribbon’ or almost hold its shape, and yet soft enough to ‘settle’ or lose itsshape within a minute or two. Thecontainer or package into which the ice cream is drawn should be cooledsufficiently to prevent the ice cream melting; this melting may cause a coarseand icy texture around the edge of the package and also loss of overrun. Formation of air pockets within the container should be avoided, the freezer should emptied rapidly to prevent wide fluctuations in overrun in the package, Therefore avoid filling small packages directly from the batch freezer,
  • Continuous freezing
    • Continuousfreezers are of two types in the market
    • One of these has two pumps just behind the freezer barrel; one pump pulls the mixfrom the supply tank and pumps it to the second one. The second pump operated at a speed approximately twice as great as that of the first pump. This has the effect of creating a partial vacuum between the two pumps. The valvedevice in the piping between the pumps allows for air to be sucked in. The amount of air incorporated can be regulated very accurately. The second pump pumps the mix and air into the freezer barrel. As the mix freezes, semi-frozen ice cream isforced out form the front of the machine.
    • The second type operated in a very similar fashion as the first, however here the two pumps are at the front. One pump pushes the mix into rear end of the freezer and the other helps to pull out thesemi frozen ice cream form the freezer. There is separate air pump that forces air directly into the freezer barrel. This second kind of continuous freezer is just as versatile as first one.

Some important advantages of the continuous freezing method are

  • Less stabilizer is needed.
  • A shorter ageing period.
  • Less flavouring material is needed.
  • Smoother ice cream is obtained.
  • Tendency towards development of sandiness decreases
  • A more uniform yield is obtained with less variation between packages.

Some disadvantages are

  • Great care must be taken in handling the parts of the machine that fit with verysmall clearance. Operators and mechanicsmust have special experience and training in order to avoid operational difficulties and possible damage to the equipment.
  • Itis difficult to prevent excessive overrun.
  • Thereis greater tendency for ice cream to shrink on volume after hardening.
  • Initialcost of the equipment is high.

Overrun in ice cream

Overrunis usually defined as the volume of ice cream obtained in excess of the volumeof the mix. It is usually expressed as apercentage. This increased volume iscomposed mainly of the air incorporated during the freezing process. The amountof air incorporated depends on the composition of the mix and the way it isprocessed; and is regulated so as to give that percentage overrun or yieldwhich will give the proper body, texture and palatability necessary to a goodquality product. Too much air willproduce a snowy, fluffy, unpalatable ice cream while too little, a soggy, heavy product. The desirable overrun percentage in different ice creams is given below.

Product

%OR.

Ice cream packaged

70-80

Ice-cream bulk

90-100

Softy ice cerium

30-50.

Thereare two basic or fundamental methods of calculating percentage overrun, viz.,by volume and by weight.

[(volumeof ice cream) –(volume of mix) /volume of mix ] i) % O R = x 100.  

(weight of unit volume of mix weight of unit volume of ice cream / weightof unit volume of ice cream )  ii) %O R = x100

Last modified: Monday, 16 April 2012, 10:56 AM