In this article we will discuss about process of manufacturing, packaging and storing dried milk products. Learn about the manufacture of: 1. Buttermilk Powder 2. Whey Powder 3. Cream Powder 4. Butter Powder 5. Ice Cream Mix Powder 6. Chhana Powder 7. Khoa Powder 8. Malted Milk Powder 9. Dried (Infant) Milk Food.
Method of Manufacture of Buttermilk Powder:
(i) From Sweet Buttermilk:
The method of manufacture by either the spray or drum process is similar to that of skim milk powder. The buttermilk should be cooled immediately to 5°C (40°F) on drainage from the churn, and stored in stainless steel lined tanks when intended for human consumption.
A common practice is to pre-heat it to 32-49°C (90-120°F) and separate it, so as to reclaim a portion of the fat. The pre-heating is then continued to 85°C (185°F) for 15 minutes. Then it is condensed to 16 per cent of the total solids for the drum process or 40-45 per cent for the spray process. The concentrate is re-heated to 71-79°C (160-175°F) and dried to a moisture content of 3 to 4 per cent.
(ii) From Sour (Ripened-Cream) Buttermilk:
In developed dairying countries, since the dried product is used for animal and poultry feeding, the question of the solubility of the finished product does not arise. Hence the buttermilk is dried by means of the atmospheric drum dryer, which requires the least initial investment and is simple to operate.
However, a few drying difficulties and storage problems are encountered:
1. Because of the high acidity, the concentrate tends to form an unmanageable smear on the drying drums.
2. The buttermilk, liquid or concentrate, constantly tends to whey-off, dropping its curd to the bottom of the container. (This tendency to whey-off increases when the buttermilk is heated preparatory to drying; and when it reaches the hot drying drum without the curd, it produces an abnormally thin film.)
3. Due to the high lactose content (about 40 per cent), the dried powder readily absorbs moisture and becomes sticky and cakes due to the crystallization of amorphous lactose glass into a hard mass of α-lactose hydrate.
Note:
(i) The above drying difficulty can be minimized by neutralizing the sour buttermilk to about 0.2 per cent acidity, using calcium hydroxide as neutralizer.
(ii) The whey-off problem can be solved by vigorous agitation to ensure uniform distribution of the curd particles in the body of the buttermilk when it reaches the drying drums.
(iii) The caking problem can be prevented by: inducing copious pre-crystallization between dryer and grinder/sifter and drying to a low moisture content (below 5 per cent) and packaging in a dry atmosphere in air-tight moisture-proof containers.
(iii) From High-Acid Buttermilk:
Sweet buttermilk is pasteurized at 82°C/180°F for 16 seconds or longer and then concentrated to 30 per cent total solids. After lowering its temperature to 46°C (115°F), it is inoculated with 1-5 per cent lactobacillus bulgaricus and agitated during incubation to produce a smooth curd. (Homogenization after incubation at low pressure will achieve the same result.)
When the acidity has developed sufficiently, equivalent to 10-12 per cent in the dry product, the buttermilk, without preheating, is spray-dried to 3.5-4 per cent moisture. The dry product should be removed continuously, cooled immediately and sifted. Care should be taken to control the outlet drying air temperature, else there will be excessive browning and a high solubility index.
Packaging and Storage:
Dried buttermilk is usually packed in kraft paper bags with plastic (polythene) liners or in fibre drums with or without plastic liners. It is usually stored at room temperature.
Keeping Quality:
The storage life of sweet buttermilk powder is relatively short, e.g., 1 to 3 months. However, a few commercial samples have been reported to have a shelf-life of more than a year at room temperature.
Method of Manufacture of Whey Powder:
Both drum and spray processes are common. The drum drying of a whey concentrate may be complicated by the formation of a sticky mass. Numerous patents and methods have been reported for the spray drying of whey to obtain a non-caking flowable product. One such spray process may be described as follows- the whey is passed through a separator to reclaim the fat, unless it is derived from skim milk.
The separated whey, with or without neutralization, is pre-heated to 77-104°C (170-220°F) and then condensed in a multiple-effect evaporator to 40-70 per cent total solids. The whey concentrate is cooled to 2-27°C (35- 80°F), seeded with lactose and then held for 24 hours for lactose crystallization. It is then spray-dried by the usual technique employed for skim milk powder.
Note:
Whey for animal feed can be drum or spray-dried by mixing 15-50 per cent skim milk, buttermilk or certain cereal products, e.g., wheat bran, which reduces the problem of a high lactose content. The procedure is similar to that for drum- dried skim milk.
Packaging and Storage:
Dry whey is usually packed in conventional bags with polythene liners. Since lactose in the amorphous form is very hygroscopic, the liner of the bag must be reasonably impervious to moisture vapours. Methods of production that cause a maximum degree of lactose crystallization reduce the tendency of dry whey to cake in storage, which is usually at room temperature.
Keeping Quality:
When stored at 10-15°C in air-tight polythene bags, the shelf-life is usually 6 to 12 months.
Method of Manufacture of Cream Powder:
Good quality cream is standardized to a ratio of fat: solids-not-fat of 1: 1. The cream is pasteurized at 74°C (165°F) for 16 seconds and homogenized at 3000 psi. It is then concentrated to 40-50 per cent total solids, re-heated to 65-71°C (150-160°F) and spray-dried to 1-2 per cent moisture.
The outlet air temperature is lower than that used for drying skim milk powder. (An alternate procedure consists of pre-heating the skim milk, concentrating it and adding pasteurized, homogenized cream; homogenization may be done at 65°C (150°F) using a pressure of 2000 psi in the first stage and 700 psi in the second stage. Re-heating and spray-drying follow.)
Note:
Dry cream has a tendency to stick to the sides of the drying chamber. Immediate continuous removal and cooling of the dried product is certain to result in a better product. During removal, rubbing action should be kept to a minimum, especially when the dry cream is hot, i.e., when the fat is in the liquid state.
The rubbing will cause the melted fat to ‘oil off’ and become free fat; the free fat in the dry product increases stickiness during handling and produces a greasy body and texture; also, a greater quantity of the product is lost, and lumpiness causes problems.
Packaging and Storage:
Normally dried cream is packed in bags with polythene liners or in fibre drums with or without a polythene liner, preferably small in size. It may be stored at room temperature or in a cooled room (10-15°C/50-60°F) with or without gas-packing. Oxidized flavour development and lumpiness are the main storage problems.
Keeping Quality:
At room temperature, the storage life of air-packed dry cream is limited to 2-3 months. However, gas packing increases the shelf-life considerably; oxidation is delayed by 12 months or more when stored at 32°C (90°F) with not more than 0.75 per cent oxygen in the package.
Storage of dry cream below the melting point of fat is certain to reduce lumpiness, while storage at 10-15°C is certain to reduce oxidative changes and thereby considerably prolong its keeping quality, especially when gas- packed.
Method of Manufacture of Butter Powder:
The following ingredients are used in the quantities mentioned:
During production, pasteurized cream is separated to 62 per cent fat. Sodium citrate is dissolved in the cream and the product is homogenized at 43°C (110°F) and 1000 psi in the first stage and 500 psi in the second. High grade casein is dispersed in skim milk at 65-82°C (150-180°F) and sodium hydroxide added slowly.
Glycerol mono-stearate (GMS) is melted and the anti-oxidant butylated hydroxy anisole (BHA) added. The mixture is blended into the caseinate solution. This is added to the cream solids. After heating it to 65°C (150°F), the product is spray-dried, cooled immediately and dry-blended with a free-flowing agent composed of 80 per cent sodium aluminium silicate and 20 per cent calcium phosphate.
Packaging and Storage:
Normally butter powder is packed in bags with polythene liners or in fibre drums with or without polythene liners, preferably small in size. It may be stored at room temperature or in a cooled room (10-15°C/50-60°F), with or without gas-packing.
Keeping Quality:
Air-packed butter powder is expected to have a storage life of 2-3 months at room temperature. However, a combination of gas-packing (with a low oxygen level in the package) and low temperature storage (10-15°C) is expected to raise the shelf-life to 6 months or more. Fat oxidation is the chief storage defect.
Method of Manufacture Ice Cream Mix Powder:
The ice cream mix is prepared in the usual manner by proper selection of ingredients; the percentages of fat and serum solids (milk-solids-not-fat), sugar, stabilizer and emulsifier, and total solids, are standardized to ensure proper composition of the dry product; the mix is made, pre-heated to 65-71°C (150-168°F) and homogenized at 2500 psi in the first stage and 500 psi in the second. The prepared mix is heated to 82-88°C (180-190°F) for 5-10 minutes, spray-dried to a coarse particle with 2- 2.5 per cent moisture, cooled at once to 32-38°C (90-100°F), sifted and packaged.
Note:
(i) Sugar used in preparing the ice cream mix is mainly sucrose, although 1-25 per cent may be replaced with corn syrup solids or dextrose. The product may be dried with 0-100 per cent of the required sugar, although usually 20 per cent of the required amount is added; the remaining percentage may be dry-blended in the form of a finely granulated sugar or the buyer may like to add the additional sugar himself,
(ii) Flavours are usually added when reconstituting the powder, and before freezing the mix.
Packaging and Storage:
Normally ice cream mix powder is packed in bags with polythene liners or in fibre drums with or without polythene liners, preferably small-sized. It may be stored at room temperature or in a cooled room (10-15°C/50-60°F) with or without gas-packing.
Keeping Quality:
Air-packed ice cream mix powder with not more than 2 per cent moisture is expected to have a storage life of 3- 4 months at room temperature. The product, when gas-packed with a 2 per cent oxygen level in the container, is expected to have a shelf-life of 6-12 months at 10-15°C. Browning, oxidation and staleness are common defects that develop during storage.
Method of Manufacture of Cheese Powder (Spray Drying):
Aged and medium- aged cheeses are selected by standard methods. These are cut and ground and then placed in a processing kettle, which consists of a steam-jacketed stainless steel vat equipped with a powerful agitator. Sufficient water at 27-32°C (80-90°F) is added to the vat to make a 35-40 per cent slurry.
Stabilizer (usually sodium citrate and/or disodium phosphate) is added at 1.5-2.5 per cent of the weight of cheese in the form of an aqueous solution. Cheese colour may be added to meet market demand. The addition of 0.5 per cent sodium chloride is optional. The cheese slurry is heated to pasteurization temperature and held for the required time (66°C/150°F for 2-5 minutes).
Thereafter the temperature is lowered to 60°C (140°F) and the product is homogenized at 1500-2500 psi during the first stage and 500 psi in the second. The cheese slurry is spray-dried to 2.5- 3.5 per cent moisture and the dry product is continuously removed from the drying chamber and immediately cooled to 29-32°C (85- 90°F).
Packaging and Storage:
Normally cheese powder is sifted through a 12-mesh screen prior to packaging in bags with polythene liners, or occasionally in fibre drums, with or without polythene liners, at room temperature or preferably at 10°C (50°F) 0° below.
Keeping Quality:
The keeping quality of dry cheddar cheese is relatively short. Air-packed cheddar cheese powder should be held at 10°C (50°F) or below to ensure longer storage life. Gas- packing with nitrogen, replacing the oxygen, will prolong the keeping quality. The addition of anti-oxidants also slightly delays oxidation.
Note:
One problem in the production of cheddar cheese powder is loss of cheese flavour from the product during spray drying. Reconstituted cheddar cheese with the same moisture content as the original cheese prior to dehydration is much milder in flavour.
Method of Manufacture of Chhana Powder:
Fresh cow milk, standardized to 4.0 per cent fat and filtered, is heated to first boil, preferably in a stainless steel jacketed steam-heated kettle of the rotary type, with constant stirring-cum-scraping to prevent the milk from scorching. The steam intake is then stopped. Sodium citrate at 0.02 per cent of milk is now added as an aqueous solution and thoroughly mixed into the milk, which is then covered and left undisturbed at 80 ± 2°C for 2±½ hours.
The milk is coagulated at about 70°C by the rapid addition of a 1-2 per cent lactic or citric acid solution till the whey is clear. (Alternatively, sour lactic-whey of similar acidity may be used as a coagulant.) The mixture of coagulated mass and whey is strained through a bleached muslin cloth, and the milk-solids (chhana) obtained are cooled to room temperature by submerging the chhana—tied with a cloth without being pressed, in the form of a bundle—in running cold water.
The chhana is deposited in a separate vessel and broken up into small particles, either manually or, better still, with a suitable mechanical device. Then a calculated amount of water is added to it so as to give 19-21 per cent total solids in the mixture. It is preheated to about 60°C and passed through a micro-pulverizer so as to give a smooth slurry.
This is pre-heated to 80 ± 5°C before spray drying under standard techniques, using an inlet air temperature of 195 ± 5°C and an outlet air temperature of 102 ± 2°C. The chhana powder is promptly removed from the drying chamber, cooled, packaged and stored at room temperature, preferably under gas- packing.
Packaging and Storage:
Chhana powder may be packaged in paper bags with polythene liners or fibre drums with or without polythene liners, with or without gas-packing, for storage at room temperature.
Keeping Quality:
Dried chhana appears to have a marketable life at room-temperature storage of 2 and 4 months under air-tight and gas-packed conditions, respectively.
Method of Manufacture of Khoa Powder:
Fresh, sweet buffalo milk, standardized to 5 per cent fat and filtered, is pre-heated to 65-70°C and homogenized at 2500 psi. It is then subjected to heat-dehydration as in the normal khoa-making process up to the stage when the heat- coagulation of milk-proteins is just completed.
A calculated amount of water is now added, so as to yield 16-18 per cent total solids in the mixture. This is pre-heated to about 60°C and passed through a micro-pulverizer to make it smooth. The slurry is now drum-dried under standard techniques with a steam pressure (inside the drum) of 50 ± 5 psi.
When the drier is properly set for working, the powder is collected, ground as required, and packaged and stored at room temperature, with or without gas-packing.
Note:
Increasing the total solids in the slurry (for drum drying consistent with the physical properties of the dried product, with a view to improving the economics of the process, merits further study.
Packaging and Storage:
Khoa powder may be packaged in paper bags with polythene liners or fibre drums with or without polythene liners, with or without gas-packing, for storage at room temperature.
Keeping Quality:
Dried khoa seems to have a marketable life at room-temperature storage of 3 and 3½ months under air-tight and gas-packed conditions, respectively.
Method of Manufacture of Malted Milk Powder:
Principle:
The liquid, separated from a mash of ground bailey malt and wheat flour, is combined with whole milk in such a proportion and manner as to ensure not only full enzymic action of the malt extract but also the prescribed US standards in the final dehydrated product.
Flow Diagram:
Details:
Barley malt may be obtained in dry form from a company specializing in its production, or can be prepared by the factory making malted milk powder. Barley malt is crushed (run through a roller-type mill) and then steeped in a separate kettle in about six to seven times its weight of water at 32°C (90°F) for 30 minutes. The purpose of steeping is to put the enzymes (diastase, etc.) in solution.
Simultaneously, wheat flour, which is rich in protein content besides being a source of starch, is prepared for the mash in a separate kettle. It is mixed with approximately 1.3 times its weight of water and the mixture cooked at 93°C (200°F) for 2 hours to make a paste. Generally the ratio of barley malt to wheat flour is 2.5:1.
The barley malt and its steeping water and the cooled flour paste are then transferred to a large mashing kettle where they are mixed. The mixture is held at 45°C (113°F) for 30 minutes; then the temperature is raised gradually to 70°C (158°F) in 30 minutes and held at that level for 2 hours.
This mashing or enzymation process ensures the complete conversion of starch to maltose and dextrin, together with the breakdown of the wheat-proteins into simpler and more readily digestible compounds. The characteristic pleasant flavour of barley malt is conveyed to the liquid extract from the barley husk.
When the mashing or enzymation process is complete, the husks are allowed to settle and the liquid portion of the mash is discharged into a hot well. The residue in the enzymation kettle is washed with two rinsings of water which are also added to the wort in the hot well.
To this wort, which contains approximately 11 per cent cereal solids, is added a calculated amount of whole milk containing prescribed amounts of fat and solids-not-fat so as to meet the minimum US requirements in the finished malted milk.
The mixture is then forewarmed to 65°C (150°F) and condensed in a standard vacuum pan to approximately 68-70 per cent total solids. It is then dried either in a special vacuum pan or by means of a drum or spray drier. (At Hindustan Milk food Manufacturers Ltd., Nabha, tray drying of the condensed product under partial vacuum has been successfully used over the past decade and a half.)
Note:
Vacuum drum drying is used for a substantial amount of the commercial production of malted milk powder. However, the latest trend is to employ the foam spray-drying technique.
Packaging and Storage:
The finished product, if obtained as a porous firm mass (as in pan drying), is broken into chunks and manually removed. The chunks are milled and the malted milk powder is promptly packaged. Since freshly dried malted milk is very hygroscopic, the milling and packaging are carried out in an atmosphere of controlled low humidity. For packaging, glass bottles with screw-type metal lids, or some containers impervious to moisture, are used. The product is stored at room temperature.
Keeping Quality:
Malted milk powder, properly made and packed, can be depended upon for long keeping quality even at room temperatures. This is ascribed to a film or layer of gluten (provided by the wheat), sugars and salts, that protects the surface of the fat globules against the quality-deteriorating influence of contact with air.
Method of Manufacture of Dried (Infant) Milk Food (Amul):
Principle:
The successive steps in the production of Amul baby food are:
(i) Reduction of the fat content of buffalo milk to 2.5 per cent;
(ii) Addition of phosphate buffer salt to react with ionized calcium and thus reduce the curd tension of infant food;
(iii) addition of sugar (sucrose) so as to reduce the protein content to about 22 per cent and the fat content to about 18 per cent in the dried product;
(iv) Concentration;
(v) Homogenization;
(vi) Drying;
(vii) Fortification with amino-acids, vitamins and minerals, and
(viii) Packaging in tin-cans under inert gas (nitrogen).
Flow Diagram:
Details:
(i) Receiving Milk:
Only high grade raw milk is accepted and used.
(ii) Pre-Heating:
For efficient filtration/clarification, the milk is pre-healed to 35-40°C.
(iii) Filtration/Clarification:
To remove extraneous matter which would cause consumer complaints.
(iv) Chilling and Storage:
The milk is promptly cooled to 5°C or below and held at this temperature so as to preserve its quality.
(v) Standardization:
This is done with the initial milk so that the dried product conforms to legal standards. Generally the Fat: SNF ratio is kept at 1: 3,227 (Amul) and the standardized milk contains-Fat 2.9 to 3.05 per cent; SNF 9.6 per cent.
(vi) Addition of Ferrous Sulfate and Sugar:
Ferrous sulfate is added to provide iron for blood formation, while sugar (sucrose) is added to increase the palatability of infant food. (The aqueous solution of each is filtered before addition.)
(vii) Pre-Heating:
The milk is pre-heated to 80°C/No hold for efficient destruction of all pathogenic, and almost all other harmful, micro-organisms and enzymes, so as to make the finished product safe for infant feeding.
(viii) Condensing:
The milk is concentrated in a double effect evaporator to a total solids content of usually 25-30 per cent for roller drying and 43-48 per cent for spray drying.
(ix) Homogenization:
In order to obtain uniform fat dispersion and other advantages in the finished product, the concentrated milk is homogenized, using a pressure of 50 kg./sq. cm. during the first stage and 25 kg./sq. cm. during the second.
(x) Chilling and Storage:
In order to preserve the quality of the concentrate till it is dried, it is chilled to 5°C and held at this temperature. The pH of the concentrate is adjusted to 7.0 with sodium bicarbonate; disodium phosphate is also added, if required.
(xi) Pre-Heating:
The concentrate is pre-heated to 70°C before it is dried, so as to increase the capacity of the drier.
(xii) Drying:
Either the roller or spray process is used.
(xiii) Grinding and Sifting:
The roller-dried product has to be ground before it is sifted. A proper mesh-size screen is used for both processes.
(xiv) Fortification with Amino-Acids, Minerals and Vitamins:
The dried product is generally sucked up by vacuum in a silo, where it is mixed with the required amino-acids, minerals and vitamins in the correct proportions by a mechanical mixer.
(xv) Gas Packing:
Only after the Quality Control Laboratory approves the quality of the finished infant food, it is nitrogen-packed in properly labelled and pre-sterilized tin-cans under strict sanitary conditions, and immediately sealed with pre-sterilized lids.
(xvi) Storage:
The (dried) infant milk food is normally stored at room temperatures.
Keeping Quality:
Dried infant/baby milk food, properly made and packed, can be kept for a long time even at room temperatures.