Module 11. Dried milks: history and status in India and abroad

Lesson 25


25.1 Introduction

Dry milk production has become an increasingly important segment of the dairy industry which is expected to grow further because of its features such as better keeping quality, less storage space, and lower transportation costs which result in attractive economics. Nonfat dry milk serves the same purpose for milk solids-not-fat that traditionally butter has done for milk fat. The ultimate aim of the industry is to obtain dry products which if recombined with water give little or no evidence of detrimental change compared to the original liquid product. Various names have been applied to the same dry milk product. For example, nonfat dry milk also has been called skim milk powder, dried skim milk, nonfat dry milk solids, and dehydrated skim milk. Dry whole milk, dry cream, dry buttermilk, and others frequently are called dried or powdered whole milk, etc., according to their identities.

25.2 History of Dried Milks

Dry milk has been known in some parts of the world for many centuries.

  • Marco Polo in the 13th century reported that soldiers of Kublai Khan carried a dried milk on excursions. The belief is that part of the fat was removed from the milk before drying and dehydration was accomplished by solar heating.
  • The first usable commercial production of dried milk was invented by the Russian chemist M. Dirchoff in 1832.
  • In 1855 T.S. Grimwade took a patent on a dried milk procedure, though William Newton had patented a vacuum drying process as early as 1837.
  • In 1909, Nicholas Appert, a Frenchman, developed dried milk in tablet form by air-drying of milk solids concentrated to a “dough” consistency.
  • During the last half of the 19th century, attempts to produce a dried milk involved the addition of other dry products to concentrated milk. Sugar, cereal products, and sodas, singly or in combinations, were added.
  • In 1850, Birdseye concentrated milk with added sugar until a solid was obtained.
  • A British patent was granted in 1855 to Grimwade who developed a modified dry product from highly concentrated milk to which sodium (or potassium) carbonate and sugar were added. This semi-solid material was extruded into thin streams and dried in trays.
  • Others who pioneered in methods of moisture removal from milk were Heine, Newton, Horsford, Dalson, Gallois and Deauve.
  • Patents and reports which emphasized processes for dry milk manufacture without the addition of other products began about 1898.
  • In 1901, Campbell of the United States and Wimmer of Denmark dried concentrated milk on trays.
  • In 1902, Hall obtained a patent on a new system of manufacturing dry condensed milk.
  • Today, powdered milk is usually made by spray drying nonfat skim milk, whole milk, buttermilk or whey. Alternatively, the milk can be dried by drum drying. Another process is freeze drying, which preserves many nutrients in milk, compared to drum drying.

25.3 Objectives and Requirements of Milk Powders

1. The main purpose of the manufacture of milk powder is to convert the liquid perishable raw material to a product that can be stored without substantial loss of quality, preferably for some years. Decrease in quality mainly concerns formation of gluey and tallowy flavors due to Maillard reactions and autoxidation, respectively and decreasing nutritive value especially decrease in available lysine. If the water content becomes very high and the storage temperature is high, caking due to lactose crystallization and enzymic and even microbial deterioration can occur. However, such problems can be avoided.

2. The powder should be easy to handle. It should not dust too much or be overly voluminous. It should be free-flowing, i.e., flow readily from an opening, and not stick to the walls of vessels and machinery. The latter requirement is especially important for powder used in coffee machines, etc.

3. After adding water the powder should be reconstituted completely and readily to a homogeneous mixture, similar in composition to the original product. Complete reconstitution means that no undissolved pieces or flakes are left and that neither butter grains nor oil droplets appear on top of the solution. ‘Readily reconstituted’ means that during mixing of powder and water no lumps are formed, because these are hard to dissolve. In the ideal situation the powder will disperse rapidly when scattered on cold water; this is called instant powder . Special processing steps are needed to achieve this property.

4. According to its intended use, the reconstituted product should meet specific requirements. If the use is beverage milk, the absence of a cooked flavor is of importance. If the powder is to be used for cheese making, the milk should have good clotting properties. If used to make recombined evaporated milk, satisfactory heat stability is necessary. So there are several widely divergent requirements that cannot be reconciled in one powder. For instance, it is not possible to make whole milk powder that has no cooked flavor and at the same time develops no oxidized flavor during storage. With respect to the intensity of the heat treatment, milk powders are classified as low-, medium-, or high-heat.

5. The product must be free of health hazards, be it toxic substances or pathogenic organisms. Besides general hygienic measures and checks prevailing in the dairy industry, there are some specific considerations.

The approximate composition of some types of powder is given in Table 25.1. There are other kinds of powders also. All of these products have specific requirements. Because the composition of the raw material varies, the composition of powders also varies. Accordingly, one has to tolerate a certain margin. This offers the possibility for adulteration; for instance, buttermilk powder or whey powder can be added to (skim) milk powder. The presence of a foreign powder can mostly be detected microscopically, but admixture of a small percentage of another liquid before the drying generally cannot so easily be established. Because whey is cheaper than skim milk, this kind of ‘adulteration’ sometimes occurs.

Table 25.1 Approximate composition (%w/w() of some types of powder

25.3.1 Uses

Milk Powder is a manufactured dairy product made by evaporating milk to dryness. An array of milk powders is now available. They are shown in Table 25.2 below

Table 25.2 Different types of milk powders available in market

  • Miscellaneous products that have been processed experimentally or commercially in small amounts are: dry creamed cottage cheese, dry butter, and dry yogurt. Modified equipment and special methods may be required for their successful manufacture.
  • Milk Powder is frequently used in the manufacture of infant formula, confectionery such as chocolate and caramel candy, and in recipes for baked goods where adding liquid milk would render the product too thin.
  • Powdered milk is also widely used in various sweets.
  • Milk Powder is also a common item in UN food aid supplies, fallout shelters, warehouses, and wherever fresh milk is not available.
  • It is widely used in many developing countries because of reduced transport and storage costs (reduced bulk and weight, no refrigerated vehicles). As with other dry foods, it is considered nonperishable, and is favored by survivalists, hikers, and others who require nonperishable, easy-to-prepare food.

Development of Drying Equipment

  • Drum / Roller Drier: Just (1902) was among the first inventors to receive patent rights on a drum drier with two rolls. Hatmaker of England improved Just's model. Vacuum drum driers were designed by Ekenbery, Sweeden 1839; Passburg (1903), Germany; and Govers (1909).
  • Spray Drier: Among the early inventors of spray drying equipment was Percy, who in 1872 combined atomization of a fluid and heated air. Stauf, a German, received a US patent on an improved design based on this principle in 1901.

25.5 Improvement of Reconstitutability / Aggomeration

As a result of pioneering research to improve the reconstitutability of nonfat dry milk in water, Peebles was issued patents in 1936, 1955, and 1958. In the Peebles method, regular spray dried milks (usually nonfat dry milk) are reprocessed by rewetting the surface of the particles in turbulent air which causes the wetted particles to collide, forming clusters. In the next stage, the moisture content is reduced with hot air. Products treated by this system became known as an "instantized" product. Instantized nonfat dry milk from the Peebles process appeared for general distribution on the retail markets in 1954.

25.6 Foam Spray System

The US Department of Agriculture's foam spray drying technique is an important contribution to the industry. Besides providing the advantage of one step processing, the method is more satisfactory for products sensitive to heat damage during dehydration. Foam spray dried dairy products have very good dispersibility, but poor sinkability.

25.7 Nutritional Value

  • Milk powders contain all standard amino acids - the building blocks of proteins - and are high in soluble vitamins and minerals.
  • According to USAID the typical average amounts of major nutrients in the un-reconstituted milk powder are: 36% protein, 52% carbohydrates (predominantly lactose), 1.3% calcium, 1.8% potassium (by weight). Storage of powder at high relative humidity and high ambient temperature can significantly degrade the nutritive value of milk powder.
  • Commercial milk powders are reported to contain oxysterols (oxidized cholesterol) in higher amounts than in fresh milk (up to 30μg/g, versus trace amounts in fresh milk). The oxysterol free radicals have been suspected of being initiators of atherosclerotic plaques.
  • Adulteration can occur in powders, e.g. melamine adulterant in infant formula, added to show higher protein content.

25.8 World Market

Milk powders are next to ghee and butter in market size. Some years back milk powders had a larger market size than that for butter. Due to relatively slow growth, the market for milk powders has lagged behind. However, it has shown a consistent positive growth on a year to year basis.
Last modified: Monday, 22 October 2012, 6:31 AM