Dairy Processing

Heat treatment and pasteurization

Before heat treatment of milk products was adopted, milk was a source of infection, as it is an ideal growth medium for microorganisms.

Pasteurization is a heat treatment process that extends the usable life of milk and reduces the number of spoiling microorganisms to levels at which they do not represent a significant health hazard.

According to their legislation, the pasteurization process may vary from one country to another.

Milk can be processed further to convert into high-value, concentrated, and easily transportable dairy products with long shelf-lives, such as butter, cheese, and ghee.

Dehydration

Many different types of products are prepared by dehydration nowadays using dryers in operation in various industries like chemical, food, pharmaceutical, process, and dairy. Lowering the water content in bulk products can be achieved in different ways and means.

The process industry offers a wide variety of dryers, in which the correct selection is subject to the desired characteristics of the final product.

Drying methods

Transforming a liquid product into a dry powder requires removing nearly all water, the amount of which often exceeds the weight of the final product.

During the water removal, the processed product undergoes significant changes in physical structure and appearance, starting with thin water-like liquid and finishing with dry powder at the end of the process.

Therefore, one single water removal method cannot be optimal throughout the whole process, as the product composition is also different from one food product to another.

In the dairy processing industry, these dehydration methods have mainly been adopted:

• Evaporation: concentrating milk of water-like viscosity to a concentrate.
• Spray drying: transforming the concentrate into droplets and evaporating water from these droplets to get a powder that consists of dry particles.
• Fluid bed drying: Fluid bed drying is used for drying milk powder. Air is blown through the powder below, causing the powder particles to separate and behave somewhat like a fluid. Alternatively, a layer of fluid-like powder in which the particles are kept apart by an airflow.
• Drum drying in drum-drying the material is dried at relatively low temperatures over-rotating, high-capacity, steam-heated drums that produce sheets of drum-dried product. The water in the concentrate evaporates, and the vapor is drawn off. This product is milled to a finished flake or powder form. With the development of spray drying, drum drying to produce milk powder has been reduced.

Each drying method should be adjusted to the properties of the processed material at each processing step: the more difficult the product, the more complex the plant. Milk powder factory in New Zealand. Copyright: Fonterra

Milk powder manufacture

Milk powder manufacture is a simple process now carried out on a large scale. It involves the gentle removal of water at the lowest possible cost under stringent hygiene conditions while retaining all the desirable natural properties of the milk - color, flavor, solubility, nutritional value.

Powdered milk and dairy products include dry whole milk, skimmed dry milk, dry buttermilk, dry whey products, and dry dairy blends.

Milk powders may vary in their gross composition (milkfat, protein, lactose), the heat treatment during manufacture, powder particle size, and packaging.

Milk powders of various types are used in a wide variety of products such as baked goods, snacks and soups, chocolates and confectionary (e.g., milk chocolate), ice cream, infant formulae, nutritional products, et cetera.

Milk powder processing

Separation

The conventional process for producing milk powders starts with taking the raw milk received at the dairy factory and pasteurizing and separating it into skim milk and cream using a centrifugal cream separator.

Preheating

The successive milk powder processing step is "preheating," The standardized milk is heated to temperatures between 75 and 120 °C. Preheating causes a controlled denaturation of the whey proteins in the milk, and it destroys bacteria, inactivates enzymes, generates natural antioxidants, and imparts heat stability.

Evaporation

Evaporation is used to concentrate whole milk, skim milk, whey, whey protein concentrates and permeate from membrane filtration modules. Water is evaporated using indirect heating. Product and heating medium (steam) are kept separate from one another utilizing a special steel sheet. The heat released during the condensing of the moisture is transferred to the product via the partition. Evaporation also constitutes the preliminary stage of the drying of the said products.

Spray drying

Spray drying involves atomizing the milk concentrate from the evaporator into fine droplets. This is done inside a large drying chamber in a hot air flow (up to 200°C) using either a spinning disk atomizer or a series of high-pressure nozzles. The milk droplets are cooled by evaporation, and they never reach the temperature of the air. The concentrate may be heated before atomization to reduce its viscosity and increase the energy available for drying.

Secondary drying

Secondary drying takes place in a fluid bed or in a series of such beds, in which hot air is blown through a layer of fluidized powder removing water to give a product with a moisture content of 2-4%. Safety measures must be taken to prevent fires and to vent dust explosions should they occur in the drying chamber.

Packaging and storing of milk powder

Milk powders are immensely more stable than fresh milk, but protection from moisture, oxygen, light, and heat is needed to maintain their quality and shelf life. Milk powders readily take up moisture from the air, leading to a rapid loss of quality and caking or lumping.

Milk powder is packed into either plastic-lined multi-wall bags or bulk bins. Whole Milk Powders are often packed under nitrogen gas to protect the product from oxidation, maintain their flavor, and extend their keeping quality.

The packaging is chosen to provide a barrier to moisture, oxygen, and light. Bags generally consist of several layers to provide strength and the necessary barrier properties.

Shipments of milk powder should never suffer prolonged exposure to direct sunshine, especially in tropical countries. During transshipment, a few hours at elevated temperatures (> 40°C) can undo many weeks of careful storage.

Agglomerated milk powder

The manufacture of agglomerated milk powder initially follows the standard evaporation and drying process.

However, during spray drying, small particles (fines) of milk powder leaving the dryer are recovered in cyclones and returned to the drying chamber near the atomizer.

The wet concentrate droplets collide with the fines and stick together, forming larger irregular-shaped "agglomerates." Agglomerated milk powder disperses in water more rapidly and is less dusty and easier to handle than standard milk powder.

Milk powder technology and the environment

Large amounts of energy are consumed in milk powder technology, so milk powder manufacturing plants developed over the years have become increasingly more energy efficient.

Innovation in milk powder technology

Milk powder production involves many thermal processes, making it highly energy-consuming. In the past decades, the current production process has been significantly optimized.

The introduction of new milk powder technology will be the key. Optimization of single process units will influence up-and downstream process units. Therefore, it is crucial to take the whole production chain into account.

The goal is to design an optimization routine that takes energy and water consumption, Lifecycle assessment (LCA), and economic aspects into account, resulting in a sustainable milk powder production chain.