Skelmersdale based, Yew Tree Dairy is about to complete the final stage of a massive upgrade of their factory which will include the installation and commissioning of a new state-of-the-art milk powder processing system.Read more
Dairy processing is the transformation of raw milk into processed milk and products. Dairy processing can benefit entire communities by generating employment opportunities in milk collection, transportation, processing, and marketing.
Dairy processing definition
Dairy processing definition = processing of raw milk (from cows, goats, buffaloes, sheep, horses, camels) for human consumption.
- Introduction to dairy powder
- Heat treatment and pasteurization
- Drying methods
- Milk powder manufacture
- Milk powder processing steps
- Innovation in milk powder technology
Dairy powders are manufactured dairy products made by means of drying or evaporation. One purpose of drying is to preserve it; dairy powders have a far longer shelf life than in liquid form and don’t have to be refrigerated, due to the low moisture content. Another purpose is volume reduction for transportation and storage convenience.
These are the two main types of industrial processes:
- Heat treatment to ensure the safety of milk for human consumption and to lengthen its shelf-life
- Dehydrating dairy products such as butter, hard cheese, and milk powders
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 numbers of spoiling microorganisms to levels at which they do not represent a significant health hazard.
The pasteurization process may vary from one country to another, according to their legislation.
Milk can be processed further to convert it into high-value, concentrated and easily transportable dairy products with long shelf-lives, such as butter, cheese, and ghee.
Many different types of products are prepared by dehydration nowadays using dryers that are in operation in different industries like chemical, food, pharmaceutical, process and dairy. Lowering the water content in bulk products can be achieved by 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.
Transforming a liquid product into a dry powder requires the removal of nearly all water, the amount of which often exceeds the weight of the final product.
During the water removal, the processed product is undergoing deep 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 method of water removal cannot be optimal throughout the whole process, as also the product composition is different from one food product to another.
In the dairy processing industry these dehydration methods have been largely adopted:
- Evaporation: concentrating milk of water-like viscosity to a concentrate.
- Spray drying transforming the concentrate into droplets and evaporating water from these droplets in order 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 from below, causing the powder particles to separate and behave rather 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, the use of 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 such items as 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 they receive 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
The conventional process for the production of 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.
The next milk powder processing step is “preheating” during which 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 is used to concentrate whole milk, skim milk, whey, whey protein concentrates and permeate from membrane filtration modules. Water is evaporated by means of indirect heating. Product and heating medium (steam) are kept separate from one another by means of a sheet of special steel. The heat released during the condensing of the steam is transferred to the product via the partition. Evaporation also constitutes the preliminary stage of the drying of the said products.
Spray drying involves atomizing the milk concentrate from the evaporator into fine droplets. This is done inside a large drying chamber in a flow of hot air (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 prior to atomization to reduce its viscosity and to increase the energy available for 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 in order 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 and to 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. A few hours at elevated temperatures (> 40°C) during transshipment can undo many weeks of careful storage.
Agglomerated milk powder
The manufacture of agglomerated milk powder initially follows the standard process of evaporation and drying.
However, during spray drying small particles (fines) of milk powder leaving the dryer are recovered in cyclones and returned to the drying chamber in the close proximity of 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 and 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 is optimized to a high extent.
The introduction of new milk powder technology will be the key. Optimization of single process units will have an influence on up- and downstream process units. Therefore, it is important to take the whole production chain into account.
The goal is to design an optimization routine which takes energy and water consumption, Lifecycle assessment (LCA) aspects, and economic aspects into account, resulting in a sustainable milk powder production chain.
Articles about Dairy Processing
As milk and dairy products are dried for supply chain convenience, powder aeration typically results in poor densification during bulk bag filling, creating instability of bags in storage.Read more
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