Thermization: A Gentle Heat Treatment for Preserving Raw Milk

Thermization is a mild heat treatment used in the dairy industry to improve the quality and storage life of raw milk before further processing. Unlike pasteurization, which is designed to eliminate harmful disease-causing bacteria, thermization applies a lower level of heat for a shorter period. The process typically heats raw milk to between 57°C and 68°C (135°F to 154°F) for 10 to 20 seconds, followed by immediate cooling to approximately 4°C (39°F). This gentle treatment reduces spoilage microorganisms while preserving the milk's natural flavor, nutritional qualities, and protein structure.

The thermization process is straightforward but carefully controlled. First, raw milk passes through a plate heat exchanger, where it is rapidly heated to approximately 63°C to 65°C. The milk is then held at this temperature for about 15 to 20 seconds, allowing sufficient time to reduce populations of spoilage bacteria. Immediately afterward, it is rapidly cooled to below 4°C, slowing any remaining microbial activity and preparing the milk for refrigerated storage or additional processing.

One of the primary purposes of thermization is to reduce the number of psychrotrophic bacteria, which are microorganisms capable of growing even under refrigeration. These bacteria produce enzymes that continue breaking down milk components during storage, causing undesirable flavors, odors, and texture changes. By lowering their numbers, thermization significantly slows milk deterioration and helps maintain freshness. Studies have shown that thermized milk can generally be stored below 8°C (46°F) for up to three days before further processing, provided proper refrigeration is maintained.

Another important advantage is the reduction of naturally occurring enzymes such as heat-sensitive lipases and proteases. These enzymes break down fats and proteins, leading to rancid flavors, bitterness, and reduced product quality over time. Thermization inactivates many of these heat-labile enzymes, helping preserve the milk's taste and extending its usable shelf life before pasteurization or manufacturing.

Because thermization uses lower temperatures than pasteurization, it causes minimal changes to the milk's natural composition. Valuable proteins, minerals, and much of the fresh flavor remain largely intact. This makes thermized milk especially suitable for specialty dairy products where maintaining raw or minimally processed characteristics is desirable.

Thermization is particularly valuable in cheesemaking. Many artisan and specialty cheeses require milk that retains much of its original protein structure and flavor profile. Thermized milk provides a practical compromise by reducing spoilage bacteria while preserving the characteristics needed for proper cheese ripening and flavor development. It also gives cheese producers greater flexibility by extending the storage time of raw milk before production begins.

It is important to note that thermization is not a substitute for pasteurization. While it effectively reduces spoilage microorganisms and improves storage stability, it does not eliminate all harmful pathogens. Consequently, thermized milk intended for drinking is usually pasteurized before reaching consumers. Instead, thermization serves as an intermediate preservation step that enhances milk quality, extends storage by approximately 24 to 72 hours, and supports efficient dairy processing while maintaining the fresh qualities of raw milk.
Thermization: A Gentle Heat Treatment for Preserving Raw Milk

Thermization vs. Pasteurization: Key Differences in Milk Safety and Quality

Thermization and pasteurization are both heat treatments aimed at improving milk's safety and shelf life, but they differ in approach and results. Here are the main distinctions:

Temperature and Duration:

• Thermization: Heats milk to a lower range of 57°C to 68°C for about 15 minutes.
• Pasteurization: Uses higher temperatures, typically:
  • Low-Temperature Long-Time (LTLT): 63°C for 30 minutes.
  • High-Temperature Short-Time (HTST): 72°C for 15 seconds.

Purpose:

• Thermization: Reduces spoilage bacteria while preserving the milk’s enzymes and flavors, often as a pre-treatment before pasteurization or further processing.
• Pasteurization: Eliminates pathogenic bacteria and reduces spoilage organisms to ensure milk is safe for consumption and has an extended shelf life.

Effect on Milk Quality:

• Thermization: Retains more of the milk's original taste, enzymes, and nutrients, making it ideal for high-quality cheese production.
• Pasteurization: Alters milk more noticeably, affecting flavor and nutritional content but provides greater safety by killing harmful pathogens.

Shelf Life:

• Thermization: Extends raw milk's shelf life by a few days, useful for short-term storage before further processing.
• Pasteurization: Extends milk's shelf life significantly, allowing for several weeks of refrigeration.

Regulatory Standards:

• Thermization: Often does not meet the regulatory safety requirements for commercial milk in many countries.
• Pasteurization: Universally accepted and mandated by health authorities to ensure milk safety.

In summary, while both methods enhance milk safety, pasteurization is more effective at eliminating pathogens and prolonging shelf life, whereas thermization focuses on preserving milk's natural qualities, especially for applications like cheese making.
Thermization vs. Pasteurization: Key Differences in Milk Safety and Quality

Evaporated milk: Definition and processing

Evaporated milk is made by heating raw milk in a partial vacuum so that the boiling point is raised to 43 - 60°C/110–140°F until it has lost about half its water. The resulting creamy, mildly caramel flavored liquid is then homogenized and then canned and sterilized.

Evaporated milk has a creamy consistence mildly caramel flavored liquid and it differs from ordinary milk in which containing slightly more than twice the number of solids.

It is then homogenized and then canned and sterilized. Evaporated milk is gaining popularity worldwide due to the long shelf life it enjoys. Evaporated milk does not require refrigeration if the can is not opened.

According to Codex Standard, evaporated milks are milk products which can be obtained by the partial removal of water from milk by heat, or by any other process which leads to a product of the same composition and characteristics.

It contains not less than 6.5 percent by weight of milk fat, not less than 16.5 percent by weight of milk solids not fat, and not less than 23 percent by weight of total milk solids.

Nicolas Appert was the first person to preserve milk in concentrated form in the early nineteenth century. First, he concentrated the milk by boiling it in a water bath over a fire, then poured it into glass bottles after cooling. Final process was sterilized the product by heating the bottles for 2 h in a boiling water bath.

The evaporation process involves evaporation, concentration, homogenization, and sterilization of whole milk. The process also concentrates the nutrients and the energy content of the evaporated milk.
Evaporated milk: Definition and processing

Milk and dairy foods

Milk is the secreted fluid of the mammary glands of female mammals. It contains nearly all the nutrients necessary to sustain life. Since the earliest times, mankind has used the milk of goats, sheep and cows as food. Milk is basically composed of water (~87 percent), milk fat (~4 percent) and non-fat solids (~9 percent).

In addition to milk, several dairy products such as cream, butter, yogurt, kefir, and cheese have been produced and consumed worldwide for millennia.

Fresh milk is highly perishable, bulky, and easily contaminated (it is a favorable medium for bacterial growth). Because it is so susceptible to contamination and adulteration (with water), fluid milk production, treatment and distribution is widely subject to controls.

Milk tastes mildly sweet, while its odor and flavor are normally quite faint. Cow milk generally contains between 3 and 4 g of fat/100 g, although values as high as 5.5 g/100 g have been reported in raw milk. Most milks consumed now contain a standardized fat content of around 3.5 g/100 g.

Milk fat occurs in the form of droplets or globules, surrounded by a membrane and emulsified in milk serum (also called whey). The fat globules (called cream) separate after prolonged storage or after centrifugation. The fat globules float on the skim milk. Homogenization of milk so finely divides and emulsifies the fat globules that cream separation does not occur even after prolonged standing.

The major proteins found in milk are casein and whey proteins, with casein (αs1-, αs2-, β-, and κ-casein) accounting for approximately 78 percent of the protein in cow milk and whey proteins accounting for about 17 percent of the total protein

Milk and dairy products are nutrient-dense foods, supplying energy and high-quality protein with a range of essential micronutrients (especially calcium, magnesium, potassium, zinc, and phosphorus) in an easily absorbed form. Milk minerals are crucial for human health and development as well as in dairy processes as cheese-making and for all traits involving salt-protein interactions.

In recent decades, technological advances have supported the development of new dairy-based products. Broadly, dairy products can be categorized as basic products, such as fermented milk, cheese and yoghurt, and value-added products, such as low-fat and fortified milks.

Milk can be internationally traded either in dry, evaporated or condensed whole milk form or as dry skimmed milk powder (NFDM). These whole milk products may be reconstituted to fluid milk by mixing with water. Skimmed milk powder is reconstituted by mixing with butteroil (anhydrous milk fat) or vegetable fats and water to obtain a mixture of about 3.5 to 4 percent fat and 9 percent non-fat-solids. Well-reconstituted milk is said to be practically indistinguishable from fresh milk.
Milk and dairy foods

Physical properties of milk

Physically, milk is a rather dilute emulsion combined with a colloidal dispersion in which the continuous phase is a solution.

Milk is a very complex fluid. It contains several hundred molecular species, mostly at trace levels.

Two physical phenomena are primarily responsible for the visual appearance of milk. First, milk is a protein-stabilized emulsion of fat in a continuous aqueous solution.

Secondly, milk is a suspension of insoluble colloidal mineral particles.

Milk is a white or yellow-white, opaque liquid. The color is influenced by scattering and absorption of light by milk fat globules and protein micelles. Therefore, skim milk also retains its white color.

A yellowish, i.e., yellow-green, color is derived from carotene (ingested primarily during pasture grazing) present in the fat phase and from riboflavin present in the aqueous phase.

The specific density of milk decreases with increasing fat content, and increases with increasing amounts of protein, milk sugar and salts.

The specific density of cow’s milk ranges from 1.029 to 1.039 (15 degree C). The density and specific gravity of milk vary somewhat with breed. Milk from Ayrshire cows has a mean specific gravity of 1.0317 while that of Jersey and Holstein milks in 1.0330.

Defatted (skim) milk has a higher specific density than whole milk. The freezing point of milk is -0.53 to -0.55 degree C. This rather constant value is a suitable test for detection of watering of milk.

Physical properties of liquid milk are measured by traditional methods that are included in the control of milk at receptions. Some of these properties are routinely controlled because they can give indirect information about alterations or adulterations of milk.
Physical properties of milk 

Filled Milk

Filled milk is a milk or cream to which a fat other than butter fat has been added. A typical milk consists of skim milk or nonfat dry milk to which a vegetable fat has been added.It’s cheaper and contains less cholesterol than whole milk.

The water phase contains milk solids. These solids usually give a good flavor background, which usually makes addition of a milk or cream flavor unnecessary.

Usually the protein ingredient comes from soybeans, through sometimes the soya proteins is combined with a chalky protein substance called sodium caseinate, which is derived from real milk.

It is a homogenized product and its fat content should not less than 3 per cent and SNF 8,5 per cent.

This product was very unpopular initially, the ‘Filled Milk Act’ was passed by the US Congress in 1923 to prohibit interstate and foreign shipments of such products.

Congress claimed that filled milk was unhealthy, and that it was manufactured to look like real milk, thus confusing consumers.

By 1970s, the drive to reduce the intake of cholesterol on the diet resulted in an increased demand for filled milk products.

Filled Milk