Homogenization of Milk: What It Means and How It Works

Milk is one of the richest sources of protein we need daily. Owing to this, it’s available in different forms and often undergoes different processes, one of which is the homogenization process of milk. In this article, we’ll explore what this process entails, its benefits, and the machines necessary to actualize it. Read on.

What Is Homogenization of Milk?

Homogenization of milk is an industrial process of breaking the fat molecules in the milk into thinner fragments that allow for easy mixing with other constituents of the milk, giving rise to a more homogeneous solution. Consequently, the milk because finer and can last longer than its unprocessed counterpart.

What Is the Purpose of Homogenization in Milk?

There are so many reasons why we may homogenize milk. But some of the purpose of homogenizing milk is to:

  • Keep it fresh for a longer period: Fresh or non-homogenized milk is prone to quick spoilage—it spoils within one or two weeks. Although all milk—homogenized or not—contains at least one bacteria capable of causing spoilage at certain temperatures. However, pasteurization before homogenization gives milk a longer shelf life. 
  • Improve its physiology: One of the benefits of homogenized milk is to improve the overall look, feel, and composition of milk. Homogenization breaks down the fat molecules, usually above 15 micrometers, into fine-grain molecules at less than 2 micrometers when seen through a microscope. 
  • Improve and maintain its richness: During homogenization, we pass the pasteurized milk solution through a high-pressure pump, usually between 35–350 Bar. After this process, the milk becomes thicker and whiter because of the blended liquid and fat components.
  • Use it to produce other milk products: Being one of the many processes of refining milk, homogenized milk can be further processed to get other forms of milk as well as by-products.

Benefits of Homogenized Milk

Here are some of the health and economic benefits to consider before homogenizing milk:

Easier digestion

This is arguably one of the best benefits of drinking homogenized milk. This easier digestion results from the significant reduction of fat globules. The reduced fat may now easily pass through our gut, sometimes unnoticed and other times acted upon by digestive enzymes.    

Better taste and flavor

When you want to get the best taste and flavor from milk, homogenizing it is a good step to take. The reason for this is not far from its blended components. Unlike untreated milk, we can uniformly add additives to homogenized milk.

Reusable

As said earlier, adding additives to homogenized milk is easier because the consistency in the milk makes it easier for the additives to blend without after-effects or sedimentation. This makes homogenized milk easily reusable and applicable to other food production processes like baking or making dairy products.

Appealing

Homogenized milk is generally yummier than non-homogenized milk. The blended fat adds more viscosity and denser white color to the milk. Also, the pasteurization contributes to the milk’s appealing flavor and texture.

Supplementing Nutrients

Supplementing nutrients is one of the benefits of homogenized milk for babies and toddlers. Fortified homogenized milk gives toddlers and children stronger bones and good eyesight because of vitamins A and D.

What Are Homogenizers?

Before discussing how to homogenize milk, it’s essential to know the most instrumental equipment used in the process—a homogenizer machine. A homogenizer machine, or homogenizer, is a laboratory or industrial mixer that forces milk through valves under pressure and low or high velocity. A valve comprises a valve seat and an impact ring. 

The valve seat is confined to increase the pressure when the piston pumps the milk from the inlet chamber. The impact ring supports the valve seat during this process. Usually, a pressure gauge or regulator controls the pressure in the piston. The higher the pressure, the smaller the fat globules will be. 

One of the core uses of milk homogenizers is to break down the fats through the valve. This turns the milk into a colloidal solution. A colloidal solution is a mixture comprising insoluble components suspended in a solution. For milk, it’s fat globules and proteins.

Types of Milk Homogenizers

We have homogenizers for various industries. However, the standard milk homogenizers you may find in factories include: 

High-Pressure Homogenizer

High-pressure homogenizers apply greater pressure to untreated milk solutions, usually between 35 and 350 bars. Their architecture comprises the inlet chamber, a slender or confined single-valve tapering into a double or triple-headed cylindrical pump, the discharge valve, and the hopper.

Low-Pressure Homogenizer

The low-pressure homogenizer is built with broader pipes with pistons, which increases the velocity of the milk passing through the orifices or valves; hence, the pressure drops drastically. 

Ultrasonic Vibrators

Ultrasonic vibrators (also called sonicators or sonic oscillators) depend on high-frequency vibration and hammering to break down fat globules in untreated or non-homogenized milk. 

What Is the Process of Homogenizing Milk?

Homogenizers require the pumping pressure of valves to homogenize and mix the milk solutions properly. In most cases, a single valve may be used. In other specific cases requiring decluttering of the milk solution, we may require two or more valves. 

With that being the case, the two-stage homogenization of milk is the single and double-stage homogenization. 

We call it single-stage homogenization, whenever only one valve is used to homogenize milk. However, if a single valve doesn’t do the job as expected, we’ll need to connect an extra valve—a low-pressure homogenizer—to support the previous stage. The extra valve or machine connected is called the double-stage homogenization.

The second valve operates at a lesser pressure than the first or single-stage homogenization. Usually, this pressure is between 25 and 35 bars so as not to alter fat globules and change the milk’s chemistry and physiology.

If the double-stage homogenization doesn’t do the job, more valve systems can be added subsequently to streamline milk homogenization or production.

Operating a Homogenizing Machine

To successfully perform homogenization of milk, understanding how to operate or set up a homogenizer is essential. Abiding by the following practices streamlines the process:

Before Operation

Before starting up the machine, some activities and checks you must do include:

  • Use water to lubricate and heat the machine for five minutes. This technique flushes previous residues that may be contaminated. Additionally, you can test if the machine functions properly before regular operations.
  • Check if there is any leakage in the machine. You can check the valves, including the valve seat and the impact ring.
  • Check the machine’s pressure controls, idlers, and oil pressure. Importantly, the oil pressure must be at least 0.98 Bar. If not, the machine might shut down strangely.

During Operation

After testing the machine and ensuring everything is in perfect condition, you may power the machine properly.

  • Start the motor and fill the valve with adequate milk, adjusting the multiport valve as you do so.
  • Check the pressure gauge and adjust the pressure accordingly while the machine operates.
  • You can check the processed milk fat globules using a compound microscope. Pour back any discharged milk not properly homogenized into the machine until you achieve the best results.
  • Subsequently, you could use a double-stage homogenization for best results.

After Operation

After processing the milk:

  • Adjust the 3-way valve or multiport to turn the processed milk into the hopper.
  • After that, flush the inlet chamber and hopper with adequate water.
  • Then, release the first valve pressure. If it’s a double-stage operation, release the first and second valve pressure in that order.
  • You can perform other cleaning operations before switching off the machine entirely.

Some Homogenization Tips to Keep in Mind

For a long-lasting homogenizer and great operations, ensure you:

  • Always warm up the machine before regular operations commence
  • Regularly clean the inlet and discharge chambers or hoppers
  • Do not starve the machine of supplies when in operation.
  • Regularly assess the oil pressure
  • Never close or shut the 3-way valve when the homogenizer is active
  • Always inspect the homogenizer for leakages, wear, or breakages.
  • Constantly check for loose nuts or screws and tighten them.
  • Always observe the pressure gauges and ensure they have minimal or no errors. Even if there are errors, ensure you consider these errors when operating the machine.
  • Always dismantle valves carefully and keep them in place with less friction and humidity.
  • Regularly inspect the machine’s lubrication and oil levels.
  • Should the machine break down, take it to an expert for servicing.

 

Sensitivity to Oxidation

Vulnerability to oxidation is one of the side effects of homogenized milk. While enzyme action can be good, homogenization makes milk vulnerable to rancidity—a partial oxidation of the milk fat. 

Bacterial Action

Homogenization can increase the bacterial count in milk due to the passage from one medium to another. 

Effect on Health

While we may give much credit to the digestibility of homogenized milk, much thought isn’t given to the bad effects of homogenized milk. Lots of new studies suggest it may foster the growth of cancerous cells in the body.

Factors Affecting Homogenization of Milk

One or more of the following factors play a huge role in the homogenization of milk:

Pressure

Of all the factors that affect homogenization, pressure tops the list. Pressure is the foundation and working principle of milk homogenizers. It extends to the machine and material pressure, especially as the materials assume the shape of the chambers or hopper. 

Pressure determines the velocity at which the materials travel in the vessel and the vibrations of the fat globules while in the machine. In fact, without pressure, the materials will leave the chambers the same way, even if they pass through a small nozzle. 

Size of Raw Material

Another factor that may affect homogenization would be the raw material size. While this has no direct effect on the machine or output quality, it still affects parameters like the time and budget of the production process. 

Homogenization doesn’t end with using the homogenizer machine. You must consider the cost of operation, the labor force, and the output you need. All these depend on the raw material size. The bigger the projected output, the bigger the machine or laborers. Likewise, the bigger the production budget.

The Size of Fat Globules

Another notable factor that affects homogenization is the surface area to volume ratio and size of fat globules in homogenized milk. The bigger the fat globule size, the more homogenization will be needed to break it down. This explains why we sometimes need a double-stage homogenization to completely break down fat globules to the desired fine-grained size.

Diameter of Valve

The valve diameter also affects homogenization. Usually, the smaller the valve diameter, the higher the pressure and the slower the velocity when the piston pumps the fluids through the valve seat.

Industrial Processing of Milk

Now that we’ve learned about the homogenization of milk, we’ll see where it fits in the grand scheme of things or the entire milk processing hierarchy. In this section, we’ll talk about the industrial processing of milk with homogenization.

Milk Collection

The first step in milk processing is collecting the untreated or unprocessed milk from the store after harvesting it from the source, which could be a cow, goat, or corresponding milk-producing mammal. 

Centrifugal Separation

After collecting and sampling the milk, the next is to remove the impurities that would not be needed in the final production through centrifugation. Depending on the need, some milk products do not require a certain quantity of milk fat. Centrifugal separation is the best way to separate the milk from the cream and then resize the milk fat afterward. This process is called skimming of milk. 

Fortification

After skimming milk, adding extra nutrients or minerals to the solution becomes easier. Fortification is synthetically adding extra minerals and nutrients to the milk solution. This type of milk is called fortified milk and is usually recommended by nutritionists or dieticians, depending on the users’ deficiency.

Usually, vitamins A and D—for good eyesight and strong bones, respectively—are often added to fortified milk. Producers can also add supplements like folic acid and elements like zinc, iron, etc. Meanwhile, if these extra minerals are not needed, especially for fresh milk, you may skip this step and head over to the pasteurization process.

Pasteurization

Pasteurizing milk means heating the milk at certain temperatures for a specific time to kill potentially harmful and spoil-causing bacteria. Though we pasteurize milk after harvesting it from the farm, we still pasteurize it again after centrifugation and fortification.

The first pasteurization prevents the milk from spoiling before normal processing. The second is to kill harmful bacteria. That said, there are two major types of pasteurization: the Vat pasteurization and the high-temperature-short-time pasteurization (HTST).

The former involves subjecting the milk to heat till it gets to about 65ºC. In the case of the former, the temperature may rise to as high as 83ºC. Importantly, pasteurization is done under close and careful monitoring and conditions. If not, a little mistake could destroy the milk’s chemistry. 

Homogenization

After pasteurization, you can homogenize the milk by putting it in a homogenizer machine. We’ve already talked extensively on this. You can rewind the previous section for more information about homogenization.

Ultrafiltration

Like centrifugation, ultrafiltration is a separation technique used to minimize the cream portion of homogenized milk. The result is an ultrafiltered milk. This type of milk is used for special occasions or use cases. To do this, we pass the milk through a membranous material, filtering the liquid and some salts and minerals from other solid materials in the milk. This process is also known as osmosis or permeation.

Spray Drying

This involves removing the water from the milk concentrate at low temperatures that do not interfere with the milk’s chemistry. Usually, other processes are considered before this process takes place.

Packaging

Packaging is usually the final step before storage and distribution. This is where the powered, cream, whole, fresh, homogenized, or non-homogenized milk is eventually put in opaque containers, Tetra Paks, glasses, plastic bottles, laminates, cartons, cans, etc.

Types of Milk Processing

Because of the diversity in the milk industry, we approach milk processing with different techniques.

Cow Milk Processing

Dairy milk is the milk primarily obtained from cow breeds. Processing techniques for this milk include pasteurization, homogenization, separation, spray drying, etc. 

Coconut Milk Processing

There are a couple of ways to carry out the homogenization of coconut milk. Commercially, coconut milk is made by grinding and mixing with water, separating, then pasteurizing. 

Almond Milk Processing

The homogenization of almond milk is done by washing, soaking, grounding, and separating the almond seed from the chaff. Afterward, the liquid is fortified with additives and supplements, then pasteurized and packaged.

Condensed Milk Processing

This type of milk is obtained from cow milk. The only difference is that more amount of water is removed in condensed milk and then sugar is added to sweeten the milk.

Equipment Used in Milk Processing (A Complete Milk Equipment List)

We need machinery for efficient and streamlined milk processing. Some common types include milk pasteurizers, spray drying, centrifugation, and bottling machines, among others. Let’s see more about them below:

Milk Pasteurizer 

This machine is used to pasteurize or heat milk accurately. Pasteurizers are equipped with heating and timing tools to help maintain accuracy in the machine, especially during HTST pasteurization.

Spray Dryer Machine

Spray Dryers are used to produce milk powders. This machine follows the principle of evaporation and vaporization to eliminate water from homogenized milk. The final product is pushed to the packaging and distribution department.

Centrifugation Machine for Milk

This machine separates the liquid component of milk from the solid butterfat so that fat can be filtered or reduced considerably. This machine produces reduced fat and skimmed milk. 

Packaging Machine

The packaging machine is used in the packaging department to seal milk or dairy products in containers, Tetra Paks, cartons, or any opaque materials used to store milk. 

Milk Homogenizers

Homogenizers have been discussed extensively in this guide. They are used to break down and emulsify the fat globules in the water component of the milk.

Milk Mixing Tank

This machine aids in mixing additives, minerals, or supplements into milk after homogenization or filtration. One of the perks of using a milk mixing tank is its equal heat distribution, keeping the homogenization temperature of milk constant throughout the mixing process.

Milk Cooling Tank

This machine stores and cools milk quickly after pasteurization and homogenization. They maintain the milk’s freshness and quality during cooling. 

Frequently Asked Questions (FAQs)

1. What Is the Allowable Fat Content of Homogenized Milk?

Fat (or butterfat) is one of the notable components in milk. Normally, freshly harvested cow milk has about 3.6% to 4% butterfat. However, different milk products may have different specific fat composition.

The maximum allowable fat content of homogenized milk is 3.25%, which is common for whole milk. Other types of homogenized milk, like low-fat, skimmed, reduced-fat, etc., have butterfat below 3%.

2. What Is the Role of Caseins in Homogenized Milk?

Virtually all milk contains casein. It is a notable protein that plays a significant role in homogenized milk. This notability is no accident, as casein is responsible for emulsifying milk. I.e., it makes it easy to mix milk’s fat, solid, and liquid components to form a colloidal solution. 

Also, casein gives milk its characteristic white color. That is why cow milk is whiter than most milk because it contains 80% casein compared to 60% in human milk.

3. Difference Between Homogenized Milk and Whole Milk

Homogenized milk is any milk with blended components. This can be whole, skimmed, or low-fat milk. On the other hand, whole milk is just a homogenized milk with 3.25% milk fat. In comparison, low-fat milk has only 1% fat, while skimmed milk has none to 0.5% fat.

Conclusion

Homogenized milk is a type of milk whose fat has been broken down considerably and emulsified to form a colloidal milk solution. We can homogenize any plant or animal-based milk with immiscible elements. Although homogenization makes milk more appealing and usable for other dairy production, there are still dangers of homogenized milk, such as causing cancer or making milk vulnerable to harmful oxidation. 

To homogenize milk effectively, you need a functioning homogenizer machine. Also, you must properly warm up and inspect the machine before commencing full operation. For machines to have a longer life, ensure they are properly warmed up and inspected before commencing full operation. More so, ensure you buy machines from reputable sources like SaintyTec. You can check our array of production machines for tablets, gummies, granulation, blending and mixing, and all forms of liquid production like milk. 

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