Does Heating Milk Reduce Protein?

November 14, 2025 •

6 min read

While the total protein content of milk remains constant after heating, a study examining heat treatments found that specific heat-sensitive whey proteins can be substantially diminished in their native form. Understanding this process requires differentiating between protein quantity and structural changes, which affect how your body uses the nutrients.

Quick Summary

Heating milk denatures its proteins, particularly the whey component, but does not destroy the total protein content. The extent of this structural change depends on the temperature and duration of heating. This process can slightly alter protein digestibility and bioavailability, with minimal impact from pasteurization and more notable effects from high-heat treatments like boiling or UHT processing.

Key Points

Protein Isn't Destroyed: Heating milk denatures proteins, particularly whey, but it does not remove or destroy the amino acids that form the protein.
Whey and Casein React Differently: Casein, the major protein in milk, is very heat-stable, while whey protein is sensitive to heat and denatures readily.
Pasteurization vs. Boiling: Lower heat pasteurization (HTST) has a minimal impact on protein structure and digestibility compared to boiling or UHT treatments, which cause more extensive denaturation.
Slightly Reduced Digestibility: Excessive heating can cause protein aggregation, which may slightly decrease the efficiency of protein digestion and absorption, but the effect is generally minor.
Potential for Allergic Relief: Denaturation from heat can alter the allergenic properties of milk proteins, potentially making cooked milk products more tolerable for some individuals with milk allergies.
Nutritional Value Largely Maintained: Despite structural changes, heated milk remains a high-quality source of protein, with any loss of availability being insignificant for a healthy diet.

The Science of Milk Protein Denaturation

Milk's protein content consists of two main types: casein (approximately 80%) and whey (approximately 20%). These two protein families behave very differently when subjected to heat, which is key to understanding how temperature affects milk's nutritional profile.

Casein exists in milk as large, stable colloidal particles called micelles. Its structure is very heat-resistant, meaning it is largely unaffected by normal heating and even boiling. Whey protein, on the other hand, is composed of smaller, globular proteins that are highly heat-sensitive. The two major whey proteins, beta-lactoglobulin ($\beta$-Lg) and alpha-lactalbumin ($\alpha$-La), begin to unfold, or 'denature,' at temperatures above 65°C.

Denaturation is a process where a protein loses its three-dimensional structure due to external factors like heat. This unfolding exposes reactive groups within the protein, such as sulfhydryl groups in beta-lactoglobulin. These exposed groups can then react with each other or with the casein micelles, causing the proteins to aggregate and form larger complexes. These aggregates change the physical properties of the milk, affecting taste, texture, and potentially digestibility.

Pasteurization vs. Boiling: A Comparison of Effects

The impact of heating on milk protein is highly dependent on the temperature and time. This is evident when comparing common thermal treatments like pasteurization and boiling. The goal of all heat treatments is to ensure safety by killing harmful bacteria, but the side effects on protein vary significantly.

Pasteurization

Low-Temperature Long-Time (LTLT) Pasteurization: Typically involves heating milk to around 63°C for 30 minutes. This causes minimal denaturation of whey proteins and does not significantly affect the overall protein quality or digestibility.
High-Temperature Short-Time (HTST) Pasteurization: This common method heats milk to at least 72°C for 15 seconds. While effective at killing pathogens, it does cause some denaturation of whey proteins, with a notable reduction in bioactive proteins like immunoglobulins. However, the impact on total protein nutrition is considered minor.

Boiling and UHT Treatment

Boiling: Heating milk to its boiling point (around 95°C) and above causes substantial denaturation and aggregation of whey proteins. Prolonged boiling can also lead to the Maillard reaction, a chemical interaction between proteins and sugars that affects flavor and can potentially decrease the availability of some amino acids, like lysine.
Ultra-High Temperature (UHT) Treatment: This process heats milk to very high temperatures (135–150°C) for a few seconds. It is designed to sterilize milk for long-term storage without refrigeration. It causes extensive whey protein denaturation, which can lead to a slight decrease in overall protein digestibility compared to regular pasteurized milk.

Comparison of Milk Heating Methods


Feature	Raw Milk	Pasteurized Milk (HTST)	Boiled Milk	UHT Milk
Whey Protein Denaturation	Minimal	Partial, but relatively minor impact on nutritional value.	Substantial, with significant structural changes.	Extensive and irreversible.
Casein Protein Integrity	Intact	Largely stable.	Remains stable even at high temperatures.	Remains stable.
Overall Protein Value	High	High, with very little nutritional impact from heating.	Very good, but may experience minor reductions in digestibility.	Very good, with a slight reduction in protein retention reported in some studies.
Effect on Digestibility	High digestibility	Slightly altered but remains highly digestible.	Altered structure can lead to slightly reduced digestibility for some.	Some studies show reduced protein retention in the body.
Safety	High risk of pathogens.	Safe for consumption.	Safe after proper boiling, kills pathogens.	Very safe, sterile for extended shelf life.

The Protein Myth and Digestibility

So, does heating milk truly reduce the protein? The answer is nuanced. The total quantity of protein remains the same; the amino acids are still present. However, excessive heat can alter the protein's structure, which can slightly decrease its digestibility and bioavailability, or how easily the body can absorb and utilize it.

For example, studies have shown that ultra-heat-treated (UHT) milk can result in a slightly lower rate of protein retention by the body compared to regular pasteurized milk. This is because the heat-induced aggregation of proteins can sometimes make them less accessible to digestive enzymes. However, this is not a significant concern for most healthy adults consuming a balanced diet. The health benefits of drinking safe, pasteurized milk far outweigh any minimal changes to protein digestibility.

There is one area where protein denaturation is viewed as beneficial: for individuals with a milk protein allergy. When proteins like whey denature, their shape changes, and the epitopes (the parts of the molecule that the immune system recognizes) may be altered. Some research shows that children with milk allergies can tolerate cooked or baked milk more easily than raw milk.

A Balanced Perspective on Heated Milk

Ultimately, the choice of whether to heat milk and to what extent depends on your priorities: safety, taste, and nutritional profile. For a balanced diet, the minor differences in protein digestibility between pasteurized and boiled milk are largely negligible. The most important takeaway is that milk remains a high-quality source of protein, regardless of standard heat treatment.

Prioritize Safety: Always opt for pasteurized milk unless you are certain of the raw milk's source. If using raw milk, boil it to kill harmful pathogens.
Understand Your Needs: If you or your children have a milk protein allergy, heat treatment may offer a way to consume milk products with fewer allergic reactions, but consult a doctor first.
Keep it Moderate: For minimal impact on heat-sensitive components like vitamins, choose pasteurized over boiled or UHT milk when possible.

This nuanced understanding of heat's effect on milk protein helps to dispel the myth that all heating destroys milk's protein content. Instead, it offers a more complete picture of the chemical changes at play and their actual health implications. For more information on dietary choices, visit a reliable source like the U.S. Department of Agriculture's Nutrition.gov website to ensure your eating habits align with current nutritional science.

What Really Happens to Milk Protein When Heated?

Here’s a look at the specific processes that unfold when milk is heated, a process more complex than simple protein 'destruction.'

1. Denaturation of Whey Proteins: As milk is heated above 65°C, the globular whey proteins, such as beta-lactoglobulin, begin to lose their compact, folded structure and unwind. This process is more pronounced and irreversible at higher temperatures, like those used in boiling or UHT processing.

2. Interaction with Casein Micelles: Once denatured, the whey proteins can interact with the more stable casein micelles, attaching to their surfaces. This interaction affects the milk's physical properties, like viscosity and heat stability, and is a key step in cheese making.

3. Formation of Aggregates: The unfolded whey proteins don't just attach to casein; they also aggregate with other denatured whey proteins, forming larger polymers. This is often driven by thiol-disulfide bond exchange reactions involving beta-lactoglobulin.

4. Maillard Reaction: With prolonged, high-temperature heating, a chemical reaction known as the Maillard reaction occurs between milk's lactose (sugar) and its proteins. This process is responsible for the slightly brownish color and altered flavor of boiled milk and can make the amino acid lysine less available for absorption.

5. Effect on Digestibility: While the heat does not remove protein from the milk, these structural changes and aggregations can alter how efficiently our body's digestive enzymes can break them down. For example, the formation of large aggregates can slow down digestion, leading to a slightly different absorption profile. However, the effect on overall nutritional value in a balanced diet is minimal.

Conclusion: Heating Alters, Not Eliminates, Milk Protein

The notion that heating milk eliminates its protein is a common misconception. The scientific consensus is that heat causes milk proteins, particularly whey proteins, to denature—they change their physical shape—but they do not disappear from the milk. Standard pasteurization has a minimal effect on the overall nutritional value and protein availability, preserving the milk's goodness while ensuring safety. High-temperature treatments like boiling and UHT cause more extensive denaturation and aggregation, which can lead to minor changes in protein digestibility and other sensory properties. For most people, these changes are not nutritionally significant. For those with milk protein allergies, however, these heat-induced alterations can sometimes make milk more tolerable. Ultimately, heating milk is a necessary step for safety, and the milk remains an excellent source of high-quality protein.

Frequently Asked Questions

Boiling milk causes protein denaturation, where whey proteins change their shape. While this can slightly alter how easily the protein is digested, the total amount of protein remains the same, and the milk's overall nutritional value is largely retained.

No, heating does not destroy the protein in milk. Instead, it causes the proteins to denature or unfold. The amino acid building blocks are still present, but their structure has been altered by the heat.

Research indicates that the heat from pasteurization has a minimal impact on milk protein. Studies have found no significant difference in the protein efficiency or digestibility between pasteurized and raw milk in humans.

Denaturation is the process of a protein unfolding and losing its native structure due to heat. In milk, this primarily affects whey proteins, causing them to aggregate. This change can alter texture and potentially make digestion slightly less efficient, but it does not eliminate the protein's nutritional value.

Yes, excessive or prolonged heating can cause losses of heat-sensitive vitamins, particularly B vitamins like riboflavin and folate. It can also trigger the Maillard reaction, which can affect the availability of the amino acid lysine.

While UHT treatment causes more extensive denaturation of whey protein than pasteurization, the milk remains a highly nutritious food. Some studies suggest a slight decrease in protein digestibility with UHT milk compared to pasteurized, but the difference is small.

For some individuals with a milk protein allergy, heat-induced denaturation of whey proteins can alter the immune-triggering components. This can make cooked or baked milk products more tolerable, though this varies by individual.

Casein is relatively heat-stable, retaining its structure even when milk is boiled. Whey protein, however, is very heat-sensitive and denatures at high temperatures. This denaturation and subsequent aggregation is what accounts for most heat-induced changes in milk protein.