Does Mozzarella Cheese Have Oil In It? Separating Fact from Pizza Grease

November 13, 2025 •

4 min read

According to the British Heart Foundation, a ball of mozzarella typically contains about 18% fat, which can cause confusion when a melted cheese dish appears visibly oily. This brings up the question, does Mozzarella cheese have oil in it, or is that greasy layer something else entirely?

Quick Summary

The 'oil' that appears on melted mozzarella is primarily milkfat separating from the cheese's protein matrix when heated. Factors like cheese age, fat content, and cooking temperature influence this natural 'oiling-off' process.

Key Points

Oiling-Off Explained: The 'oil' on melted mozzarella is milkfat separating from the cheese's protein matrix when heated.
Fat Content Matters: Cheeses with higher milkfat content, like whole-milk mozzarella, typically release more grease than part-skim varieties.
Age is a Factor: As mozzarella ages, the protein matrix weakens, allowing fat to be released more readily during heating.
Cooking Temperature: Higher heat accelerates protein breakdown and fat separation, leading to more oiling-off.
Added Oils vs. Milkfat: While natural mozzarella contains only milkfat, some commercial cheese analogues use added vegetable oils.
How to Reduce Greasiness: Use part-skim mozzarella, melt at a lower temperature, or blot excess oil with a paper towel.

The Science Behind Oiling-Off

What many people mistake for added oil is a natural phenomenon known as 'oiling-off'. Mozzarella, like other cheeses, is an emulsion of fat and proteins, with millions of tiny milkfat globules suspended within a protein (casein) matrix. When the cheese is heated, this delicate protein structure begins to weaken and shrink, especially when exposed to high temperatures or cooked for too long. As the matrix breaks down, it loses its ability to trap the fat globules, which then coalesce and rise to the surface as a visible, oily layer. This is the 'grease' you see on top of a hot slice of pizza.

Factors That Influence Oiling-Off

Several factors play a role in how much and how quickly a mozzarella will 'oil off':

Fat Content: Cheeses with a higher fat content, such as whole-milk mozzarella, will naturally release more fat when melted compared to lower-fat or part-skim versions. A reduction in fat content in mozzarella has been shown to significantly decrease free oil release.
Age and Proteolysis: The age of the cheese affects its protein structure. A regular cultured mozzarella needs a week to 10 days to break down enough for the protein matrix to weaken and release fat. Excessive breakdown, known as proteolysis, can lead to more oiling-off.
Homogenization: If the milk used to make the cheese is not homogenized, the free oil formation increases with the percentage of fat. Homogenization of cheese milk has been found to greatly reduce free oil.
Moisture Content: Low-moisture mozzarella, often used on pizzas, contains a higher fat percentage on a dry matter basis than fresh mozzarella, which can lead to more oiling-off.

How to Minimize Oiling-Off

If you prefer less grease on your melted cheese, there are several kitchen techniques you can use:

Use the Right Mozzarella: Choose a part-skim or low-moisture part-skim mozzarella over a whole-milk variety to reduce the overall fat content. Fresh mozzarella, while higher in moisture, tends to release less fat when melted compared to low-moisture varieties, although its moisture can make the final dish watery.
Avoid Overheating: Melt the cheese slowly and gently over lower heat. High heat accelerates the separation of fat and protein, leading to a greasy finish.
Blotting: For pizza, you can use a paper towel to blot the surface and absorb some of the excess grease after baking.
Add a Thickener: For cheese sauces, adding a thickener like flour or cornstarch can help absorb some of the excess fat and keep the emulsion stable, preventing an oily appearance.
Combine Cheeses: Mixing mozzarella with another cheese that is less prone to oiling-off can help balance the texture and fat release.

The Difference: Milkfat vs. Added Oils

For most natural mozzarella cheeses, the 'oil' is entirely milkfat. However, it is important to distinguish this from some processed cheese products or analogues, which may contain vegetable oils. Some commercial products are specifically manufactured with vegetable oils, such as palm oil, as a milkfat alternative for cost or functional reasons. Always check the ingredients list if you are concerned about vegetable oils in your cheese. One such product description confirms the inclusion of palm oil alongside milk solids. A scientific study also featured a mozzarella cheese analogue with palm-based oils as a milk fat alternative. Therefore, while authentic mozzarella does not have added oils, certain cheese-like products do.

Comparison of Mozzarella Varieties

The Impact of Age on Melting

As mozzarella ages, enzymes from starter cultures and rennet break down the protein matrix in a process called proteolysis. This breakdown, which takes about a week to 10 days for regular cultured mozzarella, is what allows the cheese to melt properly and release some of its trapped fat. Very fresh mozzarella, aged only one to three days, will not melt as evenly and typically won't release oil. If the cheese is allowed to age too long, excessive proteolysis can occur, leading to a weaker protein matrix and more aggressive oiling-off. This maturation period is a crucial balance for pizza mozzarella, where the peak performance for qualities like stretch and even oil release is typically between 21 and 35 days. For a deeper dive into the science, you can read more about how homogenization and proteolysis affect free oil formation on ScienceDirect.

Conclusion

In conclusion, the 'oil' that appears on melted mozzarella is not oil that has been added to the cheese but rather milkfat that has separated from the protein structure under heat. This natural process, called oiling-off, is influenced by the cheese's fat content, moisture level, age, and manufacturing process. While some commercial cheese analogues may contain added vegetable oils, natural mozzarella cheese is composed of milkfat. By understanding the science behind oiling-off, you can take steps to minimize it in your cooking, whether by choosing a lower-fat cheese, using a lower cooking temperature, or simply blotting the excess from your finished dish.

Frequently Asked Questions

The grease on your pizza comes mainly from the fat in the cheese (milkfat) and any meat toppings like pepperoni or sausage. When heated, this fat melts and rises to the surface, creating an oily layer.

You can minimize oiliness by using part-skim or low-moisture part-skim mozzarella, cooking at a lower temperature, and blotting the excess oil with a paper towel after baking.

The oil on mozzarella is milkfat, which contains saturated fat. While not inherently 'bad,' a diet high in saturated fat should be limited. Part-skim mozzarella has less total and saturated fat than whole-milk varieties.

Low-moisture mozzarella, commonly used on pizza, has a higher fat concentration on a dry basis and a weaker protein structure that leads to more noticeable oiling-off when melted. Fresh mozzarella retains more moisture and tends to release less free fat, though it can make the dish watery.

Many cheeses will release fat when heated due to the breakdown of their protein matrix. However, the extent of oiling-off varies widely depending on the cheese's fat content, moisture, and age.

Yes, some commercial cheese products and analogues are made with vegetable oils, such as palm oil, instead of milkfat. You can identify these by checking the ingredients list on the packaging.

Yes, low-fat mozzarella generally releases less free oil when heated because it contains less total fat to begin with. Some low-fat versions are even designed to release just enough fat to melt correctly and prevent excessive dehydration.