Guest Columns

Perspective:
Cheese Technology

Techniques available to reduce oiling-off defect of Mozzarella

Dr. Mali Reddy

Dr. Mali Reddy serves as president of the American Dairy and Food Consulting Laboratories and International Media and Cultures (IMAC Inc.), Denver, Colo. He holds several degrees including M.S. and Ph.D. degrees from Iowa State University in food technology and microbiology. He is a guest columnist for this week’s issue of Cheese Market News®.

In May, I wrote a guest column on the browning and burning defect of Mozzarella on pizza. Today we will examine another serious Mozzarella defect — oiling-off or excess oil production from Mozzarella on pizza.

What is oiling-off? Why do some Mozzarella cheeses produce more oil than others? There are four types of Mozzarella cheeses which qualify as standard of identity products, according to the Code of Federal Regulations (CRF) of the United States of America. They are:

• Mozzarella Cheese: Minimum milkfat 45 percent by weight of the solids, and the moisture content is more than 52 percent but not more than 60 percent.

• Low-moisture Mozzarella Cheese: The minimum milkfat content is 45 percent by weight of the solids, and the moisture content is more than 45 percent but not more than 52 percent by weight.

• Part-skim Mozzarella Cheese: The minimum milkfat content is 30 percent and not more than 45 percent by weight of the solids, and the moisture content is more than 52 percent but not more than 60 percent.

• Low-moisture Part-skim Mozzarella Cheese: The minimum milk fat content is 30 percent but not more than 45 percent on the solids basis , and the moisture content is more than 45 percent but not more than 52 percent by weight.

According to the CFR, the highest amount of fat is present in low-moisture Mozzarella cheeses. If such a cheese is baked on pizza, anyone can expect more oil coming out on the cheese surface. However in reality if it does oil-off, it is considered a defect.

Cheese’s fat is physically trapped in the cheese protein matrix. When Mozzarella cheese is fresh — one to three days old — it will not melt on pizza and does not release oil. Of course the exception is brine-to-dice cheese, made using direct acidification and other manipulations. Regular cultured Mozzarella cheese made without using acids will start to melt and release fat after protein breaks down with the aid of starter culture and calf rennet or other microbial coagulating enzymes. It will take a week to 10 days for this transformation. If the protein breakdown is excessive in the Mozzarella due to a highly proteolytic starter, the type of coagulant used, the integral nature of the protein and fat in the raw milk and/or the level of psychrotrophic bacteria in the raw milk, such a cheese will liberate more fat on the pizza because the protein matrix is not strong enough to hold and release the fat in a timely manner as the pizza bakes. If excess oil is liberated early, such oil will fry the cheese and induce a bubble gum effect rather than having uniform melt with the fewest oil puddles.

Another factor which contributes to the oiling-off defect is the use of casein and/or high protein base secondary starters. Since the secondary starter proteins are high heat treated during the manufacture of the starter, such a highly denatured protein in the cheese matrix will break down faster and thus contribute to this defect. On the other hand, whey protein base secondary starter will hold more moisture and thus accelerate the break down of cheese, causing the oiling-off defect on pizza. Thus, care must be taken to properly select the primary and secondary starters to minimize this serious defect. Secondary starter usage is an excellent way to improve the quality of cheese, and it is being practiced in the dairy industry.

Just because the low-moisture Mozzarella cheese has more fat does not mean it should oil-off more than the part-skim or low-moisture part-skim Mozzarella cheese. Even though the low-moisture part-skim Mozzarella cheese has the lowest amount of fat and the lowest amount of moisture, it should release a sufficient amount of fat to give a uniform melt. If the protein integrity is not maintained, even a low-moisture part-skim Mozzarella will exhibit the oiling-off defect. It is a myth in the industry that such Mozzarella cheese will not oil-off on pizza. Consequently, cheese manufacturers tend to produce cheese at lowest permissible moisture levels, rather than staying at the high end approved by the standard of identity of that particular cheese. Since every percentage of moisture contributes to the bottom line, rather than making cheese at the low end of moisture, everybody should try to push it toward the high end.

This is where technology comes in. By preserving the raw milk, protein integrity can be improved. We ran experiments and proved that milk sitting in the silo longer than 24 hours or equal to 24 hours tends to lose protein by 0.08 percent due to proteolysis by the thermostable enzymes of the psychrotrophs. Such milk also will lose fat by 0.06 percent due to lipolytic enzymes.

Surprisingly, such a miniscule amount of protein loss not only makes cheese exhibit defects such as oiling-off, abnormal flavor, etc., it creates serious economic loss to the cheese plant as well.

A plant processing 1 million pounds of milk a day, working six to seven days a week, will end up losing around $1 million net profit at the end of the year because of the loss of protein (0.08 percent) and fat (0.06 percent). Total quality management (TQM) of raw milk is extremely important to maintain the maximum returns through better cheese yields and also to eliminate defects such as oiling-off, off-flavors and soft body.

To summarize, the following precautions must be undertaken to eliminate this oiling-off defect:

1. Protect and preserve the raw milk during storage in the milk silo. Do not let psychrotrophs rob profit and cause cheese defects. There are excellent systems available to protect the raw milk in silos. Do not ignore research, and learn to take advantage of such newer systems.

2. Select the starter cultures, media, and method of neutralization techniques to minimize the milk protein loss due to proteolysis in cheesemaking. Do not get carried away with too fast-acting starter cultures. Such cultures will have a tendency to break more milk proteins, especially casein.

3. Select the secondary starter and be very cautious about excessive casein base and/or whey protein base secondary starter media and their heat treatments. Secondary starter is an excellent idea to improve the quality of cheese, and they work well. However, select the proper media composition and cultures to eliminate soft body and thus oiling-off defects. There are some excellent media available on the market, so shop around and get the best.

4. Select a proper coagulating enzyme to minimize the proteolysis. It is a well-known fact that microbial coagulants will proteolyze more than the calf rennet.

5. If you are using coccus and rod bulk cultures, maintain their ratio to obtain an excellent quality cheese. These two organisms are used for a specific purpose; balance them to get the best cheese with no defects.

6. Finally, stick to good manufacturing practices and proven modern cheese technologies to make cheese without defects and with good cheese yields to keep you happy in the competitive business world.

CMN

The views expressed by CMN’s guest columnists are their own opinions and do not necessarily reflect those of Cheese Market News®.

© 2025 Cheese Market News • Quarne Publishing, LLC • Legal Information • Online Privacy Policy • Terms and Conditions
Cheese Market News • Business/Advertising Office: P.O. Box 628254 • Middleton, WI 53562 • 608/831-6002
Cheese Market News • Editorial Office: 5315 Wall Street, Suite 100 • Madison, WI 53718 • 608/288-9090