Why do fryers bubble over?

Why Is My Oil Foaming? Commercial Deep Frying Explained

Deep frying works when heated oil or shortening removes food's moisture. As vegetables, fries, or breaded proteins are lowered into hot oil—usually heated between 350 and 375 degrees Fahrenheit—the water on the surface of the food reaches its boiling point. Bubbles forming on the oil's surface are normal, but if not controlled, they can foam up and overflow, risking employee safety and creating a fire hazard.

Why Does Oil Foam When Frying?

One of the most common reasons oil foams up is because of degraded oil. Break down occurs over time when the same oil is used for repeated frying. This practice saves money, but without proper oil care, it ruins your product. Factors like heat, contamination, and light cause oil to break down. This degradation process, called oxidation, yields unusable oil that affects flavor and bubbles up more than usual.1

Excessive bubbling may also occur when there's too much water in your fryer basket. Overloading product increases moisture, which causes more surface bubbling. Experiment with product levels to maintain both efficiency and safety.

Improper cleaning in fryers also causes foaming. If water remains in the pot, it will cause bubbling when the oil heats up. Residual cleaner solution or crumb buildup can also degrade oil.

What to Do When Oil Is Foaming

If your oil is bubbling up too much, turn off the heat before it overflows. Remove your product and let the oil cool completely. Next, you'll need to troubleshoot your frying process to identify the cause of foaming.

How to Stop Oil from Foaming

  • Change cooking oil or shortening when it starts to degrade; look for excessive foaming, rancid smell, or dark color2
  • Filter oil after each use and store it in an airtight container away from direct sunlight
  • Thoroughly clean, rinse, and dry the fryer pot before use, removing leftover crumbs and cleaning residue
  • Pat washed or wet ingredients dry before frying them to reduce surface moisture
  • Don't overcrowd your fryer basket
  • Don't heat oil beyond its smoke point

Additional Safety Tips

Deep frying is a dangerous cooking method. Risks include oil burns, vats bubbling over, and grease fires. To ensure your safety, follow these guidelines:

  • Never use water to put out a grease fire. Keep a grease-rated fire extinguisher near the frying station
  • Slowly lower food into the fryer with your basket to avoid splashes and burns
  • Use gloves and an apron when handling hot oil
  • Cook foods like poultry and fish to safe internal temperatures. Remove items from oil when checking their temperature

References

  1. Individual and combined effects of frying load and deteriorated polar compounds on the foaming of edible oil Science Direct. Accessed July 2025
  2. How Many Times Can I Re-Use Fry Oil | Ask the Food Lab Serious Eats. Accessed July 2025
  3. Deep Fat Frying and Food Safety. USDA. Accessed July 2025