If the fryer oil foams when deep frying, is it still good to use?

– Herb Pickell, private club, Bridgeport, Mich.


Foaming is common in frying. Although oil is liquid, it is a dry-heat cooking method, as there is no moisture in oil. When food is dropped into the hot oil, the moisture in the food rises to the surface to evaporate. This causes the characteristic bubbling of the oil, and when the associated moisture, starch, and impurities are left behind, they may create a foam on the surface.

When we talk about “good to use,” we are really talking about two things—safety and quality. In terms of food safety, foam does not indicate a problem with the oil per se. However, it is a sign that the oil has been well-used over time. With age and repeated use, the oil may develop rancid flavors and its structure will break down, leaving it less effective. The foam is a sign that the oil needs to be filtered and may need to be recycled completely and exchanged with new oil. You can use a commercially available test kit to monitor the breakdown of the oil.

There are some simple things you can do to prevent the foaming and also extend the life of your oil:

  • Use an oil specifically designed for deep frying.
  • Make sure battered and breaded items are free from excess coating.
  • Blanch high-moisture and long-cooking items such as french fries at a lower temperature first and crisp in a hotter fryer to finish.
  • Avoid heating the oil to excess (ideally below 375 degrees Fahrenheit).
  • Skim out any particles left behind between baskets.
  • Filter often.

More on extending the life of frying oil here.

Source: Originally published on by  Jonathan Deutsch, Ph.D. on Feb. 28, 2018

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