Menu
Search
Menu
Close

We make mistakes so you don’t have to.

Get unlimited access to ALL our foolproof recipes, unbiased equipment reviews and ingredient ratings. Guaranteed to work for you.

Try CooksIllustrated.com Free for 14 Days

Email is required
How we use your email address

Used Fryer Oil

By Cook's Illustrated Published May 2009

In deep-frying, the first batch is never the best. Food writer Russ Parsons explains in How to Read a French Fry that fry oil has five stages: break-in (too fresh to fry well), fresh, optimum, degrading (on the way to spoiling), and runaway (dark, smelly, and prone to smoking). Food fried in optimum oil is golden and crisp. Break-in and fresh oil yield paler, less crisp food. Degrading and runaway oil produce dark, greasy food with rancid odors. Could we create optimum oil by mixing used and new?

Experiment

We fried shrimp, fish, and French fries in fresh oil and in a mixture of fresh oil and oil that had been used once to make French fries (and then strained through a coffee filter to remove any solids).

Results

Food fried in the mix of new and used oil was crisper and more uniformly golden than food fried in fresh oil.

Explanation

Oil that is too fresh can’t penetrate the barrier of moisture that surrounds food as it fries. Over time, as the oil continues to be exposed to heat, it breaks down, producing slippery, soaplike compounds that can penetrate the water barrier. This increased contact between oil and food promotes browning and crispness.

Bottom Line

Save a cup or two of used oil to mix with fresh the next time you fry (we found that a ratio of 1 cup of used oil to 5 cups of fresh oil worked best). Just make sure that you don’t save oil used to fry fish—the smell will permeate the new oil.