The first step to reusing frying oil is letting it cool completely and straining out the fried crumbs left behind. Leftover crumbs burn quickly during the next fry and lower the oil's smoke point.
Strained oil should be kept in a dark, sealed container somewhere cool and dark; stored this way, it can usually be reused three to four times.
Why Does the Oil Need Straining?
Flour, breadcrumbs or bits of batter that fall into the oil during frying darken with heat the longer they sit in it, leaving a bitter taste. These crumbs also make the oil smoke faster next time and shorten its usable life.
Straining removes those crumbs, preserving both the oil's flavor and how long it lasts; unstrained oil usually becomes unusable after just one or two fries.
Let the Oil Cool
After frying, take the oil off the heat and let it come down to room temperature, usually about an hour. Trying to strain hot oil is dangerous and can also break the crumbs into finer bits that slip through the strainer.
Strain Through Cheesecloth or a Coffee Filter
Pour the cooled oil through cheesecloth or a coffee filter set inside a funnel into a clean container. This catches even the tiny, hard-to-see crumbs and leaves the oil noticeably clearer.
Store It in a Dark, Sealed Container
Transfer the strained oil into a dark, opaque bottle or sealed container and keep it in a cool, dark cupboard. Since light and heat speed up oil breaking down, storing it in the fridge is also an option.
How Many Times Can You Reuse It?
Oil that's been strained and stored properly can usually go through three to four more fries; it darkens a bit more each time, which is normal. Signs that oil is done for good include heavy foaming, a sharp, bitter smell and noticeable darkening.
Oil used to fry something strong-smelling like fish shouldn't be reused for other foods, since the smell carries over and spoils the next dish's flavor. A noticeable drop in the oil's volume is often another sign it's been used many times and is due for a change.
What Container Should You Strain the Oil Into?
Pouring the strained oil back into its original bottle, or into a clean, wide-mouthed glass jar, is a practical solution; glass is usually preferred over plastic, since plastic can hold onto the oil's smell over time.
A tight-sealing lid also cuts down on air exposure and keeps other kitchen smells from seeping into the oil.
What Should You Watch For While Straining?
Making sure the oil is fully cool before straining matters both for safety and because the strainer catches fine crumbs more effectively that way; warm oil flows through faster but can leave small particles behind.
Cheesecloth should be treated as single-use, and a fresh coffee filter used each time as well; reusing a dirty filter can mix old crumbs back into the oil.
In Short
The formula for getting more use out of frying oil comes down to cooling, straining and storing it in a dark container. Following these three steps lets the oil be reused safely a few more times, though not indefinitely.