How to Use Leftover Cooking Oil and Fats

by Sherri Brooks Vinton


When you grow up around Southerners you know the value of a good slick of drippings in the pan. In my grandmother Lucille’s kitchen, there wasn’t a drop of bacon grease that was wasted. She sautéed vegetables in it, cooked her cornbread in it, smeared it on biscuits instead of butter. During tough times, my grandfather would work a full week only to be paid with a slab of fatback — a cut of pork that is, like it sounds, a piece of fat. That fatback and what was in the field was what they had to eat until better work came around.

Saving up fat and using it well isn’t just good practice for the frugal cook. Fat is fuel. Fat is flavor. And it’s better to taste it than waste it.

Using Up Oils and Fats

Animal and plant based, there are oils and fats for every cooking application, diet regimen and religious belief. Many oils and fats, such as canola oil, have become so common on our pantry shelves that we have lost track of how resource intensive they can be to produce. Others, such as artisanal olive oils, are so highly valued we cooks find ourselves rationing them out for only very special occasions. With a little time in the kitchen, animal fats such as lard, can be made at home often from meat trimmings or by retrieving fat created by cooking meat. Some basic guidelines will help you get the most out of them.

Storing Cooking Oils

Heat, light and air spoil oil and fat. As a rule, the more flavorful and fragrant the oil or fat, the more fragile. Fine olive oils and nut oils, for example, have amazing taste. They need to be kept properly and treated gently to preserve it. The more refined the oil, the more neutral its taste and the more stable it will be in storage and in cooking.

So, while you can store your processed, neutral oils at room temperature, flavorful nut oils and rendered animal fats should be refrigerated to keep them tip top. Avoid keeping them over or next to the stove. While this might be a convenient location, subjecting even the most rugged oil to warm temperatures will shorten its shelf life significantly.

And it’s always a good idea to keep even room temperature oils out of the light by either decanting them into a dark or opaque container or storing them in a cabinet when not in use.

You want to rotate your stock regularly. Buy oil in bottles that are only as big as you need; a quantity that you will go through in a few weeks. It’s no savings to buy a gallon of vegetable oil if you are going to pitch most of it out because it went off before you couldn’t get through it. If you’ve ever been rummaging through your cabinets and come across a bottle of oil that feels tacky on the outside, chances are the oil inside the bottle is old enough to have gone rancid. Give it a sniff. Neutral oils should have little or no scent at all. If it smells acrid or musty, so will your dish.

Cooking with Oils and Fats

The type of oil you use in a dish depends not only on the flavor you want on the plate but the cooking method you will use to get it there. The most delicate, richly flavored oils should not be heated at all. You can use them on cold dishes, such as salad dressings, or drizzle them on finished dishes to anoint them with the flavor of the oil but not subject it to any heat.

The higher the cooking temperature, generally, the more refined oil you want to use. Refining removes volatile compounds that create acrid or burnt tastes. Ghee, which is butter that has had its milk solids removed, is a great example of this. With the milk solids intact, butter turns brown and toasty when heated, imparting a warm, hazelnut flavor to dishes. Just beyond that point, however, the milk solids burn. Remove those solids, however, and you can heat the clarified butter at a much higher temperature, giving you that rich buttery flavor with less risk of burning.

The temperature at which oils and fats break down or (gasp!) catch fire is called the smoke point or flash point. While there are some exceptions, neutral oils, such as safflower, peanut, sunflower and canola oils have the highest flash points and are the best choices for high heat cooking. Chose them for deep frying, wok cooking or high heat searing.

Reusing Oils and Fats

Many oils and fats can be reused. This is particularly important to keep in mind when using copious amounts of oil for deep frying. Just cool and strain the oil carefully through a fine mesh sieve or a double layer of cheesecloth to remove any food particles. Cover and store for another round, being sure to mark on the container the date of each use and what was cooked in it.

Each time you reuse your oil, you will lower the flash point. Best to use repurposed oil for only a couple of rounds of high temperature recipes. But you don’t have to limit reused oil to high heat cooking. The oil that was used to fry potatoes can be strained and used tablespoon by tablespoon in any dish that uses oil such as baked goods, salad dressings, sautéed foods and more.

Oil that has been used to cook highly flavored foods, such as fish, may impart that taste to the next dish, so be sure to reuse your oil in recipes with compatible flavors. Fish and chips, then fried shrimp would be fine. Fish and chips then fried chicken may taste a bit off. It’s also important to keep track of the foods that have been cooked in the oil to avoid accidentally exposing an allergy sufferer to an ingredient that isn’t apparent on the plate. French fries, for example, that are cooked in the same oil as shrimp can trigger the same allergic reaction as consuming the shellfish itself.

As you reuse your oil or store it, check for signs of degradation such as color change or rancid or spoiled odors. Cloudy or foamy oil should also be discarded.


Want to go the extra mile? Spent oil doesn’t have to be the end of the road for this valuable resource. Some drivers, particularly those with extended commutes, have converted their diesel engines to run on used cooking oil. It’s a technology that is accessible to anyone who is willing to collect the oil, usually from neighborhood restaurants, and strain it before use.

If you find yourself with an abundance of oil, perhaps after a holiday turkey or fish fry, you can bring it to a local collection center where it will be disposed of properly.

Fat from Scratch

While plant-based oils have been touted for years as being the most healthful, more eaters are returning to animal fats as part of a balanced diet. There’s a lot to love about them. Sourced well, from area farms that support responsible animal husbandry, animal fats can be a local and sustainable. Animal fat from pastured animals is also rich in omega-3 fatty acids, Vitamin E and CLA — all components that support our health.

One of the best things about animal fats is that they are a byproduct of butchering. In the home kitchen animal fats would normally go to waste. By using them in your cooking, you are turning a product that would normally get discarded into a useful and flavorful food.

You can process them in your own kitchen. Unlike many highly refined oils that undergo a complex chemically-fueled chain of events, animal fats are the result of a very simple process, described below, that need use nothing more than gentle heat to make it kitchen ready.

Rendering Fats

There are a few ways to prepare animal fats for use. Cooking down fat to clarify it is called rendering. Animal fat is cut into thin strips or diced and heated slowly in a heavy-bottomed pot. The clarified fat cooks out and any skin or tissue becomes crispy and brown and is strained out (and eaten as a tasty treat).

Any fat of any animal can be used but in larger animals the creamy white fat that surrounds the kidneys, which is confusingly called “leaf lard” even before it is rendered, is prized for its quality and flavor. The clarified fat is called lard, if it is from a pig. Suet, the fat from a sheep, cow or steer, is called tallow when rendered. In Jewish cuisine, “schmaltz” is the rendered fat of a chicken, flavored by an onion added to the simmering fat. The skin or tissue that comes out of the process is prized for its luscious flavor and is often enjoyed as a treat for the cook or served to lucky diners. Crisp, brown cracklings result from rendering fat from pigs, cows or sheep and gribenes from making schmaltz.

Lard is famous for its performance in baked goods, where it creates a shatteringly crisp crust. Before partially hydrogenated shortenings became popular, lard was the “go to” fat for blue ribbon pies. British Yorkshire pudding and mince pies rely on tallow in their traditional recipes. Chopped liver and matzah ball soup make good use of schmaltz but Jewish diners are also known to enjoy it simply slathered on a piece of bread.

Wet Rendering

Another method for rendering fat is to simmer diced fat in water. The fat will melt and render out and any other material will fall to the bottom of the pot. On the plus side, you don’t need to strain fat rendered this way. But in the “con” column, you miss out on any crispy cracklings that would brown up in the pan. The best way to separate this fat from the water is to refrigerate the whole shebang. Let the pot of water and rendered fat cool to room temperature and then refrigerate overnight. The fat will solidify into a solid disk. Just run a sharp knife around the outer edge of the fat and you will be able to remove the disk in one piece. Dry it off and you can slice it into smaller pieces for easy storage.

You can use a similar process for retrieving the fat that rises from a pot of stock. Left overnight in the refrigerator, the fat will rise to the top and solidify. It can then be scooped off for later use. If the resulting fat is too wet or you pick up too much liquid in the defatting process, you can simply simmer it in a small saucepan until the liquid has evaporated, leaving behind usable fat.


The fat that is shed from cooking meat is referred to as the “drippings.” The lovely liquid in the bottom of your roaster and the fat from your seared steak are both examples of this flavorful and useful stuff. It is worth gathering up and putting to work. While all roasts will throw off fat as they cook, some provide a more ample supply than others. Ducks and geese are notoriously generous and will produce cups to quarts of useful fat. Strain it and refrigerate for a month or freeze for up to six months to use in your cooking. I intentionally roast a duck before the holidays so that I have plenty of fat for the crusty, delicious roasted potatoes that can only be achieved with this particular ingredient. French fries take on a light, crunchy texture that is unmatched (see recipe below).

Even a scant amount of fat in the bottom of pan or roaster can become the base of a lovely gravy. After you have removed your meat from the pan, put it over a medium flame and sauté a diced shallot or onion in a few tablespoons of the drippings. Whisk in a tablespoon or so of flour. Follow it with a splash of wine and continue to whisk in some stock and there you have it — gravy.


Duck Fat Fries

Duck, duck, frites! Duck fat fries are light and crispy. Because the fat doesn’t soak into the potato, they retain a fluffy, oil free interior. These are great as they are, but why not crank up the flavor a notch? A sprinkle of your favorite spice — I love seafood seasoning such as Old Bay on these — or some finely minced parsley or chives add a little color and flavor to the dish.

Some technical advice. Because temperature is the key to success in this twice-cooked method, it helps to have a candy thermometer to hit the bull’s eye. Also, you will need to have enough duck fat to fully submerge the fries as they cook. The amount will vary, depending on the shape of your pot. I like to use a medium saucepan and cook multiple smaller batches so I can use less oil. But if you have a lot of oil on hand or just a lot of mouths to feed, you can use more oil in a wider pan.


2 pounds starchy potatoes, such russet potatoes
2 cups of rendered duck fat, or more to fully cover potatoes as they cook
Salt and pepper
Seasoning such as dried herbs or spices (optional)
Malt vinegar (optional)
Minced herbs (optional)


  1. Tear open two large brown paper bags so they lay flat and set aside.
  2. Peel the potatoes fully or, as I prefer, in a zebra pattern of alternating strips of peeled and skin-on potato. Cut the potatoes into 1/4 inch to 1/2 inch batons and place in a large bowl. Cover the bowl with cold water and set aside for one hour, changing the water once. Drain the potatoes and dry them thoroughly and completely, using a towel to blot them.
  3. Lay one of the paper bags out on your counter. Heat the oil in a medium saucepan until it reaches 325 F. Add a handful of fries and cook until tender, about five to seven minutes. Using a slotted spoon or spider, remove the fries from the oil and strew across the paper bag to drain. Repeat with remaining fries. Allow to cool for five to ten minutes.
  4. Replace the bag with a fresh one. Raise the temperature of the oil to 375 F. Add a handful of cooked fries to the hot oil and cook for one minute to crisp them. Remove, as above, and strew across the clean bag to drain. Repeat with remaining fries.
  5. Sprinkle the fries with salt, pepper, any seasonings, vinegar or herbs you are using. Gather up the sides of the bag and jostle them a bit to evenly distribute seasonings. Serve immediately.

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