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How to Dispose of Used Cooking Oil

Avoid Pouring It Down the Drain

The Spruce / Catherine Song

Whether deep-frying, browning ground beef, or cooking bacon, we often end up with leftover cooking oil. The tendency may be to pour it down the kitchen sink but that can clog and damage the plumbing, and if it’s poured outside on the ground, it can cause problems for wildlife.

You can save your cooking oil to reuse later, but if it’s gone bad or you don’t want it, there some easy, safe ways to get rid of it. It’s also a good idea to check with your local solid waste department to see if they have any disposal recommendations or regulations.

Reuse Cooking Oil

If you plan to deep-fry soon or fry foods on a regular basis, you can save the cooking oil to use again. First, strain the oil through a coffee filter or several layers of cheesecloth to remove any particles and crumbs. Then, pour it into an airtight container and store in a dark place until ready to use.

It is important to note that you should reuse oil only once or twice. Give it a sniff before using it; if it smells rancid, toss it out. Remember that each time you reuse oil, the oil deteriorates and the smoke point (the temperature at which it will burn) decreases.

Pour Into Disposable Container

If you want to get rid of the oil, let the oil cool completely, then pour it into a nonrecyclable container with a lid and throw it in the garbage. Common nonrecyclable containers that work well include cardboard milk cartons and similar wax- or plastic-lined paper containers. Styrofoam and other takeout containers are also good options.

Chill Until Solid

If you prefer to throw it out, you need to freeze or refrigerate the oil first to harden it. Pour the oil into an old can and put it in the freezer or fridge. Once the oil is solid enough to come out of the can in one piece, it is ready to be thrown into the trash.

If you have no more than a cup of oil or grease, pour it into a coffee mug and set it in the fridge. When it solidifies, scoop it out and drop it into the trash with a spoon. Then wipe out the mug with a paper towel or used napkin before washing it.

Pour Small Amounts Into Trash

If you have a small amount of oil, it can be safely disposed into a partially filled plastic trash bag. Just be sure to cool the cooking oil first and close the bag. Paper towels, food scraps, and other absorbent material help contain the oil so you don’t have a pool of it that can potentially leak from the bottom of the bag.

Combine With Other Material

Before disposing, you can mix the oil with an absorbent material like cat litter, sand, and sawdust, which easily soaks up the liquid. Save old oil in a used container until it is time to empty the litter box; dump the oil into the litter before tossing out.

Purchase a Grease Disposal System

If you do a lot of frying, you may want to consider getting a grease disposal system kit that consists of a plastic receptacle with foil-lined bags that can hold up to 32 ounces of oil. Place a bag in the container and pour the cooled oil into the bag. When it is full, seal the bag and throw it in the garbage.

Recycle Cooking Oil

Some cities have collection programs for recycling used cooking oil into biodiesel. Check Earth911 to see if there’s a recycler near you that will accept it. Biodiesel is a clean-burning fuel that is used in many types of motor vehicles (often city trucks and fleet vehicles) and can be used as heating oil.

Cooking Oil Disposal Don’ts

There are a few no-nos when it comes to getting rid of used cooking oil. Don’t pour oil down the drain or in the toilet. It can clog not only your pipes but also the city sewer mains. You should also not add oil to a septic system. It can clog pipes and, even worse, your distribution lines and drainage field. Water contaminated with oil is difficult—sometimes impossible—to treat. This means it can eventually pollute local waterways.

Don’t pour hot oil into the trash can, as it can attract insects and rodents as well as cause issues with garbage trucks and solid waste sites. You should also not dispose of cooking oil into compost bins or piles. Fats, in general, are bad for compost, and cooking oil is nothing but fat.

There are several ways to properly dispose of cooking oil, none of which include dumping it down the drain.

Ask the Food Lab: How Many Times Can I Reuse Fry Oil?

Unraveling the mysteries of home cooking through science.

Our guide on how to reuse fry oil, and prolong its life.

[Photograph: Vicky Wasik]

How Many Times Can I Reuse Fry Oil?

I wanted to ask you today about reusing deep-fry oil. How many times can you keep reusing it until it goes bad? I remember you writing in your Wok Skills post that you can reuse oil until it becomes dark and somewhat bubbly. However, a popular Japanese TV show reported that a katsu made with old oil tasted superior to katsu made with new oil. I also read that many tempura places use a mix of old oil and new oil, which people claim adds a bit more flavor and color in comparison to using solely new oil.

—Sent by surcredibility

Whenever I post a recipe that includes deep frying, I receive a string of emails or comments asking me what to do with all the leftover oil after you’ve fried something. It’s a good question—nobody wants to throw out $10 worth of expensive peanut oil just to make a single batch of french fries.

There’s some good news, then some bad news, then more good news again, in that order.

What’s New On Serious Eats

Good News A: You don’t have to throw out used oil. Often you can reuse it many, many times!

Bad News: There’s no hard and fast rule for how many time you can reuse that oil. Distrust any source that gives a firm answer on the number times you can reuse oil.

Good News B: It’s easy to tell when you’ll need to replace your oil, and more importantly, there are some great steps you can take to increase the useful lifespan of your oil!

Let’s take a quick look at how deep-frying works before we go on.

Deep Frying Basics

Deep frying accomplishes two goals. First and foremost, it dehydrates foods. As soon as the food hits the hot oil, it begins to bubble. These bubbles are pockets of water that are suddenly vaporizing and jumping out of the food, heading up through the oil, and escaping into the atmosphere. The hotter you fry, the more vigorously these bubbles jump out, and the faster your food becomes crisp.

At the same time, the Maillard reaction is occuring: proteins and carbohydrates are breaking down and recombining to produce the browned colors and flavors that we associate with well-fried foods.

In order to prevent foods from becoming tough and stringy as they fry, most often fried foods are first coated with a protective insulating layer of batter or breading. This gives us the best of both worlds: tender, steamed food in the middle with a crisp, browned, bubbly layer of crispness on the exterior.

Incidentally, the folk wisdom that oil that’s too cool will cause foods to absorb more oil is bunk. In fact, because oil tends to move into spaces that were formerly occupied by water, the amount of oil a piece of fried food absorbs is directly related to the amount of moisture that is driven off, which in turn is directly related to the temperature you cook at, and the temperature to which you cook your food to. The hotter you fry, the more oil food will absorb.

The perception of greasiness is what increases with lower frying temperatures. Why? Because soggy fried foods that contain a mixture of oil and leftover water in their crust taste soft and greasy on the palate, even though the actual amount of oil they contain is lower than that of properly fried food.

What About Oil Freshness?

Does oil freshness really affect its ability to fry, and if so, how and why?

Oil’s freshness largely affects its hydrophobic nature. We all know that oil and water don’t want to mix, and this is one of the reasons deep frying works so effectively. You can submerge a piece of food in a pot of hot oil and not much oil will get absorbed—at least, not until enough moisture has been driven out of the food.

The more oil breaks down, the less hydrophobic it becomes. At first, this can actually be an advantage. Less hydrophobic molecules in your oil means that it can come into closer contact with foods, allowing them to fry just a bit more efficiently. This is where the wisdom of those tempura chefs comes in—adding a bit of degraded, old fry oil to the new batch will improve it.

Eventually, as this breakdown continues, your oil becomes less and less hydrophobic, and eventually it’ll start entering your food too rapidly, causing it to turn greasy and ruining its crispness.

At this stage, your oil needs to be replaced. Some telltale signs of old oil is foam on the top surface, an inability to reach frying temperatures without smoking, and a dark, dirty look and musty, fishy aroma.

The rate at which your oil will reach this stage depends on a number of factors. Let’s talk about those.

Things That Will Ruin Your Oil

So what factors will affect the number of times you can reuse your oil?

The Type of Frying Vessel

Sad reality: frying at home will ruin your oil faster than frying at a restaurant. Why? It has to do with the heating arrangement. In a dedicated restaurant deep fryer, the heating elements are raised above the bottom of the oil chamber. This creates a pocket of relatively cool oil at the very bottom underneath the heating element. As small bits of debris fall off of the foods being fried, they sink to the bottom of the chamber where they rest underneath those heating elements.

With a home setup, on the other hand, you end up frying in a pot or a wok placed over a burner. Particles of food fall to the bottom of the pan, coming in direct contact with a heat source and burning, imparting their flavor to the oil and hastening its breakdown.

Unfortunately, there’s no real way to avoid this unless you decide to purchase a dedicated electric deep fryer for your home kitchen. If you fry a lot, this is not a bad idea.

The Type of Coating

Basic rule of thumb: the more particulate matter you introduce to oil and the finer those particles, the faster your oil will break down. Battered foods like onion rings or bare foods like french fries will leave behind very little detritus after they’re done frying. Breaded foods like chicken cutlets will leave crumbs that fall off when the food is added to the oil. And foods dredged in flour like these Fried Fish Sandwiches will introduce a ton of particles.

So while oil in which you are cooking battered foods may last through a dozen or more batches, oil used for flour-dredged foods may break down after only three to four uses.

The Type of Food Being Fried

With battered and breaded foods, what’s inside doesn’t matter all that much as it doesn’t come into direct contact with the oil. But for foods that are fried bare, the type of food can affect the overall quality of the oil. Vegetables tend to dry the cleanest, imparting very little to the oil. On the other hand, fatty meats like chicken wings or bacon will render fat as they cook. This fat can then mix with your fryer oil, causing it to break down a little faster.

The Type of Oil and the Temperature

Different oils have different makeups in terms of their relative levels of saturated and unsaturated fats and other solids. This can affect the way they fry and the temperatures to which they can be heated. Generally, refined oils like most peanut, canola, vegetable, and corn can be heated to higher temperatures than raw oils like extra-virgin olive oil or most sesame oil. It’s not that you can’t fry in extra-virgin olive oil, it’s just that it will break down far faster than a refined oil—if it can even get hot enough to fry without smoking in the first place.

The best oils for frying tend to be those high in saturated fats, such as peanut oil, vegetable shortening, or lard. They’ll not only have the longest lifespan, but they’ll also produce the crispest results.

Storage

Oil can break down even without the energy of a burner underneath it. Its largest enemies? Humidity, light, and heat. You all have at least one friend who stores their oil right above the stove, or perhaps even sitting in a bottle against the backsplash. They are no-good, dirty rotten oil-killers and I urge you to de-friend them immediately.

Oils—even those that have been used a few times—should all be kept in tightly sealed containers in a cool, dark place.

How to Clean Oil

So you’ve cooked off that batch of fries, now you want to store the oil for future use. How do you do that?

Start by using a skimmer to skim off any floaters and large pieces of debris that might be lurking in the pot and discard them. Next, pour the oil through a fine mesh strainer into a clean, dry pot. If you were cooking flour-dredged foods, you may find a large layer of dirty, flour-filled oil at the bottom of the pot. Stop pouring before you pour this stuff through and discard it separately. Cover the pot with the strained oil to prevent dust from falling int, and let it cool completely. Finally, use a funnel to pour the oil back into its original container (you did save it, right?). Seal it tightly, and store the oil in a cool, dry place.

UPDATE: If you have some gelatin on hand, you can also give this gelatin-clarification technique a shot. It works like a charm and gives you crystal clear oil overnight.

Three Ways to Increase the Lifespan of Your Oil

  1. Use a Thermometer! Overheating oil is a quick and easy way to get it to break down into unusable form. At the same time, under heating oil before adding food to it will increase the amount of time that food has to sit there, which in turn increases the amount of particulate matter that falls off of it, which again can decrease oil lifespan.
  2. Work Clean! Keep a fine mesh strainer by your pot as you fry foods and use it to periodically clean up your oil by picking up and discarding any bits of batter or breading that may have fallen off your food.
  3. Stick with Battered foods or Bare Vegetables. Battered foods will impart far fewer impurities to the oil than breaded or flour-dredged foods. Bare foods like french fries or sweet potato fries even less.

Of course, even with all these tips, there are a crazy number of variables out there that can affect your oil. Your best bet for knowing when to toss the oil and when to reuse it is your own senses. Is it foamy? Does it smell rancid? Ditch it. Otherwise, just strain, store, and you’re good to go for the next fry-up.

Got a question for The Food Lab?

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J. Kenji López-Alt is a stay-at-home dad who moonlights as the Chief Culinary Consultant of Serious Eats and the Chef/Partner of Wursthall, a German-inspired California beer hall near his home in San Mateo. His first book, The Food Lab: Better Home Cooking Through Science (based on his Serious Eats column of the same name) is a New York Times best-seller, recipient of a James Beard Award, and was named Cookbook of the Year in 2015 by the International Association of Culinary Professionals. Kenji’s next project is a children’s book called Every Night is Pizza Night, to be released in 2020, followed by another big cookbook in 2021.

There’s no hard and fast rule for how many times you can reuse fry oil, but here are some ways to prolong the lifespan of your oil and identify when it needs to be replaced.