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When you fry foods, the foods leave pieces behind that cloud up the oil. Skimming the oil takes away some of these pieces, though you'll need to take further steps to remove all of them. Skimming the oil just takes care of the big pieces. Use a skimmer to get rid of any floating pieces of food that are on top of or inside the blackened oil in the pot. Throw them away. You can also use a skimmer to clean the oil while you're cooking. You can buy oil skimmers at most big-box stores that have household items. Oil skimmers are pretty cheap. You can get one for about $12 or so, and you can also buy them online or at a restaurant supply store. They are a metal mesh net circle fastened to a handle. After you use a skimmer to remove the larger pieces, you need to strain the oil next. Straining the oil removes the smaller bits of sediment, so your oil is less cloudy overall and you don't have bits of food left in it. You'll need a fine mesh strainer or cheese cloth for this process. Wait until the grease is cool to strain it. Have a clean pot or bowl ready. Pour the grease through the fine mesh strainer. Make sure not to pour too fast and overflow the strainer. Also, if you see sediment in the bottom, don't pour the last of the oil in. Leave the sediment where it is, and toss it later. If you don't have a strainer, try cheese cloth over a funnel. You can also try coffee filters. If it's hard to pour, use a measuring cup or large ladle for the straining process by straining a little bit of the oil at a time. Once you've strained the oil, get the original container back out. Use a funnel to pour the oil back into it. The original container was designed to store the oil, so it's fine to use it again. Just make sure you don't pour hot oil into a plastic container. Only use the original container if you used all of the oil in it to deep fry. Otherwise, you'll be adding used oil to new oil. Don't place the cover on the container until the oil has completely cooled. It's not just cooking that breaks down oil. How you store it can also break it down. You need to keep the oil away from humidity, light, and heat to keep the oil in prime cooking condition. Light and heat will further degrade the oil as it sits in storage, increasing the chances you can't reuse it. Do not store the oil above the stove, where it will be subjected to secondary heat from other cooking. Instead, store the oil in a cool and dark location. The refrigerator is a good choice if you have room. Oil in the refrigerator will be thicker and may look cloudy (white), but it will be fine once it comes to room temperature. Keep in mind that once cooking oil is used, it is going to harbor some of the smells of the food you last used in it. For example, cooking fish in oil will impart its flavor to the oil, so you only want to fry fish or other proteins in it, not something sweet. Keep your oils separate. If you used one for cooking fish, put it in its own bottle so you don't use it to cook something sweet. Label each bottle of oil with what you cooked in it, as well as the date you bought it or last cooked with it. Reusing used cooking oil can make a lot of sense financially if possible. For example, the peanut oil used to make one batch of French fries can cost as much as $10. Just because you used the oil for deep frying the first time doesn't mean you have to use it for deep frying the second time after cleaning it. You can use it to cook in other ways, such as making a stir fry. You can also use the oil to bake. Remember, again, that the oil will retain some of the flavors and smells of the first food it was fried in, though, so always use it with similar flavors.
Skim the oil. Strain the oil. Pour it back into the container if it's empty. Store the oil. Reuse the oil with the right foods. Reuse your cooking oil for other purposes.