Why Cooking Oils Should Be Stored In Tightly Covered Containers

You might not spare too much thought on storing cooking and finishing oils. Most of us will just put them in the cupboard with all the other cooking essentials and forget about them. But the truth is, the way oil is stored can have a major impact on taste, freshness and overall quality. 

Cooking oils should be stored in a dark, cool place with a tightly covered container. That’s because heat, air and light exposure can all cause fat oxidation, deteriorating the quality of the oil.

What Is Fat Oxidation?

Oxidation is a chemical reaction that occurs when oxygen comes into contact with a substance, and is seen as a leading cause of food degradation. This has a particular affect on fat, and so fatty foods are particularly prone to this phenomenon. Cooking oils of all sorts are generally 100% fat, and so their shelf life can be drastically reduced by fat oxidation. 

Exposed fat becomes damaged or rancid with improper storage and care. This will cause the smell and taste to change and become much more off-putting, and there are health risks when it comes to consuming degraded, fat oxidized food,  such as an increased chance of heart disease. This particularly occurs in fats and oils that are high in saturated, fatty acids, since these aren’t as stable as more saturated fats.

Of course any food with fat in it will become rancid eventually but proper storage goes a long way to stave this off. Let’s look into some of the leading causes of fat oxidation so we know what to avoid.

What Are Some Of The Causes Of Fat Oxidation?

Air Exposure

Oxygen is noted within the very definition of oxidation as the main cause of the breakdown. Other factors can speed it up, but oxygen kicks the process off. This is why it’s very important that you keep the cap tight on your oil bottles. That will help prevent any unnecessary oxygen exposure and will thus go a long way to slow down the fat oxidation process. 

You can keep this same principle in mind with other fatty foods as well. Always keep the lid on tight if you have a container of butter for example, and never leave it exposed to the elements. Oily fish should be kept tightly wrapped as well, and doubling up on freezer bags are recommended when freezing them.

Light Exposure 

Light exposure is another thing that will speed up the oxidation process and therefore speed up the deterioration of the food. That means protection from light is another thing you should factor in when it comes to fatty foods, especially something 100% fat like a cooking oil. 

In fact, it’s even recommended that you take this into account when it comes to the tinting of their glass – dark brown or dark green bottles are stronger purchasing choices, when possible. Either way, definitely store the oil in a lightproof cupboards, rather than keeping them in some display cabinet. For the same reason, avoid leaving nuts and the like in jars on display.

Heat Exposure 

Heat exposure is another thing that can for sure speed up fat oxidation, which is not a good thing for anyone wanting to preserve the quality of food. Do not store your cooking oils, nor your spreads or anything else high in fat, near anything that creates heat. That means placing them a decent distance away from your oven, stove, hob or even a heater or something like that. That heat damages the fat.

That’s why solid fats should be stored in the fridge, never left on the table after a meal. For a cooking oil though, it’s good enough to leave it in a dark, relatively cool cupboard most of the time. In the event of particularly hot weather, you might want to consider storing them in the fridge as well though. 

Proper Storing Technique For Specific Cooking Oils

What we’ve said up to this point was speaking broadly, but now we’ll go into more specific notes for specific oils. 

Olive Oil:

You can think of olive oil as like a fresh fruit juice in the way you should be treating it. Oil pressed from an olive is very much perishable and doesn’t age like wine at all. Indeed, in addition to heat, oxygen and light, time is a major enemy for olive oil as well. When sealed, they can keep for as long as two years. But after they’ve been cracked open, get this; that shelf life shrinks to as little as two months! 

That really goes to show the difference that even brief exposure to light, heat and air can make. So yes, make sure that you’re going to be using up that olive oil fairly quickly after you’ve broken the seal on it. Be mindful of how much you expect to make use of it when buying olive oil. Bigger bottles are fine if you’re going to be making heavy and frequent use, otherwise maybe stick with smaller ones.

Dark bottles exist for olive oil, incidentally, and as stated above, it’s very much recommended that you go for those if you can. 

Coconut Oil:

Compared to other oils, coconut oil does pretty because it’s much higher in saturated fats than unsaturated fats. That means that it’s one of the more stable airs, and able to resist rancidity and fat oxidation. That doesn’t meant that we don’t recommend you take the same precautions as you would with any other oil, but it is nice to know that coconut oil should have a longer shelf-life, in theory. 

However one of those precautions that we spoke of was that, in the event of hot weather, storing cooking oil in the fridge is a decent idea. But here we see why it’s not advised to simply refrigerate cooking oil all the time to start with. Because keeping coconut oil in there for any stretch of time will alter the texture, causing the oil to harden. Great for no-bake applications, but obviously not idea for most uses of oil. 

Depending on what you hope to get out of coconut oil, it doesn’t seem like the fridge is the best place for it so stick to the cupboard if at all possible. And for sure discard it once it’s spoiled, which can easily be seen by a yellowish hue, a chunky texture and a bitter or sour scent. 

Sesame Oil:

Sesame oil on the other hand goes well in a fridge in general, in contrast to coconut oil. It doesn’t have the same risk of fully solidifying, but it is of course still as sensitive to heat, light and oxygen exposure as anything else. It too will end up turning rancid if improperly stored and that will invariably leave it with a bitter taste. 

So it’s best to keep it stored in the bottle it comes in and, in this case, the fridge seems to be a good option. Since there’s less to worry about in terms of hardening compared to other oils, keeping sesame oil in the fridge seems like a good idea, as it takes away all the risk of heat exposure. 

Safflower Oil & Other Vegetable Oils:

Safflower oil’s shelf life changes depending on if you keep it in the cupboard or in the fridge, and you may be surprised to know it lasts much longer in a dark, cool cupboard. Indeed it can last up to two years, although that might be assuming that it remains perfectly sealed for all of that time. Meanwhile, refrigerated it is said to have a shelf life of six months. 

Still it doesn’t harden in the fridge thanks to being packed with a high amount of polyunsaturated fat content. 

The storage advice for other vegetable oils is pretty similar, as they share a fair bit in common and oxidation can affect almond, avocado and canola oil in much the same way. It is worth noting that light isn’t as big a deal for oils that have been refined. That’s why vegetable oil often comes in clear plastic bottles, as there isn’t quite the same pressing need for a dark tint.

All the same, they should be kept in a cool, dark place and ideally not be anywhere near a stove.

Walnut Oil, Hazelnut Oil, & More

These are the most delicate of the cooking oils and so must be taken care of with a similarly delicate hand. Fancy nut oils including walnut, pistachio, truffle or hazelnut, along with whatever other infused oil you might have, have a very high amount of unsaturated fat content. They decline the quickest after opening and are the most likely to be brought down by oxidation. So it’s considered essential in this case to keep these oils refrigerated. It’s also very much recommended that you make use of them as soon as possible.

In Conclusion…

It feels like we may have beaten you over the head with it at this stage, but that’s only because it’s such a vital thing to understand. Heat, oxygen and light are the big things to fear when it comes to heavily fatty foods such as cooking oil. That’s why keeping them in tightly covered containers, in the dark and in a cool spot, is absolutely essential. There’s no other way to ward off fat oxidation.

Follow the steps we’ve provided and you should have no trouble maintaining your cooking oil for as long as you need it.