Combining oil and dried tomatoes or basil to create mouthwatering Mediterranean condiments has become commonplace. Herbs and garlic are also frequently mixed with olive oil to make herb-infused oils for cooking. It may be surprising to realize that while oil slows spoilage on some food, it should be used cautiously when preserving raw food.
Oil does not safely preserve raw food. Adding oil to fresh produce prevents oxidation and discoloration but does not stop the natural deterioration process. Oil does not destroy bacteria that may be present in the food. Raw herbs and vegetables stored in oil must be refrigerated.
Food coated in a film of oil may look appetizing and safe to eat, but it is not safe for all types of food. Find out what foods you can preserve in oil and how long the food preserved in oil is likely to last.
Can Oil Preserve Food?
Plunging food into oil creates an oxygen-free environment, which may sound ideal, but unfortunately, the anaerobic conditions are perfect for the growth of bacteria. One microorganism that thrives in an oxygen-free environment is the dreaded Clostridium botulinum, more commonly known as botulism.
Storing raw herbs or vegetables in oil does nothing to stop the growth of bacteria that may be present in the food. This is particularly true in low-acid food like eggplant and mushrooms. Without using other methods to keep these ingredients fresh, they would quickly become unsafe if they were only preserved using oil.
To safely preserve food in oil at room temperature, food should be processed using another preserving method before being packed in oil. An excellent example is dried tomatoes, which are naturally acidic and safe to store in oil, but only after they are fully dried.
Another way to safely store food in oil is to prepare and freeze the oil-infused recipe. A delicious method to store basil is to create an oil-infused pesto that can be frozen in ice cube trays and used when required.
Whole, fresh vegetables like carrots, peppers, and herbs can be stored in oil, but they should be refrigerated and used within four days. According to a research paper released by Oregon State University, household refrigerators are often not cold enough to safely preserve food stored in oil for long periods.
Commercial garlic mixtures are commonly acidified using brine or vinegar before being stored in oil to prevent discoloration. While it is not a good idea to use oil on its own to preserve fresh produce, it can be effective when used in conjunction with other preservation methods to retain color and keep food looking appetizing.
How Does Oil Preserve Food?
The oil preserves food for short periods by eliminating one of the elements responsible for food spoilage, namely oxygen. Since the oil on its own doesn’t eliminate any bacteria from food, and other necessary conditions for food deterioration, including light and temperature, may be present, oil on its own should not be considered a safe way to preserve food.
Food can be preserved in oil if it is processed using another method before being sealed in an airtight container or kept inside the fridge. Common ways to ensure food safety before it is added to oil are pickling, brining, cooking, or drying to eliminate harmful bacteria that may be present in food.
Preserving Food In Oil
Foods commonly preserved in olive oil include peppers, mushrooms, cheese, herbs, olives, eggplant, and tomatoes. The delicious oil not only protects the surface of the food from spoilage caused by oxidation, but the oil itself takes on the delicate taste of the food and can be used later in other recipes.
Two methods are commonly used to eliminate bacteria on food and render it safe before preserving it in oil:
- Soaking vegetables or herbs in a vinegar solution: The most common method of making fresh vegetables and herbs as safe as possible for storage in oil is first to soak produce in a vinegar bath. Vinegar has been used as both a flavoring and a food preservative for thousands of years, and its naturally high acidity will kill any bacteria on the surface of produce.
- Dehydrate the produce to be stored: Food that will be preserved in oil should be dried close to crispness to ensure that harmful bacteria are destroyed.
Note that although these methods will eliminate botulism-causing bacteria, food spoilage could still occur due to other factors. Food could, therefore, still spoil if preserved in oil, but it is unlikely to be toxic.
Does Oil Go Bad?
It may be surprising to many to realize that oil, even on its own, can go bad. Even unopened bottles of oil can become rancid with time, so to make oil last as long as possible, it is best to store it in a cool area or, even better, in the fridge.
Oil stored in cool conditions is more likely to stay tasting fresh for longer. Always check the expiration date of oil because, like any food, despite its oily texture, it does go off.
Different types of oil will last for varying lengths of time. Virgin olive oil is one of the longest-lasting varieties. Other varieties, like grape seed oil, must be used within three months or can be refrigerated for a maximum of six months.
Regularly check the texture and odor to tell if your oil has gone off. Oil that has become rancid develops an unpleasant smell that is easy to detect.
The best way to store oil is in airtight containers in a cool environment. Refrigerating may change the texture, but the oil will revert to liquid when it is back at room temperature.
Can I Can Food That Is Preserved In Oil?
Very few research-tested recipes include significant amounts of oil for canned food. Canning food containing oil is tricky since oil has unique properties that make it react to heat processing differently than most other foods.
It is essential never to create your own homemade recipes if you intend to pressure can or hot water bath your canned food. There are three main reasons why canning food preserved in oil is not a good idea:
- Oil goes off and becomes rancid over time. When this happens, the oil changes taste and will spoil the flavor of your canned food.
- Oil can superheat and rise up during the canning process. This is highly likely to interfere with the seal on your jar. If you are canning food containing oil, you must leave plenty of additional headspace in each jar.
- Oil has unique properties which can lead to heat processing interference during canning. Fat molecules in the oil tend to shield bacterial spores from the intense heat during processing. That means that despite your best efforts, a few could slip through and multiply in the food.
What Oil Is Good For Preserving Food?
Not all food-preserving oils are created equal, and some are better than others for adding to food to keep it tasting good. Olive oil has been the preferred choice for preserving food for centuries, but plenty of alternative options are now available.
When preserving food using oil, it is a good idea to select a mild-tasting variety that will complement the flavor of the ingredients. Popular choices include olive, sunflower, sesame, and grapeseed oil.
Oils to avoid include highly processed varieties like canola, soybean, and corn oils. Although these are often less expensive than olive oil, they won’t deliver the same flavor profile and may not offer the same health benefits as olive oil.
One of the downsides to using olive oil is that it can be expensive compared to many other oil options. To safely preserve food using oil, food must be completely covered to prevent contact with air.
How Long Can You Preserve Things In Oil?
Preserving food in oil is not the same as canning, so food will not be shelf stable. All food preserved in oil, with the exception of plain dried tomatoes, must be stored in a refrigerator and have relatively short best-by dates.
There is no set answer to how long food preserved in oil will stay fresh. The best-before dates are variable and based on the individual ingredients, other preservatives added, and the recipes used.
Let’s go through some simple oil-based recipes that will give you some idea of how long fresh vegetables and herbs will last when preserved with oil.
|Recipe||Ingredients||Method||How long will it last?|
|Roasted vegetables in olive oil (this can include beets, roasted peppers, grilled zucchini, tomatoes, etc.)||2 parts olive oil1 part vinegar Salt and pepper||Cook all vegetables. Submerge veg into the marinade and store in sterile jars in the refrigerator.||It can last 3-4 months in the refrigerator if veggies stay submerged. Note: The mixture must not contain ANY raw items like herbs or garlic.|
|Raw garlic or herbs in oil||Fresh garlic or herbsOil to cover||Cover herbs or garlic with oil and refrigerate||Use within four days. The mixture can also be stored frozen.|
|Dried tomatoes in oil (Note: this recipe only includes dried tomatoes, without fresh herbs or garlic)||Dried tomatoes Oil to cover Dried herbs can be added||Cover fully dried tomatoes in oil. This solution does not need to be refrigerated; however, keeping it in the fridge will delay the oil becoming rancid.||This oil-based recipe is one of the few that can remain shelf stable at room temperature for as long as the oil stays fresh.|
|Mushrooms or chilies in oil||Fresh mushrooms or chiliesOil to cover||Cover fresh ingredients with oil and store in the refrigerator or freeze.||It will last in the fridge for four days. Coating these ingredients in oil works well for long-term freezing.|
The oil preserves food by preventing oxidation. This makes coating food in oil an excellent way to maintain the color of ingredients. However, oil is not a reliable way to conserve food for long-term storage. Raw food could contain dangerous bacteria that thrive in anaerobic conditions, so it is recommended first to process food using other preservatives like salt or vinegar before submerging it in oil.