Deep Fryer Oil: How Long Before It's Trash?

Deep-frying is a great way to cook food, but it can be a messy and costly process. One way to save time and money is to reuse frying oil. However, it's important to know how long you can keep the oil and how to store it safely.

The length of time you can keep deep fryer oil depends on several factors, including the type of oil, the food being fried, and how the oil is stored. Oils with a high smoke point, such as peanut, canola, or vegetable oil, are ideal for deep frying and can be reused multiple times. On the other hand, extra-virgin olive oil has a low smoke point and is not suitable for deep frying.

To prolong the life of your frying oil, it's crucial to control the temperature and avoid overheating. Oil should be stored in a cool, dark, and airtight place, preferably in a sealed container in the refrigerator. It's also important to filter the oil after each use to remove any impurities and food particles.

Signs that your frying oil needs to be replaced include a dark colour, a rancid smell, foam on the surface, and an inability to reach frying temperatures without smoking.

By following these guidelines, you can safely reuse deep fryer oil and save time and money.

Store oil in a cool, dark place

To keep deep fryer oil for as long as possible, it's important to store it in a cool, dark place.

Oil is sensitive to light and heat, so it's best to keep it away from sources of heat, light, and humidity. Store the oil in a cool, dry, dark place that is not above the stove, oven, fridge, or microwave. A tightly sealed container is ideal for storing oil, and it can be kept in the original oil container or a glass jar.

If you're storing oil in a deep fryer, make sure the fryer is tightly shut and in a location that is dark and cool.

Additionally, it's important to note that the more food you fry, the darker the oil will become. If the food you are frying becomes dark too quickly, it is an indication that you should change the oil. Frying foods in unhealthy oil can be unsafe.

By storing oil in a cool, dark place, you can help extend its shelf life and keep it usable for longer.

Oil's lifespan depends on food type, straining, and oil type

The lifespan of oil depends on several factors, including the type of oil, how it is stored, and what foods are cooked in it.

Oil Type

Oils with a high smoke point, or the temperature at which the oil starts to break down and produce smoke, are ideal for deep frying. Examples include peanut oil, canola oil, safflower oil, and vegetable oil. Oils with high levels of monounsaturated fats, such as canola or peanut oil, are more heat stable and better suited for deep frying. Oils with high levels of polyunsaturated fats, such as canola oil, are less suitable for deep frying as they can react with oxygen and form harmful compounds when exposed to high heat.

Straining and Storing

To extend the lifespan of oil, it is important to strain and store it properly between uses. This involves allowing the oil to cool, straining it through a cheesecloth or coffee filter to remove any solid particles, and storing it in a sealed, light-proof container in a cool, dark place. With proper maintenance, oil used in a busy restaurant should be changed once or twice a week, but this can vary depending on the type of food being fried and the temperature at which it is fried. For home use, oil can be stored in the deep fryer if it is thoroughly heated before each use, or it can be stored in a separate container in the refrigerator.

Food Type

The type of food being cooked can also impact the lifespan of the oil. For example, cooking fish in oil can cause a slight odor that may be difficult to remove, even after straining the oil. Some foods may also be more likely to cause the oil to break down or oxidize, leading to a decrease in quality and lifespan.

Oil can be reused if filtered and stored correctly

Filtering

Filtering oil after frying is important to remove any impurities, such as loose crumbs or sediment. This is especially important if you're frying anything breaded or battered, as these particles will burn the next time you heat the oil. To filter the oil, wait until it has cooled to a safe handling temperature, then drape a few layers of cheesecloth or a coffee filter over a fine-mesh strainer or chinois set over your storage container. Pour the oil through the cheesecloth or filter to catch any crumbs, then store the filtered oil in an airtight container.

Storing

Oil should be stored in a cool, dark place, such as the refrigerator or freezer. Oil can be stored in the deep fryer if it has an airtight lid, or it can be transferred to a sealed container such as a glass jar or its original bottle. Stored oil should be used within one to two months.

Other Tips

• The type of oil matters. Peanut oil, canola oil, and vegetable oil have high smoke points, making them good choices for deep frying. Extra-virgin olive oil, on the other hand, has a low smoke point and a strong flavour, making it less suitable.
• Temperature control is key. Oil should be carefully maintained below its smoke point to prevent the breakdown of fats, which can cause a bitter taste.
• The type of food being fried matters. Battered foods, such as onion rings, will leave behind fewer impurities than breaded foods, such as chicken cutlets. Vegetables tend to fry the cleanest, while fatty meats like chicken or bacon can cause the oil to break down faster.
• Skim and strain the oil after frying to remove any large pieces of debris and loose particles.
• Label used oils with the food they were used to fry to prevent flavour overlaps.

Oil's breakdown is indicated by foam, smell, and colour

Oil breakdown is indicated by foam, smell, and colour.

Foam

Foam in oil is caused by volatile and non-volatile compounds that form when oil deteriorates. Non-volatile compounds remain within the oil, producing polymerisation at temperatures above 200°C (390°F) or in isolated hot spots within the frying system. These molecules bond together to form large, different-sized clusters that accumulate on the oil's surface and, because they don't dissolve, they cause foaming. Foaming traps air under the oil and increases the possibility of hydrolysis.

Smell

Our sense of smell is a very direct sense. In order to smell something, molecules from that substance must find their way to your nose. These molecules are mostly small, light, volatile chemicals that find their way into your nasal passages. Once in the nasal passages, these molecules come into contact with a special patch of neurons with hair-like projections called cilia that increase the surface area to capture more of the molecules. The molecules attach to the cilia and trigger the neurons to send a signal to your brain, which causes you to perceive a particular smell.

There are several smells that indicate oil breakdown:

• Oxidation has a sour or pungent odour, similar to rotten eggs.
• Thermal failure smells like burned food.
• Bacteria can produce a road-kill smell or stench.
• Sulfur compounds have a skunk-like odour.
• Nitrogen compounds have an almond-like scent.
• Esters and ketones have a perfume (fruity) odour.

Colour

New, clean oil is amber in colour. As engine oil gets darker, it can indicate high heat, contaminants, or the presence of additives that cause the oil to darken during normal use. However, oil can be very, very dark (black even) and still be effective. Therefore, the best way to determine if the colour of your oil indicates a problem is to observe how it changes colour over time.

Oil should be stored in a sealed container

When storing oil, it is important to seal the container tightly to prevent oxidation, which occurs when oil comes into contact with air. Oxidation can cause the oil to become tainted or acidic, affecting its taste and quality. Additionally, light and heat can accelerate the breakdown of oil, so it is best to store it in a cool, dark place.

The refrigerator is an ideal location for storing oil, as it provides a cold, dark, and airtight environment. If you plan to store the oil for an extended period, consider freezing it. Freezing can further slow down the breakdown process and extend the oil's shelf life.

Before storing, it is crucial to filter and strain the oil to remove any impurities, such as food particles or sediment. These impurities can cause the oil to become rancid and affect its taste and quality over time. Using a fine-mesh strainer or cheesecloth, strain the oil into a clean, dry container before sealing and storing it.

By following these storage guidelines, you can prolong the life of your deep fryer oil and ensure that it remains safe and suitable for future use.

Frequently asked questions