FER REPORT: All About Oil

Cooking oil is an organic compound like any other food, which means that over time it will break down and eventually spoil. How you treat it will determine how quickly that process takes place, affecting its useful frying life and ultimately, your profits.

Depending on their source, cooking oils may contain saturated fat, polyunsaturated fat, monounsaturated fat or a combination. Saturated fats contain only fatty acids that have been fully saturated with hydrogen atoms. Now that lard is rarely used (because of its high saturated fat content), cooking oil is sourced primarily from seeds such as corn, soybeans, sunflowers and rapeseed (canola), fruits (avocados, olives, etc.) and nuts (walnuts, hazelnuts, etc.). Some vegetable oils, such as palm, coconut and cottonseed oil, also naturally contain saturated fat, making them more stable than many unsaturated fat blends, but less “healthy."

In decades past, producers often partially hydrogenated vegetable oils (added a hydrogen molecule) to make them more shelf-stable. The hydrogenation process, though, produces trans fatty acids, also known as trans fat. In recent years, trans fat has been eliminated from most food products either voluntarily by producers or through legislation because of its links to potential health problems like cardiovascular disease.

When vegetable oils are fully hydrogenated, they turn solid. The good news is that they contain no harmful trans fat. The bad news is they’re fully saturated, and because they’re solid they’re difficult to work with. Oil producers now blend liquid oil with fully hydrogenated oil to make a more stable frying oil that’s easier to work with than solid shortening. 

Oils biggest enemies are air, water, food particles and salt, chemicals and detergents, trace metals from protein and blood, and heat. Three primary chemical processes cause oil breakdown: oxidation, hydrolysis and polymerization. Exposure to air causes oil to oxidize and go stale. Oil and water obviously don’t mix well; water in hot oil forms acidic compounds that affect flavor and odor. As oil begins to degrade, polymerization forms compounds that clump together, and those in turn hasten the formation of more compounds. Food particles as well as trace metals from protein and blood promote both oxidation and polymerization. Cleaning chemicals and detergents cause foaming and break oil down faster. And finally, heat accelerates all these processes.

Pick The Right Oil

The first step in making your oil last longer is picking the right oil for the task. Consider three main factors when evaluating different oils: the type of food you plan to cook, the flavor profile of the end product, and how healthful you want your menu items to end up. 

The type of food might affect whether you buy a heavier duty frying oil or a lighter oil. Breaded foods, for example, will quickly shed bits of breading and food particles into the oil and break it down more quickly, so look for a more stable oil, one that either has a higher percentage of saturated fat or a high-oleic content.

If you’re only cooking French fries, polymerization from food particles might not be a problem, but constant high heat can speed oxidation. Here you might want to look for an oil with a high smoke point (the temperature at which oil begins to burn and smoke). A number of operators cooking a high volume of French fries use cottonseed oil because of its high smoke point. 

Most vegetable oils are neutral in flavor and don’t impart much flavor to food. Others, however, such as olive oil, coconut oil and peanut oil, have a definite flavor, which might or might not complement foods cooked in them. Choose oils carefully when you’re looking for a specific flavor profile in your end product.

With a good oil management program you might be able to upgrade the oil you use from an all-purpose blend with a mix of poly- and monounsaturated fats (or even some saturated fat) to one with a more healthful profile, such as a refined canola oil with more monounsaturated fat, or newer high-oleic (Omega 9) or low-linolenic (Omega 6) oils that are very stable and high in monounsaturated fat. (Oleic fatty acids in oil helps prevent oxidation and has a positive health benefit; linolenic fatty acids speed oxidation and raise LDL or “bad” cholesterol levels in blood.) 

Use Best Practices

Slow the oxidation, hydrolysis and polymerization processes by using best oil management practices.

• Avoid filling fry baskets over hot oil, so food particles don’t fall in the vat. When cooking breaded products, skim the oil frequently with a wire mesh skimmer to remove food particles. Avoid salting foods over frying vats, too.
• Use fresh products, not frozen, whenever possible. Frozen products will release more moisture into the oil.
• Avoid cooking at temperatures above 360ºF. Oil starts degrading quickly at temperatures above 300ºF and temps over 360ºF start approaching smoke points for many oils. Reduce fryer temperature to 280ºF during idle periods to prevent it from deteriorating faster.
• Top off the vat frequently with fresh oil to keep the oil at the proper fill level.
• Filter oil regularly. Obviously, it’s difficult to take a fryer out of service when you’re in the middle of a rush, but the more often you filter your oil, the longer it will last. Most fryer manufacturers and oil processors recommend filtering about every fourth load if you’re cooking breaded products.
• Clean or boil out fryers only with manufacturer-recommended cleaning products. Be sure to completely remove all traces of any cleaners and dry the vats thoroughly before refilling with oil.
• Cover fry vats when not in use to keep oil from oxidizing and to prevent food or dirt from getting into the oil.

Filter Properly

Proper filtration doesn’t just mean filtering oil regularly. There are two types of filtering—passive and active—and a variety of filter media to use depending on the product you’re cooking in your oil and what you’re trying to accomplish.

Passive filtering involves passing the oil through a filter medium to remove particulate matter. Common filter media include stainless-steel mesh, paper and fabric, and can remove particles ranging in size from 300 to 0.5 microns. 

Stainless filters are easy to clean, but only remove large food particles. Paper filters are inexpensive, but can clog or gum up quickly and absorb a lot of oil, costing you money in the long run. Fabric filters can be reused over and over and can remove the smallest particles. Carbon, another passive filter medium, also removes volatile compounds that cause off flavors and odors. You might end up using carbon along with another medium for best results depending on the product you’re cooking.

Active filtering uses a chemical filter powder to remove protein, blood and other impurities from oil that passive filters might miss. This often is referred to as “polishing” the oil, a step you usually need to take only if you’re frying products like meat, seafood and poultry. 

Know When To Say Goodbye

Even if you filter your oil regularly, eventually it will deteriorate to the point that continuing to use it will result in bad tasting, poor quality products. Throw it out too soon, however, and you’re wasting money. So when’s the right time to dispose of it?

You can use three methods to test or evaluate your oil. Color is one way operators judge how old and used up oil is. Though color kits can make this method less subjective than simply eye-balling a fryer vat, an oil’s color doesn’t tell you the whole story. 

The next best method is a chemical test strip that turns color when dipped in the oil. Test kits include color-matching charts that let you know whether the oil still has some life left in it.

The best way to evaluate oil quality is to measure what’s called total polar materials (TPM) in the oil. A TPM of 25 or more indicates that it’s time for an oil change. Bi-metal sensors similar in appearance to digital thermometers give you an accurate read on TPM content in your oil usually in about 20 seconds. Though more expensive upfront than test strips, the device is far less expensive over time, and more accurate. 

Always filter your oil before you test it. You’ll get a more accurate read of how much life is really left in it. And even if it’s time to retire it, filtered oil is more valuable to recyclers than dirty oil.

SIDEBAR:

Oil Smoke Points

At a certain temperature, oil will begin to break down into its individual components, and the free fatty acids that are formed begin to burn and smoke. The more free fatty acids an oil has, the lower its “smoke point.”  Though there are some general ranges at which different types of oils smoke, each is unique, so generalizing an exact smoke point for, say, canola oil is impossible. That said, here are approximate smoke points for a variety of oils.

Oil                   Quality                        Smoke Point

Avocado oil    Refined           520°F              271°C

Canola oil        Expeller Press  375-450°F       190-232°C

Canola oil        High Oleic       475°F              246°C

Canola oil        Refined           400°F              204°C

Coconut oil     Refined           450°F              232°C

Corn oil           Refined           450°F              232°C

Cottonseed oil                         420°F              216°C

Grapeseed oil                          420°F              216°C

Hazelnut oil                             430°F              221°C

Lard                                        370°F              188°C

Olive oil          Extra virgin     375°F              191°C

Palm oil           Difractionated 455°F              235°C

Peanut oil        Refined           450°F              232°C

Rice bran oil                            415°F              213°C

Safflower oil   Refined           510°F              265°C

Sesame oil       Semirefined     450°F              232°C

Soybean oil     Semirefined     350°F              177°C

Sunflower oil  Semirefined     450°F              232°C

Walnut oil       Semirefined     400°F              204°C