Reasons for Discarding Frying Oil and How to Test It

Reasons for Discarding Frying Oil and How to Test It

There are many ways to determine the discard point of your frying oil. Some are more accurate than others. To start, let’s take a look at the main reasons for discarding frying oil, and then we’ll review some options for testing it.

Reasons for Discarding Frying Oil:


Many experienced restaurant operators can determine when oil should be dumped by consuming a sample food item, such as french fries, potato cake, or a piece of bread. These items may have a crispy flavor at first, but as the food item becomes more digested, off-flavors or metal traces may overcome the initial taste. Some veteran operators will dip a piece of bread in oil as their method of testing oil quality.


Once food products begin to take on a darker color, oil discard becomes an obvious task. Customers will usually complain about the appearance of food before taste.


Rancidity can be detected with the appearance of smoke coming off the fryer. In extreme cases, this can lead to oil catching fire. If the oil is smoking, you are beyond the proper discard point and at risk of serving unsavory product.


If the oil smells bad, it is bad. Like smoke, if a bad odor is present you are beyond proper discard point.


Another quick test is the appearance of the fryer vat of oil. Some operators will determine oil discard based on the clarity of oil. If you can see through the oil, in some cases to the bottom of the fryer or enough to see the heating components, oil quality will be acceptable. There are a number of operators who will use a fry basket and simply submerge it enough to see through the oil.

How to Test Frying Oil

In addition to the sensory- and consumer-based benchmarks listed above, there are a few valuable tests that can determine frying oil discard points that are less subjective and more consistent:


The dark discard indicator can be changed based on your oil brand and product mix. Once the oil sample drawn with the middle oil dropper matches the dark side, it is time to discard.


The 3M Company manufactures paper strips, which detect FFA levels in used frying oil. 3M strips are carefully held with fingers or metal tongs and are dipped into hot oil for a second or two. The strip is then held in the air to view the number of bars. Once the fourth bar has discolored, the oil FFA level has reached over seven percent, and oil discard should take place. 3M strips have a shelf life of three to four months, and therefore, expiration dates must be checked. They must be refrigerated.


Total Polar Materials (TPMs) are quickly becoming the standard measure for fry oil quality. Testo and Ebro make digital measuring devices that measure TPM percentages. In Europe, oil is not to exceed 25 percent TPM. The wand end of the device is held in the hot fry oil until the reading settles on a number. Studies have shown TPM readings with these devices to be more accurate towards the end of oil life compared to the start.

Commit to an Oil Filtration Schedule

Accurate records are an important tactic for staying within compliance. Download the free Oil Maintenance Log from Filtercorp, and discover an easy way to track your oil maintenance program.


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