What is the Best Way to Check Oil Quality?

Frying produces exceptionally flavoursome food. It is an inexpensive, rapid, and popular way of cooking, which delivers the ultimate food sensory trifecta of “golden, brown, and delicious”, or “GBD”.  

However, this trifecta is only guaranteed if the food in question is fried in safe, high-quality oil. Past a certain level – where the oil is not brand new, but rather from B-C on the below graph – this quality is jeopardised by the repeated use of oil, which causes it to degrade. When oil is used continually, an increasing number of chemical reactions occur, leading to alterations in its composition.  

As cooking oil degrades, so does the taste, texture, and overall flavour of the food. For manufacturers and hospitality businesses that prioritise product consistency, this can be a pressing issue.  

Product integrity is another area compromised by flawed oil management processes. In the worst-case scenario, it can expose customers to the build-up of acrylamide – a cancer-causing chemical.  

On the other side of the coin is oil wastage. Research has shown that, surprisingly, most businesses prematurely discard usable oil due to basic or outdated testing methods. Amid astronomical rises in oil prices, a growing number of restaurant operators are arriving at the same conclusion: monitoring oil quality ensures compliance, prioritises sustainability, and significantly cuts costs. The only question remaining is how best to do it.  

Currently, there are three predominant oil testing methods used in the industry. The first is simple, but amateurish. The second is relatively accurate, but subjective. The third is eco-friendly, cost-saving, and entirely objective.  

Read on to learn about the core differences, pros, and cons of each method.   

Method #1 – Visual Inspection 

Unfortunately, many restaurants still change their oil based on a quick visual check. While some chefs with vast amounts of experience can make informed guesses about when to change their oil, their decision is still subjective. It stems from the “we’ve always done it that way” rationale which has come to harm many businesses over the years, whether it be through unnecessary expenditures, unsustainable practices, or audit non-conformances.  

In this day and age, taking a quick glance at a batch of cooking oil and deciding if it’s safe simply doesn’t cut it. This is twofold: the rate of darkening differs from oil to oil, and is also dependent on filtering practices and product types. Overall, visual inspection is better than no method of oil monitoring, but there are more accurate options available.  

Method #2 – FFA Measurement (Test Strips) 

High levels of FFA, or Free Fatty Acids, directly correlate to off-colours, off-odours, and off-flavours in fried food products. FFA is typically measured using test strips. After being dipped into the oil, a range of colours appear on the strip. This is then compared to a colour reference chart to determine FFA levels. Standard test strips measure free fatty acid levels from 2% up to 7%, with 5.5% to 7% as the discard range.  

So, just how effective are FFA Test Strips?  

With an overall accuracy of roughly 80%, these strips offer greater compliance than any visual inspection, but don’t provide the same assurance nor peace of mind as other methods. This is primarily because the comparison of the strips’ colouring with the colour chart is still subjective to inadequate or distorted lighting, and strips can also easily be contaminated by improper storage.  

Studies have found that monitoring methods based on dielectric constant provide more “objective and valuable results” than those based on colorimetric reactions. In other words, methods that go beyond surface-level colouring – outlined below – are more reliable.

Method #3 – TPM Measurement (Food Oil Monitors) 

Devices which determine cooking oil quality by TPM, or Total Polar Materials, remove the subjectivity found with previously summarised methods. By basing data on changes in the dielectric constant, handheld TPM devices – usually a Food Oil Monitor – are greater in accuracy than FFA-based methods.  

TPM Measurements is the most current method utilised in commercial kitchens. Legislatively encouraged across Europe, the go-to critical parameter for TPM limits falls between 24% to 27%. A TPM reading of higher than 25% is considered the discard point in many European countries.  

Hopefully this summary has given you a structured insight into the best ways to check oil quality, and has provided some clarity in settling the age-old debate between FFA and TPM.