This article explores which is the best method for checking oil quality: TPM (Total Polar Materials) or FFA (Free Fatty Acids)?

At Klipspringer, we’ve been helping manufacturing and hospitality businesses to ensure food compliance for over 20 years. 

By removing all guesswork from food oil management, we’ve modernised food safety for the likes of:

  • McDonalds
  • Whitbread
  • Chopstix
  • Wasabi
  • Five Guys.  

During this time, one of the most frequent questions we have received from our customers has been: which method of checking oil quality is most accurate, compliant, and objective? This article aims to answer that question, addressing a much-contested area of food oil management: the TPM (Total Polar Materials) vs FFA (Free Fatty Acids) debate.

Oil Quality

Why does frying oil need testing?

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.  

Oil Quality

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 Research has shown that, surprisingly, most businesses prematurely discard usable oil due to basic or outdated testing methods.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.  

What are the most common oil testing methods?

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, along with the 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.  

Oil Quality

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.

Oil Quality

Dielectric constant-based methods are also less likely to be single-use, unlike test strips, which result in an ongoing cost of around £300 per year.  

Overall, FFA Measurement is still a reasonable solution for food oil monitoring, but isn’t particularly ground-breaking given modern technological advances. As explained above, there is nothing inherently wrong or non-compliant about it. But, for businesses seeking to go the extra mile, other more innovative options are out there.    

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.  

Best used at the end of each trading day, when the oil is still hot, Food Oil Monitors are efficient and fast to operate. Kitchen staff simply have to place the sensor stem into the vat of oil, and then use a gentle stirring motion until the light at the top of the instrument begins to flash. If the Monitor flashes green, the oil is safe to use again. If it flashes amber, the oil needs changing soon. If it flashes red, the oil requires immediate changing.  

For smaller establishments, a potential drawback of Food Oil Monitors is the upfront cost – usually in the region of around £470. However, once purchased and implemented, the Monitors typically show a return on investment within six months, and should last for three or more years. What’s more, these Monitors can be specifically calibrated to various oil types, and are able to verify temperature, as well as oil quality.  

Oil Quality





Visual Inspection

Simple eye test based on oil colour

  • Speedy

  • Inaccurate

  • Dependent on individual judgement

  • Lack of product integrity & consistency

FFA Measurement

Uses test strips and a colour chart to measure Free Fatty Acids

  • Relatively accurate (around 80%)

  • Compliant

  • Single-use (£300 per year in ongoing costs & wastage)

  • Subjective to inadequate or distorted lighting

  • Contaminated by improper storage

TPM Measurement

Uses a Food Oil Monitor to measure Total Polar Materials

  • Uses the dielectric constant for high accuracy

  • Compliant

  • Objective

  • ROI within 6 months

1. Upfront cost of around £470

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. If you want to quickly outline each oil monitoring method’s pros and cons with your team? Refer to the above table for a concise overview. Plus, for an example of how Food Oil Monitors have helped companies increase compliance and cut oil usage, read about Whitbread’s savings of up to 52%. 

You can also contact us on 01473 461800 or Alternatively, you can use the form below to arrange a free consultation.  

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