Extending the frying oil shelf life whilst maintaining product food safety and quality is one of the goals of food service operators. Filtering the frying oil regularly is by far the most important recommendation to achieve it.

Besides filtering, there are 2 other procedures restaurants follow to try to extend oil life, named frying oil cascading (rotation) or “cradle to grave”.

Frying Oil Cascading

is the procedure where the frying oil is transferred from one vat to another, until it is deemed unfit for use as per food service operator quality standard procedure or legislation.

“Cradle to Grave”

is the method of keeping the frying oil in the same vat that point is reached. 

The oil degrades at different rates in the fryers vats when frying different types of food. When operators use cascading, oil is moved from a Vat with lower debris, lighter oil color (less “hostile” frying oil environment) to Vats with higher debris and darker oil color (more aggressive circumstances).

From experience, the frying oil life is maintained better when the “cradle to grave” operation is followed. There are some technical explanations that could support the preference for the “cradle to grave” approach.

Below are the advantages of it:

• No risk of frying oil contaminants being transferred from one frying vat to another.
• Less risk of allergens and off flavors cross contamination among products.
• No work involved in transferring the fryer oil from one vat to another.
• Easier to control frying oil service shelf life via frying oil quality parameters.

By working with the cradle to grave practice, the frying oil is allowed to run its normal degradation course and be discarded when the end point frying oil quality parameter is reached, thus maintaining a longer fry-life.

Therefore, it is always a good practice to maintain cradle to grave approach in restaurant fryer operations to obtain longer oil fry-life and avoid product food safety and quality issues.

The quality of fried food is highly linked to the conditions of frying oil. Although there is not one specific worldwide regulation for frying oil quality, several countries have adopted guidelines or created regulations for the matter. Most of them are based on studies done regarding frying oil stability during cooking and possible deleterious effects in human health.

Nowadays, Total Polar Compounds (TPC) or Total Polar Materials (TPM) is the most common frying oil parameter. These are the most reliable to determine the oil quality, according to the German Society for Fats Science (DGF). The TPM value provides information on the quantitative proportion of polar and non-polar compounds in cooking oil. In Europe, determining the TPM value has become the standard reference protocol.  For assessing the fats and oils quality in deep-frying conditions in foodservice, it is one of the best quality indicators. As a result, several countries have set the limits of 24 to 27% TPM for degraded frying oil. In countries such as the USA and Australia, where TPM is not a legal limit value, the parameter is becoming increasingly used by foodservice operators as an internal benchmark.

Some countries use acid value (AV) or free fatty acids (FFA) as quality standard. According to American Oil Chemists’ Society Official Methods and Recommended Practices, FFA is obtained dividing AV by the factor 1.99.

Below are some countries with guidelines or regulations in place to determine frying oil quality for Foodservice.

Frying oil degradation is a very complex process. It involves several chemical and physical reactions between the frying medium and the product. During frying, physical changes occur, such as heat being transferred from the heating elements to the frying oil and consequently from the oil to the food. Heat causes water in the food to evaporate and reacts with the frying medium.

In addition, there are several chemical reactions occurring among food, frying medium and air. These interactions, influenced by the frying oil, food types as well as frying conditions and oxygen availability are interrelated and produce a complex mixture of substances. The chemical reactions frying oil undergoes are oxidation, hydrolysis and polymerization.

Frying is a popular method of cooking because it is quick, easy and usually results in delicious food.

During the frying process cooking oil is being exposed to heat and all kinds of contaminants (breading, batter, crumbs, marinades, ice particles from frozen food etc.) reducing its lifetime. To extend frying oil service life filtration is the most important step. It helps to control consistency of food and keeps operational costs down.

These are the common methods applied to frying oil.