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Seven enemies of Frying oil, Fish and chip shop, title

You cannot run a fish and chip shop without frying oil in tip top condition. After all, our favourite fish and chips have to have that crisp, golden texture. 

There are enemies of frying oil that can degrade it, reducing its longevity and causing havoc with the foods it contains. Identifying the culprits that are causing breakdown is the most important step in ensuring proper maintenance of your cooking oil and enhancing food quality. The results are happier customers and the ability to maximise profits by enabling your oils to last longer.

Here’s a look at the seven enemies of frying oil that might be costing you that return customer.

Oxygen is present in the air around us. When edible oil reacts with oxygen, it forms hydroperoxides through the process of oxidation.

When the hydroperoxides break down, they negatively affect the flavour and decreases the oil quality. Thermal (heat) oxidation increases lipid peroxidation and causes chemical changes in cooking oil.

Oxidation releases foul odours and affects flavour, nutritional values and health benefits. It is essential to refill the pan with oil before a frying shift; you do not want more oil sitting in your pan unused.

Topping up your pans with oil by a minimum of 1/3 a day will mean oxidation will be under control.

Many would say to limit exposure to air by covering the fryer when not in use; you cannot remove oxygen from the pan this way. However, it would be a good idea to use lids to reduce foreign bodies falling into your pan.

Seven enemies of Frying oil, Fish and chip shop, carbon

Carbon build-up from food particles is also one of the top prohibitors of oil longevity. Food pieces are likely to break down and fall to the bottom of the fryer. If you continue using the same oil to fry various batches of food, then they will transfer different flavours and aromas. When the carbon burns, it causes rancidity. The excess coating in fried foods can also cause foaming on the surface.

The best preventative measure (and one of the easiest) is to sieve the oil of crumbs after every batch of frying. While frequent frying will cause the oil to eventually breakdown, regular filtering will extend its shelf life. Another measure that you can take to keep your oil fresh is to use quality oils with a higher smoke point. The oil you fry with should be suitable for frying. 

Where regular filtering removes carbon from the frying oil, a regular boil-out removes carbon from the frying vessel. It is essential that you have a regular boil-out routine as it removes carbon, polymerised fats and keeps your probes working efficiently.

Tips to reduce carbon formation:

➡️ If you have one, use the snack pan on your range for breaded fried products. If you don’t have one, a countertop fryer or a separate commercial fryer is recommended. Breaded foods produce so much more carbon; this will move the issue away from your main fryers.

➡️ Use your snack pan, a countertop fryer or a separate commercial fryer for your meat products too. Sausages, burgers and chicken all release fat and water, which will breakdown your oil faster and also polymerise in the fryer.

➡️ Avoid floured products like fish without batter or southern fried chicken; the flour burns quickly and turns to carbon making your oil rancid.

➡️ If you have no intention of serving batter bits, then lift them out of the fryer as fast as you can as this will prevent them from burning and turning to carbon.

Seven enemies of Frying oil, Fish and chip shop, salt

During the frying process, salt acts as a catalyst and accelerates oxidation. This causes the oil to become darker in colour and release off-flavours, which affects the taste of the food. Salted products also release water and cause foam formation that can cause oil breakdown. Salt can also act as an impurity and lower the smoke point, which in turn degrades oil and shortens its life.

To prevent oil degradation, it is ideal to avoid adding salt before frying.

Make sure you fry to the crisp level you want, and don’t try to refry foods after adding salt. 

Want to season food before frying? Consider using Ceres Seasoned Rice Flour as it encapsulates the seasoning under the batter coating to reduce the impact on the frying medium.

Seven enemies of Frying oil, Fish and chip shop, water

We all know from chemistry that water and oil do not mix. During the frying process, heat causes food to release moisture and result in oil decomposition. Since foods absorb the oil, its degradation has adverse effects on the final properties that the food will have, including the nutrition and shelf life.

With frequent usage, eventually your oil will breakdown. When steam escapes during frying, it causes foaming and affects the flavour and the quality of your food. You can easily remedy the situation by following best practice: avoid overcrowding the pan, make sure fish is not wet before frying, and don’t fry at too low a temperature.

Reducing the amount of moisture entering the fryer is imperative. Here are some tips to help:

➡️ Ensure fresh chips are dry before frying.

➡️ Shake off frozen chips as this will remove/reduce ice crystals.

➡️ Consider using Ceres Super Absorbent Cloths to dry off your fish before frying.

➡️ If you have no intention of serving batter bits, then lift them out of the fryer as fast as you can as this will remove extra moisture from the fryer and help maintain your oil temperature.

Seven enemies of Frying oil, Fish and chip shop, light

Store liquid oil away from direct sunlight. Light accelerates chemical reactions, including degradation of oil.

When the fat molecules break down they cause the oil to go rancid. Some specific oils, such as rapeseed oil, have unique chemical structures that make them more vulnerable to going rancid and exuding an off smell.

The trick to increasing the longevity of your frying oil is to avoid those stored in clear containers. If your favourite oil always comes in a transparent bottle then store in a cool, dark place and keep the caps tight.

Seven enemies of Frying oil, Fish and chip shop, heat

Extreme temperatures break down frying oil faster and, in most cases, even when your food is crispy on the outside, it tends to be overcooked on the inside.

The solution for preventing breakdown caused by heat is to keep your cooking oil at its ideal frying temperature by regularly checking pan temperatures. Any fluctuation from the display temperature will give you inconsistently fried food.

Don’t be tempted to fry at too low a temperature; this will result in unevenly fried food with higher moisture content in the food and the frying oil.

When not busy, switch off any idle fryers or set the temperature to 100°C.

Seven enemies of Frying oil, Fish and chip shop, soap

Cleaning compounds and degreasers tend to be alkaline, and soaps are surfactants, which means they can react with oil and water. They have elements that are both hydrophilic (water-loving) and lipophilic (fat-loving).

Tiny amounts of soap can break down frying oil and result in the degradation compounds that compromise food flavour, aroma and overall life.

The goal is to keep alkaline materials out of your fryer. There is not much you can do with foods and food ingredients.

When cleaning down the frying range, scrape off dry deposits and use mild-warm water, Ceres Deep Fryer Cleaner solution and a microfibre or super-absorbent cloth to remove dirt. Don’t lather the frying range, just clean a small area at a time, repeating the process and wringing out the cloth to remove any excess solution.

An often overlooked cause is cooking utensils. Dish soap and degreasers are alkaline and stick to the surface when dried, so rinse all cooking utensils that have been washed with soaps and make sure they are dried thoroughly before use.


In this guide, we have covered the main issues that concern frying oil degradation.

It is also worth making sure you use stainless steel utensils as trace metals (copper, iron, brass) will break down your frying medium faster. And regularly check the condition of your pans as pitted pans will expose raw metal, further contributing to oil breakdown.

Oil management is critical; you should have a routine of filtering at least twice a day and topping up your oils. If you do not top up with a sufficient amount of oil, you will find that the oil will spoil faster. As a rule of thumb, you want to top up oils by 30%, but take your time to get the balance right. If your oil levels are too low in the fryer, you run the risk of burning oil faster and having unevenly fried food. If your oil levels are too high, your fryers will not recover quickly enough and you will not be able to top up sufficiently.

We cannot stress how vital regular oil filtration is. This will increase oil life and quality, and food quality. As crucial as filtering is, without a clean fryer, your oil will also breakdown faster than you would like, so we recommend a regular boil out to keep on top of carbon build up on the fryers.

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