Home: Re-using of Frying Oil

Vegetable oil has proven itself to be the substance of choice for deep frying food in the UK. The question often arises of how long you can keep using the oil.

From a safety standpoint, it's fairly safe to continue using oil for more than one batch of food. But some researches have suggested it becomes an increasing fire risk as it is reused.

They have noted four of five stages of degradation. Interestingly, it has been noted that oil may need to be fried once or twice until it is at it's optimum performance. But, after that it will lower from optimal, to fresh, to degraded, to rancid, and then to a lowering of it's smoking point.

The lowering of the smoking point is the real risk. At this point the oil can more easily catch fire, and due to it's unstable condition, you can not know a safe temperature to fry at, as the smoking point is unknown and therefore unreliable.

Putting a date to this degradation is impossible. One household may fry with their oil 6 times a day, and another once a week. But, it is wise to bear in mind the degradation cycle in oil, from a fire risk standpoint.

The re-use of frying oil does pose some further issues however,

1. To health

2. To the quality of the food produced

From a health standpoint, it is fairly obvious to anyone who deep fries, that a residue of the food previously cooked is left in the oil. Not only can you see the little bits of batter etc floating in the oil, there is also the unseen fat left by the previous fried batches.

These fats can include trans fats and HME compounds which are believed to increase the risk of heart disease.

As stated, the quality of the oil degrades after each use, and especially if the oil has been overheated. This will result in worse and worse cooking results. Which will probably be the best gage you have for indicating the time to replace your oil. The colour of the oil may darken as well.

Disposing of re-used oil is fairly straight forward. Place it in a container and throw it into the rubbish bin. Do not dispose of it down the drain. And of course, some people are even re-using frying oil to power their diesel cars.