Temperature
Setting the correct temperature on your deep fat fryer is paramount to cooking the food correctly. If the temperature is too low then the food will absorb too much of the oil making it greasy and if it's too high then it will overcook on the outside and potentially undercook on the inside!
If your food browns too quickly and hasn't had enough time to cook properly on the inside, don't worry as what you can do is remove it from the deep fat fryer and place in the oven at 190°C for around 5-10 minutes until the inside has been cooked.
Wet Food
Wet food should never be put in your deep fat fryer. Always ensure food is dry - pat with a tea towel or kitchen roll to dry anything wet (such as chips/fries) before putting in a fryer.
Overcrowding
Do not overcrowd your deep fat fryer as not only can it cause uneven cooking, but putting too much in to your fryer can lower the temperature of the oil leading to potentially greasy and undercooked food.
What Oil Should You Use?
Rapeseed oil, sunflower oil, peanut oil or avocado oil all have high smoke points which makes them suitable for deep fat frying.
Which Is the Healthiest?
Generally speaking, rapeseed oil (AKA canola oil) is the 'healthiest' of the oils mentioned above. It has a lower saturated fat than sunflower oil for example and higher Omega-3 and Monounsaturated fats too. Overall there is a better mix of fats in rapeseed oil.
How Many Times Can You Reuse Rapeseed Oil When Deep Fat Frying?
The answer to this question is that it depends on what you are cooking!
Each time the oil is heated up to temperature the smoke point (literally the temperature when the oil starts smoking) lowers, so the more you reuse the oil the lower the smoke point becomes making it less safe to use and the flavour of the oil also changes.
| Oil Type | Approx. Smoke Point | Best Use |
|---|---|---|
| Rapeseed (Canola) | 200–220°C | Deep frying, roasting |
| Sunflower | 225°C | High-heat frying |
| Olive (Extra Virgin) | 160–190°C | Low-heat sautéing, dressings |
| Peanut | 230°C | Stir-frying, deep frying |
| Butter | ~150°C | Gentle cooking, sauces |
The oil breaks down faster when frying battered and breaded foods so you can safely use the oil 2-4 times before the smoke point is too low. For non-breaded foods (such as chips/fries) you should be able to get 6-8 uses out of it.
You should always filter the oil before re-using it. Some deep fat fryers have built in filtering systems that you can use after the oil has cooled down.
| Factor | Breaded foods | Non-breaded foods | Best practice |
|---|---|---|---|
| Typical safe reuses | 2–4 times | 6–8 times | Filter after each use; store properly |
| Storage life | Up to 3 weeks | Up to 3 weeks | Keep sealed; refrigerate for quality |
| Warning signs to discard | Dark color, thick texture, foaming | Off smell, bitter taste, excess smoke | Replace oil when any sign appears |
Some people/websites may say you can store used oil for up to 3 months, in reality this is ill advised as even if it hasn’t gone rancid, reused oil degrades chemically with each heating cycle. By the time you’ve fried in it several times, its flavour, smoke point, and nutritional quality are compromised. That’s why professional kitchens rarely keep used oil beyond a few days and for home cooking filtered used oil is be discarded within 2-3 weeks.
3-Step Home Test for Used Frying Oil
1. Visual Check
- Look for cloudiness or separation – Good oil should be clear and uniform.
- Check for darkening – If the oil has turned amber or brown, it’s likely degraded.
- Watch for thickening – If it pours slowly or feels sticky, it’s polymerised and should be discarded.
2. Smell Test
- Fresh oil smells neutral or slightly nutty.
- Bad oil smells sour, fishy, metallic, or like old paint — that’s rancidity.
- If it makes you wrinkle your nose, it’s time to bin it.
3. Foam Test (Quick Fry Trial)
- Heat a small amount of the oil in your fryer or pan to normal frying temperature (around 180 °C).
- Drop in a small piece of bread or potato.
- Watch for excessive foaming or smoking — that’s a sign the oil has broken down.
- If the food browns too fast or tastes bitter, the oil’s done.
🛑 When to Discard Immediately
- Foams aggressively at normal heat
- Smells off even when cold
- Leaves a sticky residue on pans or food
- Makes fried food taste stale, greasy, or burnt
This test is quick, low-effort, and gives you a solid sense of whether your oil is still safe and tasty. If you’re ever unsure, err on the side of caution — fresh oil makes a world of difference in flavour and texture.
Does Reusing Oil Increase Your Risk Of Cancer?
| Risk Compound | How It Forms | Cancer Link | Mitigation |
|---|---|---|---|
| Acrylamide | High-temp frying of starches | Probable carcinogen | Fry at ≤180°C, avoid over-browning |
| PAHs | Overheated oil, charred food | Known carcinogens | Avoid burning, discard degraded oil |
| HCAs | Frying/grilling meats | Possible carcinogens | Cook at moderate heat, avoid charring |
| Aldehydes | Repeated oil reuse | Linked to oxidative stress | Limit oil reuse, filter regularly |