Which Frying Oil to Use and When to Replace It

Smoke point, and why it matters more with use

The smoke point is where an oil starts to break down visibly. Past it the oil develops acrid flavours, produces more free radicals and polar compounds, and is closer than you want to its flash point.

Frying happens at 160 to 190 °C, so you want something comfortably above.

Smoke point falls with use. Every session introduces food particles and water, both of which accelerate breakdown, and each cycle of heating produces free fatty acids that lower the smoke point further. Oil that starts smoking at a temperature it handled fine last month has degraded and should go.

Which oil for which job

Chips. Peanut or groundnut oil, if you can. It has a genuine nutty note that is part of why Five Guys chips taste the way they do, and the company says so on the wall. Beef dripping gives an excellent and entirely different British chip-shop result.

Fried chicken. Anything neutral with a high smoke point. Rapeseed or vegetable oil. The seasoning is doing the flavour work and an oil with character fights it.

Doughnuts and sweet frying. Neutral, and keep it separate from savoury oil afterwards - it picks up sugar and vanilla and will flavour the next batch of chips.

Shallow frying and pan work. Whatever you have. The volumes are small enough that cost and reuse matter much less.

What to avoid across the board: extra virgin olive oil, which smokes below frying temperature and is a waste of an expensive ingredient; butter, whose milk solids burn at 150 °C; and any unrefined or cold-pressed oil, which has a much lower smoke point than its refined equivalent.

On nut allergies: if peanut oil is out, refined rapeseed plus a tablespoon of toasted sesame oil per litre stirred in after cooling gets you a comparable nutty top note. It is not the same and the recipes say so.

How many times you can reuse it

Reusing frying oil is normal and economical. The limits depend entirely on what you fried.

• Chips and vegetables: 4 to 6 sessions. Little protein, little debris.
• Coated chicken: 2 to 3. Batter fragments burn and accelerate breakdown.
• Fish: once. The flavour transfers to everything afterwards.
• Sweet frying: 2 to 3, and never afterwards for savoury.

Strain it warm, not hot - through a fine sieve lined with muslin or a coffee filter, into a clean sealed container, stored somewhere dark and cool. Light and air are what degrade it between uses.

The five signs it should go, any one of which is enough:

1. It has darkened noticeably.
2. It smells rancid, fishy or like old chips.
3. It foams across the whole surface rather than bubbling around the food.
4. It smokes below its normal working temperature.
5. It has become syrupy or sticky when cold.

Foaming is the most reliable one. It means the oil has polymerised enough to hold bubbles, which is a fairly late stage of degradation.

Disposal, and why it matters

Never pour cooking oil down a sink or a drain.

Oil cools and solidifies in pipes, and combines with wet wipes and other solids to form the fatbergs that block municipal sewers. UK water companies spend tens of millions a year clearing them, and a domestic pipe blocked with congealed fat is an expensive plumbing bill.

What to do:

1. Let it cool completely in the pan. Never move hot oil.
2. Pour it into a sealed container - the bottle it came in, a milk carton, a jar.
3. General waste, or better, a recycling point. Many local authority tips and some supermarkets accept used cooking oil, which is processed into biodiesel.

Small quantities - a tablespoon or two from a pan - can be wiped out with kitchen paper and binned.

Never put it in food waste collections or compost, where it attracts vermin and interferes with the composting process.