What Is Seasoning and Why Does Oil Choice Matter?

Imagine the kitchen of a farmhouse in the Yorkshire Dales in the 1890s. The cook there did not own a bottle of high-oleic sunflower oil, nor a jar of refined coconut oil ordered from a health food website. She used lard — the rendered fat skimmed from her own pigs — and her cast iron skillet was as black as coal and virtually frictionless. She seasoned by instinct, cooking fatty foods again and again until the pan built up its own protective layer over years of use.

Today, most of us are starting from scratch with a new pan or restoring a rusty one. We need to apply seasoning deliberately, and that means choosing an oil wisely. The oil you choose determines:

• How well the seasoning bonds to the iron
• Whether the surface becomes smooth and hard or sticky and soft
• How quickly the seasoning builds up over multiple rounds
• Whether the pan develops off-flavours that affect your cooking
• How safe the process is at high oven temperatures

In the United Kingdom, where oven temperatures are often given in both Celsius and gas mark, and where many home ovens top out at around 230–250°C, the smoke point of your chosen oil is a critical factor that British cooks must understand before they begin.

The Science Behind a Good Seasoning Oil

Polymerisation: What Actually Happens

When you apply a very thin layer of oil to cast iron and heat it above its smoke point, the fatty acids in the oil undergo a process called polymerisation. The individual fat molecules link together and then oxidise, forming a hard, plastic-like coating that is bonded to the pan’s porous iron surface. This is the seasoning layer.

The key word here is thin. Many first-time cast iron owners make the mistake of applying oil generously, as though buttering toast. The result is a thick, sticky layer that never fully polymerises — it just sits there, gummy and unpleasant. A truly effective seasoning coat is barely visible. You should apply the oil and then wipe almost all of it back off before it goes into the oven.

Iodine Value and Why It Matters

Not all fats polymerise equally well. The key chemical property to look for is a high iodine value, which indicates a high proportion of polyunsaturated fatty acids. Oils rich in polyunsaturated fats polymerise more readily and form harder, more durable seasoning layers. This is why some oils — such as flaxseed oil — have become popular choices in cast iron communities despite being expensive and unusual cooking fats.

Monounsaturated fats (found in olive oil and most vegetable oils) polymerise more slowly and less completely. Saturated fats (found in lard, coconut oil, and butter) polymerise poorly for seasoning purposes but are excellent for cooking in a well-seasoned pan.

Smoke Point Considerations for UK Ovens

To polymerise properly, you need to bake the pan at a temperature above the oil’s smoke point. Most UK home ovens reach a maximum of 230–260°C (450–500°F), or around gas mark 9. You need an oil whose smoke point falls within a usable range — high enough that you can reach and exceed it without specialised equipment, but not so high that your oven cannot reach it at all.

Unrefined oils generally have lower smoke points than refined versions of the same oil. For seasoning purposes, refined oils are usually preferable.

The Best Oils for Seasoning Cast Iron in the UK

1. Flaxseed Oil (Linseed Oil) — The Enthusiast’s Choice

Ask on any British cast iron forum — and there are several active ones — and someone will invariably mention flaxseed oil. Food-grade flaxseed oil has one of the highest iodine values of any culinary fat, which means it polymerises aggressively and forms an exceptionally hard, glossy seasoning layer in relatively few applications.

In the United Kingdom, flaxseed oil is available from health food shops such as Holland & Barrett, from online retailers, and increasingly from larger Tesco and Sainsbury’s stores, often shelved alongside supplements rather than cooking oils. Make sure you purchase food-grade oil, not the industrial linseed oil sold at DIY shops — the latter contains additives and solvents that are entirely unsuitable for cookware.

Pros: Extremely hard finish, fast build-up, excellent durability once cured

Cons: Expensive, short shelf life (goes rancid quickly), unforgiving if applied too thickly — flaking can occur

Smoke point (refined): Approximately 107°C — very low, which is exactly the point. You must exceed it substantially.

Best used for: Initial seasoning of a new or stripped pan, restoration projects

2. Rapeseed Oil — The British Cook’s Practical Choice

Rapeseed oil is the unsung hero of British cast iron seasoning. Those bright yellow fields you see rolling across East Anglia and Yorkshire in early summer are almost certainly oilseed rape, much of which ends up pressed into the cold-pressed or refined rapeseed oil sold in every supermarket across the country.

British-grown, refined rapeseed oil has a high smoke point of around 200–232°C (depending on the refining process), a reasonably high proportion of polyunsaturated fats, and a mild, neutral flavour. It is also relatively affordable — a bottle of standard refined rapeseed oil from Aldi, Lidl, Morrison’s, or Asda costs very little and lasts a long time when used for seasoning, since you only ever apply extremely thin coats.

Cold-pressed rapeseed oil — the dark golden variety from producers like Borderfields or Farrington’s Mellow Yellow — has a lower smoke point and stronger flavour, making it less suitable for seasoning but delicious for cooking once your pan is well-seasoned.

Pros: Widely available throughout the UK, inexpensive, good polymerisation, genuinely British-grown option

Cons: Slightly lower iodine value than flaxseed oil; builds up more slowly

Smoke point (refined): Approximately 200–232°C

Best used for: All-round seasoning and maintenance, particularly good for ongoing care after cooking

3. Sunflower Oil — The Household Staple

High-oleic sunflower oil is one of the most commonly recommended seasoning oils in British cast iron circles, largely because almost every household in the UK already has a bottle in the cupboard. Standard refined sunflower oil has a smoke point of around 225–230°C and contains a reasonable proportion of polyunsaturated fats.

It is worth noting that the term “high-oleic” refers to a specific variety of sunflower oil with more monounsaturated fat (oleic acid) and less polyunsaturated fat. Confusingly, some cast iron enthusiasts prefer high-oleic versions for their stability, while others prefer standard sunflower oil for its higher polyunsaturation. For most UK home cooks, the distinction matters less than the technique — standard refined sunflower oil from any UK supermarket will season a pan perfectly well.

Pros: Found in virtually every UK kitchen, cheap, reliable, neutral taste

Cons: Not as fast-building as flaxseed oil; moderate iodine value

Smoke point (refined): Approximately 225–230°C

Best used for: Regular maintenance seasoning, topping up between cooks

4. Crisco / Vegetable Shortening — American-Influenced but Available in the UK

American cast iron culture, which is heavily influenced by brands like Lodge and online communities on Reddit’s r/castiron, frequently recommends Crisco vegetable shortening. While Crisco itself is not widely sold in UK supermarkets, equivalent vegetable shortenings are available — Trex is the most common British equivalent, found at Tesco, Waitrose, and most supermarkets, and widely used in British baking for pastry and biscuits.

Vegetable shortening contains a blend of fats, often partially hydrogenated, with a moderate smoke point. It is easy to apply, coats evenly, and produces a reliable if unremarkable seasoning layer. Lodge, the American cast iron brand sold extensively in the UK through retailers like Amazon UK, Lakeland, and John Lewis, ships its pans pre-seasoned with 100% vegetable oil.

Moving Forward

Once you have the fundamentals in place, the possibilities open up considerably. The UK offers fantastic opportunities for anyone interested in this hobby, and with the right foundation you will be well placed to make the most of them.