How Peanut Oil Is Made: From Groundnuts to Cooking Oil

Peanut oil is made by drying and shelling groundnuts, crushing the kernels, then pressing them (and sometimes using a solvent) to release the oil. The oil is filtered to remove solid particles. It is then either bottled as it is, as cold-pressed or roasted peanut oil, or refined into a pale, neutral oil. Refined peanut oil is the clear, golden liquid many cooks use for high-heat stir-frying and deep-frying, including Thai dishes cooked in a wok. This article walks through the peanut oil production process step by step. It also explains how to recognize each type of peanut oil by color, aroma and texture, and what each one brings to Thai food.

What is peanut oil, and is it the same as groundnut oil?

Peanut oil and groundnut oil are the same product: a vegetable oil pressed from the seeds of the peanut plant. "Groundnut" is simply another name for the peanut, because the pods ripen underground. This is why you will see "groundnut oil production" and "peanut oil production" used for the same process.

Peanut kernels are naturally rich in fat. Roughly half of a shelled kernel's weight is oil, which is why peanuts have long been an important oil crop. Squeeze a freshly roasted peanut between your fingers and you can feel that oiliness on your skin.

In a Thai kitchen, peanuts usually appear as whole or crushed roasted nuts. Think of the crunchy topping on pad thai, the thick sauce served with satay, or the soft peanuts simmered in massaman curry. Peanut oil is a separate ingredient. It is the cooking fat that carries heat and flavor, rather than a flavor you notice on its own.

How is peanut oil made? The peanut oil production process step by step

The peanut oil production process moves through seven main stages: harvesting and drying, shelling and cleaning, conditioning, pressing, optional solvent extraction, filtration, and optional refining. Small mills may stop after filtration. Large industrial plants usually carry the oil through full refining.

1. Harvest and dry the groundnuts. Farmers lift the plants from the soil and leave the pods to dry. Drying lowers the moisture content, which helps prevent mold and spoilage in storage.
2. Clean and shell. Machines remove soil, stones, stems and other debris. Shelling machines, called decorticators, then crack the papery-brown pods. The shells are separated from the pinkish-red, skin-covered kernels.
3. Sort and condition. Damaged or moldy kernels are removed. The good kernels are then often heated, and sometimes roasted, to adjust their moisture and soften them so the oil flows more easily. Heavier roasting produces a darker oil with a stronger nutty smell.
4. Crush or flake. The kernels are broken into coarse pieces or flattened into flakes. This exposes more surface area and opens up the cells that hold the oil.
5. Press. A screw press, also called an expeller, pushes the crushed kernels through a narrowing barrel under high pressure. Golden oil seeps out through small gaps. A dry, compact "press cake" is pushed out of the other end.
6. Extract the remaining oil with a solvent (industrial plants only). Pressing leaves some oil behind in the cake. Large mills may wash the cake with a food-grade solvent, commonly hexane, to dissolve the remaining oil. The solvent is then evaporated off and recovered. The oil-poor cake that remains is typically used as animal feed.
7. Settle and filter. Freshly pressed oil is cloudy with fine particles. It is left to settle and then passed through filters until it runs clearer.
8. Refine (for refined peanut oil). The filtered crude oil goes through a series of cleaning steps that make it pale, mild in smell and stable at high temperatures. These steps are described below.

What happens during pressing?

Pressing is the mechanical oil extraction step that physically squeezes oil out of the crushed peanuts. No chemicals are involved in pressing itself.

"Cold-pressed" peanut oil is pressed with minimal added heat, so more of the original peanut flavor and color is kept. Expeller pressing at higher temperatures yields more oil. The trade-off is that friction and heat can change the oil's flavor.

Why is filtration needed?

Filtration removes tiny bits of peanut solids and moisture that would otherwise make the oil cloudy and cause it to spoil faster. Unfiltered or lightly filtered peanut oil can look hazy and leave a sediment at the bottom of the bottle. Well-filtered oil looks clear when you hold it up to the light.

What does refining involve?

Refining is a series of treatments that turns crude peanut oil into a clear, light-colored oil with very little smell or taste. The main stages are:

• Degumming: removes gummy substances, mainly phospholipids, usually by treating the oil with water or a mild acid.
• Neutralizing: removes free fatty acids, which can cause off-flavors and smoking at lower temperatures.
• Bleaching: passes the oil through absorbent clays that pull out color pigments, leaving a pale yellow oil.
• Deodorizing: heats the oil with steam under vacuum to strip away strong-smelling compounds, including much of the peanut aroma.

The result is an oil that tastes almost neutral and tolerates high heat well. These are exactly the qualities that suit fast wok cooking and deep-frying.

How do cold-pressed, roasted and refined peanut oil differ?

The three common types of peanut oil differ mainly in how much processing they receive, and that changes their color, aroma and best use.

Type	How it is made	Color and look	Aroma and taste	Best use in Thai-style cooking
Refined peanut oil	Pressed and/or solvent-extracted, filtered, then degummed, neutralized, bleached and deodorized	Pale yellow, very clear	Mild, almost neutral	Stir-frying in a wok, deep-frying fish cakes, crispy omelettes and spring rolls
Cold-pressed (unrefined) peanut oil	Pressed with little added heat, then filtered only	Golden to amber, sometimes slightly hazy	Clearly nutty, like fresh peanuts	Gentle sautéing and dressings where a peanut note is welcome
Roasted (toasted) peanut oil	Pressed from roasted kernels, filtered only	Deep amber	Strong roasted-peanut aroma	A few drops to finish a dish, or a peanut-sauce accent; not for high-heat frying

Smoke point is the temperature at which oil begins to smoke and break down. Refined peanut oil is widely regarded as having a high smoke point. Unrefined and roasted peanut oils smoke at noticeably lower temperatures, so they are better for gentle cooking or finishing than for blasting a wok over high heat.

How can you recognize peanut oil in the bottle and in the pan?

You can recognize peanut oil by its color, its smell when warmed, and the light, smooth way it moves in the pan.

• Color: Refined peanut oil is pale straw-yellow and transparent. Cold-pressed oil is a richer gold. Roasted oil is amber, similar in shade to light honey.
• Aroma: Warm a spoonful. Refined oil smells faint and clean. Unrefined oil gives off a soft scent of shelled peanuts. Roasted oil smells like a freshly opened bag of roasted nuts.
• Texture: Peanut oil feels smooth and fairly light on the fingertips, not sticky. In a hot wok it spreads quickly into a thin, shimmering film.
• In the fridge: Peanut oil can turn cloudy and partly thicken when chilled. This is normal, and it clears again at room temperature.

Spoiled oil: Rancid peanut oil smells stale, bitter or like old paint or crayons. If you notice that smell, replace the oil, because it will pass the flavor straight into the food.

How is peanut oil used in Thai cooking?

In Thai-style cooking, refined peanut oil is used mainly as a high-heat frying fat that lets garlic, chilies and herbs sizzle quickly without adding a heavy flavor of its own. Thai home cooks also commonly use other oils, such as palm, soybean or rice bran oil. Peanut oil is valued for similar reasons: it handles heat well and stays out of the way of bold seasonings.

Stir-frying in a wok

A Thai wok is a wide, round-bottomed pan. Its shape lets a small amount of oil pool in the hot center while food is tossed up the sloping sides.

For a dish like pad krapow (stir-fried holy basil with minced meat), the steps are simple:

1. Heat a few tablespoons of refined peanut oil until it shimmers.
2. Add pounded garlic and chilies for a few seconds, until fragrant and just turning golden.
3. Add the meat and sauces.
4. Stir in the basil at the end.

The neutral oil lets the sharp, peppery smell of holy basil and the salty-sweet sauces lead.

Deep-frying

Deep-fried Thai favorites include:

• Tod man pla: springy red-curry fish cakes.
• Kai jeow: a puffy, lacy-edged Thai omelette poured into very hot oil so it balloons and turns golden-brown.
• Crispy spring rolls.

A wire-mesh spider strainer is the usual tool for lifting food out of the oil and letting it drain.

A simple readiness test needs no thermometer. Dip the tip of a dry wooden chopstick into the oil. If steady small bubbles rise around it, the oil is ready for frying.

Crispy garlic and shallot oil

Thai cooks often slowly fry thin slices of garlic or shallots in oil until they turn light gold and crisp. Both parts are useful:

• The crispy slices are scattered over noodle soups, rice porridge and salads.
• The fragrant oil left behind is drizzled over finished dishes.

A neutral refined peanut oil works well here because it picks up the garlic or shallot aroma cleanly. Remove the slices just before they look done, because they keep darkening and can turn bitter within seconds.

Peanut oil versus peanut ingredients

Refined peanut oil does not make food taste of peanuts. The roasted, nutty flavor in satay sauce, pad thai or massaman curry comes from the peanuts themselves, which are usually roasted and crushed in a mortar and pestle. If you want a stronger peanut note, a little cold-pressed or roasted peanut oil can add it. It cannot replace the texture and body of real crushed peanuts.

What can you use instead of peanut oil?

Any neutral oil that tolerates high heat can stand in for refined peanut oil in most Thai stir-fries and deep-frying. Each substitute has its own limitations:

• Rice bran oil: mild and good for high heat; a close everyday swap.
• Soybean or canola (rapeseed) oil: neutral and widely available; fine for stir-frying. Very old or reused soybean oil can develop a fishy or painty smell.
• Palm oil: handles frying well and is common in Thailand. It can feel slightly heavier and may thicken or turn cloudy in cool rooms.
• Sunflower oil: neutral and light. Standard types are less stable at high heat than high-oleic versions.
• Olive oil: not a good match. Its fruity or grassy flavor clashes with Thai aromatics, and extra-virgin olive oil is less suited to very high wok heat.

Is peanut oil safe for people with peanut allergies, and how should it be stored?

Allergies: Highly refined peanut oil has most of its proteins removed during refining. Cold-pressed, expeller-pressed and roasted peanut oils can still contain peanut proteins, which are what trigger allergic reactions. Anyone with a peanut allergy, or cooking for someone who has one, should check the label and follow their doctor's advice rather than assume any peanut oil is safe. When cooking for guests, it is courteous to mention that a dish was fried in peanut oil.

Storage: Keep peanut oil in a tightly closed bottle in a cool, dark cupboard, away from the heat of the stove. Unrefined and roasted peanut oils go stale faster than refined oil, so buy them in smaller bottles and use them more quickly.

Reusing frying oil: If you reuse frying oil, strain it through a fine sieve or cloth once it has cooled. Discard it when it darkens heavily, smells off or starts to foam.