How it's made

Steam distillation vs cold pressing: why one oil is distilled and the other pressed

Steam distillation and cold pressing are not two grades of the same craft — they are two different tools that recover two chemically different kinds of oil, and neither can do the other's job. Oregano oil can only be distilled. Black seed oil can only be pressed. Once you know why, a great deal of what gets written about extraction methods stops being a quality debate and starts being a straightforward question of which molecule you are trying to move.

Which method is better, steam distillation or cold pressing?

Neither, because they are not alternatives for the same job — and almost every article that ranks them against each other is answering a question that does not exist. The two methods separate oils by completely different physical properties. Steam distillation selects by volatility: it moves molecules that are willing to travel as a vapour. Cold pressing selects by mechanical release: it squeezes a liquid that was already sitting in the seed as a liquid. A plant material that holds a volatile oil cannot be usefully pressed, and a seed oil that will not evaporate cannot be distilled at all.

So the honest framing is this: the method is chosen by the chemistry of the target compound, not by a manufacturer's commitment to quality. Where a genuine quality question does exist — and it does — it sits within each method, in how carefully it was run, rather than between them.

What is the actual difference between a volatile oil and a fixed oil?

A volatile oil evaporates and a fixed oil does not, and you can demonstrate the difference on a sheet of paper in an afternoon. Put a drop of an essential oil on paper and come back later: it will have largely gone, leaving little or no permanent mark, because its constituent molecules are small and have appreciable vapour pressure at room temperature. Put a drop of a pressed seed oil on the same paper and the translucent stain is still there next week, because triglycerides — the fat molecules that make up the bulk of a seed oil — are large, heavy and have essentially no vapour pressure. Heat them enough to move and they decompose rather than evaporate.

This single property decides everything downstream. It decides which extraction method is even possible. It decides how each oil ages — a volatile oil loses potency partly by literally leaving the bottle, while a fixed oil goes rancid by oxidising in place, which is why the two run on two different expiry clocks. And it decides how the two behave in a glass of water: the volatile aromatic compounds are what you smell, and the fixed oil is what carries them.

Why can carvacrol be distilled at under 100 °C when it boils at 237 °C?

Because when two liquids that do not mix are boiled together, their vapour pressures add rather than average — so the mixture boils below the boiling point of either one. This is the mechanism at the heart of steam distillation and it is almost never stated in consumer articles about extraction, which is a pity, because it is the whole reason the technique is worth using.

Work the numbers. Carvacrol, the principal phenolic constituent of oregano oil, is reported to boil at roughly 236–238 °C at atmospheric pressure. Water boils at 100 °C. Oil and water do not mix, so in a still their separate vapour pressures sum, and the combined mixture reaches atmospheric pressure — and boils — at a temperature slightly below water's own 100 °C. Carvacrol therefore leaves the plant material about 140 °C below the temperature at which it would boil on its own. That is the point of the whole apparatus: steam distillation is the standard technique for a compound that boils above water and would decompose long before reaching its own boiling point. The steam is not there to cook the plant. It is there to lower the temperature at which the target will travel.

One consequence worth knowing as a buyer: different constituents come over at different rates, with the lighter molecules distilling off early and the heavier ones such as carvacrol arriving later. Distillation time is therefore not a neutral setting — a run cut short and a run taken to completion produce oils of measurably different composition from the same plant. This is one of the quiet variables behind why two bottles of honestly-made oregano oil can differ, and part of why the carvacrol percentage is worth reading rather than assuming.

Why is black seed oil cold-pressed instead of distilled?

Because the oil in a black seed is a fixed oil that cannot be distilled, and because its most-discussed constituent does not tolerate the temperatures a still runs at. Nigella sativa seeds store oil the way most oilseeds do — as triglycerides held in the seed tissue, ready to be released by crushing. There is nothing to vaporise. Run a still on black seed and you would recover a small volatile aromatic fraction and leave the actual oil behind.

The second reason is thermal. Thymoquinone, the constituent black seed oil is characterised on, is repeatedly described as heat-sensitive, with degradation reported in the region of 80–100 °C. Cold pressing exists precisely to stay far below that: the seed is crushed mechanically with no added heat and no solvent. And there is a genuine trade-off buried here that trade sources are candid about — expeller pressing, which uses a screw press generating friction heat, is commonly quoted at higher yields than a cooled cold press, sometimes reported in the region of 35–45% against 25–35%. The method that extracts more oil from the seed does so by letting the seed cake get warmer. Choosing the lower-yielding method is a deliberate decision to trade volume for the integrity of a heat-sensitive constituent, and it is one of the few places in this category where a process claim maps onto a real, costly choice.

How cold is "cold-pressed", and is the term regulated?

Cold-pressed means mechanically pressed with no added heat and no solvent, with reported process ceilings clustering around 40–49 °C (roughly 104–120 °F) — but there is no US federal definition of the term for a dietary supplement, so it is a description a company is offering rather than a certified specification. Different reference points circulate: some producers target below 40 °C specifically to protect heat-sensitive constituents; below 49 °C / 120 °F is the figure most commonly quoted for cold pressing generally; and in the one commodity where the EU does define a comparable term, cold extraction of olive oil, the ceiling is set considerably lower still.

It is worth being precise about what that does and does not mean, because it is easy to over-correct into cynicism. An undefined term is not automatically an empty one. "Cold-pressed" describes a real, physically meaningful process with a measurable temperature — a company stating it has said something that could in principle be checked, and something that carries a real cost in lost yield. That puts it in a different class from the ungraded grade words discussed on our page comparing oil of oregano and oregano essential oil, which describe nothing at all. The reasonable position is that a process claim is informative but unverified, and that it should be read alongside things that are verifiable — a stated milligram figure per serving, and independent testing.

How do the two methods compare, point by point?

They differ on nearly every axis except the goal of getting oil out of a plant without solvents. The table below sets them side by side on the properties that actually decide which one a producer can use.

General process characteristics compiled from published extraction literature and industry practice. Figures vary with species, plant part, equipment and run conditions; they describe the methods rather than any single bottle.

Why does pressing yield so much more oil than distilling?

Because a seed oil is bulk storage and an essential oil is a trace defensive fraction — and the size of that gap explains most of the price difference in the category. Published cold-press yields for Nigella sativa commonly land around 22–35% of the seed's weight, with the seed's total oil content often quoted at 25–40%. Roughly a third of a black seed is oil, and pressing is the business of getting it out. Oregano is the opposite case: published essential oil yields vary a great deal with subspecies, plant part, drying method and distillation time, but they typically sit somewhere between a fraction of a percent and a few percent of the dried plant, with the carvacrol-rich subspecies at the upper end.

Put the same 100 grams of raw material through each process and you get tens of grams of pressed seed oil against something on the order of a gram — sometimes much less — of distilled oregano oil. That is a difference of one to two orders of magnitude from the same weight of plant, and it has three practical consequences. It is why the distilled component of a blend is measured in milligrams per serving while the pressed component is the base those milligrams sit in. It is why a concentrated oregano oil needs a 2-drop serving rather than a teaspoon. And it is why dilution with a cheap filler is the characteristic adulteration in this category rather than an occasional lapse — when an ingredient is that scarce, there is a standing economic reason to stretch it, which is the context behind independent label testing mattering as much as it does.

Does distillation purify the oil in a way pressing does not?

It selects, which is not quite the same as purifies — but the selection is real and it is worth understanding. Only what can travel as a vapour comes over in the steam, so waxes, pigments, chlorophyll, resins and the heavy non-volatile material of the plant stay behind in the still by simple physics. Pressing has no equivalent filter: whatever is in the seed and is oil-soluble ends up in the oil. That is a structural difference between the two products, not a virtue of one company over another.

The honest qualification is that volatility is an indifferent gatekeeper — anything volatile carries over too, so distillation is not a purification guarantee and does not substitute for good raw material or independent testing. What it does mean, usefully, is that the two components of a blend should be judged on different evidence. For the distilled oil, ask about the plant: species, chemotype, wild or cultivated, and the resulting carvacrol content. For the pressed oil, ask about the seed: origin, freshness and how it was stored before pressing, because a pressed oil inherits the condition of its seed almost directly. Our page on wild versus cultivated oregano covers the first half of that in detail.

Where does supercritical CO₂ extraction fit in?

It is a third route that sits between the two, using neither heat nor mechanical force but carbon dioxide held at a pressure and temperature where it behaves as a solvent. It runs cool, which is its main attraction, and it carries over some heavier fat-soluble material that steam distillation leaves in the still — so a CO₂ extract of the same plant is not compositionally identical to a steam-distilled oil of it, even though both may be sold under the same name. As a buyer the point is not that one is superior but that the extraction method is part of the identity of what is in the bottle, and a label that names it has told you something a label that does not has withheld.

What does this mean when I am reading a label?

Check that the stated method matches the class of oil — it is a four-second test, and a mismatch is a genuine signal. "Cold-pressed oregano oil" should stop you: you cannot press an essential oil out of a leaf. A product described that way is either an infusion — oregano steeped in a carrier oil, which is a legitimate but far weaker product and a different thing entirely — or loose copywriting on a bottle whose other claims then deserve the same scepticism. The mismatch runs the other way too: "steam-distilled black seed oil" would describe a volatile aromatic fraction, not the fixed oil that black seed oil means to almost everyone buying it.

Three things follow. Expect a combination product to name two different methods, because a genuine blend of a distilled oil and a pressed oil has to. Expect the distilled component to be quantified — a percentage describes the oil, but only milligrams of a named compound per serving describes what a serving contains. And treat any single process word as a starting point rather than a conclusion, since none of them is independently certified.

Why does a blend need two separate extractions?

Because the two processing windows do not overlap — and that is the sharpest way to see why this product is made the way it is. A still runs at around 100 °C, which is entirely routine for the oregano oil being produced inside it, since that oil is defined by being able to survive the journey. Thymoquinone, meanwhile, is described as heat-sensitive with degradation reported around 80–100 °C, and cold pressing deliberately stays down at roughly 40–49 °C. The temperature that is normal for one component sits at or above the top of the band described as degrading for the other.

Two oils in one bottle whose safe processing temperatures are more than 50 °C apart cannot be made together. They are extracted separately, on different equipment, at different temperatures, and combined only afterwards and cold. And the finished blend then inherits the stricter of the two limits for the rest of its life — which is the practical reason the same instruction appears across this site: never add the drops to a hot drink, and keep the bottle at a steady room temperature rather than near a stove or a sunny window. The storage page covers what that looks like day to day.

Where does WaveDrops sit?

On both sides of this page at once, deliberately — one distilled component and one pressed component, each made by the method its chemistry requires. The oregano is wild-harvested Greek Origanum vulgare, steam-distilled and standardised to 80%+ carvacrol. The black seed oil is cold-pressed Nigella sativa, used as a functional edible base that contributes thymoquinone in its own right rather than a filler carrier oil chosen because it was cheap. They meet after extraction, not during it. The label serving is 2 drops, up to 3 times a day, always diluted in water or juice and taken with food, delivering about 18 mg of carvacrol and ~0.9 mg of thymoquinone, with roughly 200 servings in the 10 mL amber-glass dropper. The reason those milligram figures are printed at all traces straight back to the yield asymmetry above: the distilled fraction is scarce and potent, so the only informative way to describe it is by weight per serving. A fuller breakdown sits on the ingredients page.

Three claims this page will not repeat

Extraction-method articles carry a few well-travelled lines that do not survive contact with the chemistry, so they are named here rather than quietly inherited.

"Cold-pressed oils are purer and retain more of the plant than distilled ones." The two methods recover different oils from different raw materials, so there is no shared baseline to be purer than; a cold-pressed oil retains more of the seed precisely because it filters nothing. "Cold pressing preserves 100% of the nutrients." No process preserves everything, pressing exposes oil to oxygen and mechanical shear, and the figure is quoted without a measurement on either side. "Steam distillation removes impurities, so distilled oil is the cleaner product." Distillation selects by volatility alone, which is indifferent to whether a volatile molecule is desirable, so it is a separation and not a cleaning step. As always on this site, declining to repeat a number is not a claim that the process makes no difference — it is a claim that a figure should have a source before it is printed.

Next, read what carvacrol is for the compound the distillation exists to recover, or how to choose a quality oregano oil for the buyer's checklist this all feeds into. You can also return to the WaveDrops homepage.

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These statements have not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease.