The phrase "cold pressed" gets used so often on labels that it can feel like a vague quality claim. It isn't — it describes a specific mechanical process. Understanding how a press actually works makes the quality differences between products legible.
The Basic Mechanism
A screw press (the most common type for seed oils) consists of a rotating screw inside a cylindrical barrel. Seeds or nuts are fed from one end. As the screw rotates, it moves material forward while the space around the screw progressively decreases, squeezing the material against the barrel walls and a small die opening at the far end.
Oil is pressed out through the barrel's perforated walls and collects below. The remaining solid — called the press cake or expeller cake — exits from the far end. For coconut oil, the press cake is copra meal. For sesame or groundnut, it's an oil-bearing cake still used as animal feed or processed further.
The entire process is continuous: seeds in, oil and cake out, no batches.
Why Temperature Is the Critical Variable
Friction is unavoidable in mechanical pressing. As material is compressed and moved, heat is generated. The amount of heat depends on:
Screw speed (RPM): Faster rotation = more friction = more heat. A press running at 200 RPM generates significantly more heat than one running at 60 RPM.
Die opening size: A smaller die forces more pressure on the material to exit, generating more heat. Larger openings reduce pressure and heat but also reduce oil yield.
Moisture content of the seed: Drier seeds generate more heat during pressing. Seeds with appropriate moisture content for their type cool the friction slightly.
Press design: Some presses include water cooling around the barrel. Others rely on ambient temperature and slow operation.
For cold pressing to be genuine, the temperature of the oil as it exits the barrel must stay below 50°C (some certifications require 27°C). This requires deliberate calibration — you can't just call any mechanical press "cold pressed."
What Happens to Nutrients at Different Temperatures
The compounds most sensitive to heat in seed oils:
- Vitamin E (tocopherols): Begin degrading around 70°C. Mostly stable below 50°C.
- Sesamol (in sesame): Contributes to flavour and antioxidant activity; preserved at cold-press temperatures.
- Polyphenols: Variable, but most are preserved below 50°C.
- Aromatic compounds: Some are volatile even at room temperature. Cold pressing preserves significantly more than hot extraction.
Heat isn't the only variable. Duration matters too: even at moderate temperatures, extended pressing time increases oxidation.
Seed Quality and Storage
A press run starts long before the seeds enter the machine. Seed quality determines the ceiling on oil quality. Poorly stored seeds that have already begun to oxidise will produce rancid oil regardless of how carefully the pressing is done.
For sesame and groundnut oil, the seeds should be clean, dry (but not over-dried), and pressed within a reasonable window after the previous season's harvest. Old seeds from multiple seasons ago don't produce good oil.
We verify seed quality before each pressing run — moisture content, smell, absence of mold or insect damage. A batch that doesn't meet standard doesn't go into production. The press can only do so much.
After the Press
Raw oil from the press contains fine particles, some water, and suspended solids. It's allowed to settle in a tank for 24–48 hours, after which the clear oil is separated. This is gravity settling — no centrifuge, no filter aid, no bleaching clay. The oil that results is what we put in the bottle.
The slight haziness you might notice in some cold-pressed oils is natural and harmless — fine lecithin particles that didn't fully settle. It has no bearing on quality.
