If you've browsed research peptide listings, you'll have seen the word lyophilised a lot. It simply means freeze-dried. Lyophilisation is the process of removing water from a material by freezing it and then turning the ice straight into vapour, without letting it melt first.
This guide explains how that process works, stage by stage. It's a general reference on a laboratory and manufacturing technique. It doesn't describe how any particular product was made, and it doesn't cover dissolving, preparing or using any material. We don't provide instructions of that kind.
The short version
| Stage | What happens | Main aim |
|---|---|---|
| 1. Freezing | The solution is cooled until the water turns to ice | Lock the material in a solid frozen structure |
| 2. Primary drying | Pressure is lowered and gentle heat added, so ice turns straight to vapour (sublimation) | Remove most of the water |
| 3. Secondary drying | Temperature is raised a little further under vacuum | Remove water still bound to the solid |
| 4. Sealing | Vials are closed, often while still under vacuum or dry gas | Keep moisture and air out |
Why materials are freeze-dried
Many substances, including peptides, are less stable when water is present. Water can take part in slow chemical changes, and a liquid is harder to store and transport than a dry solid. Removing the water by ordinary heating would often damage a delicate material, so freeze-drying takes a gentler route: it removes water at low temperature.
That's why freeze-drying is widely used for laboratory reagents, reference materials and many other sensitive substances, not just peptides. It's also used in the food industry, for things like freeze-dried coffee.
Stage 1: freezing
The process starts with the material dissolved in water, usually filled into vials or trays. The material is cooled on shelves inside a freeze-dryer until it's completely frozen, often well below −30 °C.
How the freezing is done matters. Freezing quickly tends to make many small ice crystals, while freezing slowly makes fewer, larger ones. The size of the ice crystals affects how easily water vapour can escape later, so manufacturers control the cooling rate carefully. Some processes include an annealing step, where the frozen material is warmed slightly and cooled again to encourage more even ice crystals.
The key idea is that, once frozen, the material is held in place in a solid structure between the ice crystals.
Stage 2: primary drying (sublimation)
Next, the chamber's air is pumped out to create a strong vacuum, and the shelves are warmed very gently. Under low pressure, ice doesn't melt. It goes straight from solid to vapour, a change called sublimation.
The water vapour travels to a very cold surface called the condenser, where it freezes again and is trapped, so it can't return to the material.
This is usually the longest stage, often taking many hours or even days. The temperature has to stay below a critical point for the material. If it rises too far, the structure can soften and collapse, which is why the process is monitored closely throughout.
By the end of primary drying, most of the water has gone, and what remains is a dry, porous solid that keeps roughly the shape of the frozen material.
Stage 3: secondary drying (desorption)
Even after the ice has gone, some water molecules remain bound to the solid. In secondary drying, the shelf temperature is raised a little higher, still under vacuum, to drive off this bound water. This step is called desorption.
Freeze-dried powders are rarely completely free of water. A small amount usually remains, which is why certificates often report a separate water content row. Our guide to peptide purity vs peptide content explains how water content fits alongside the other figures on a certificate.
Stage 4: sealing the vials
At the end of the cycle, vials are typically sealed inside the freeze-dryer. Many machines can press the stoppers down while the chamber is still under vacuum or filled with a dry gas such as nitrogen. That keeps moisture and air away from the dry material. Caps or crimp seals are then added outside the machine.
What the result looks like
A freeze-dried material in a vial is often called a cake. Depending on the material and the process, it can look like:
- a solid white puck that fills the bottom of the vial,
- a looser powder, or
- a small amount of material that's hard to see, especially in low-quantity vials.
Small cracks, a slightly shrunken cake, or powder that has moved around in transit are common and are generally a matter of appearance. The look of a cake on its own doesn't tell you what a material is or how pure it is. That's what the analytical tests on a certificate are for.
Words you might see
- Lyophilised / lyophilized: freeze-dried. The "s" spelling is British, the "z" spelling American.
- Lyophilisate: the dry material left after freeze-drying.
- Sublimation: a solid turning straight into a vapour without melting.
- Desorption: removing water that's bound to a solid's surface.
- Condenser: the very cold part of a freeze-dryer that traps the water vapour.
- Collapse: loss of the dried structure if the material gets too warm during drying.
- Excipient: an added substance, such as a sugar, that some formulations include to help the cake hold its structure.
- Counter-ion: an ion, such as acetate, that sits alongside a peptide in its salt form. See our guide to peptide salt forms.
Keeping a freeze-dried material dry
Because freeze-drying works by removing water, the dry material can pick moisture back up from the air if a vial is left open or poorly sealed. Our guide to storing lyophilised peptides covers keeping sealed vials dry and away from light.
For how to read the rows on a certificate, including water content, see how to read a peptide certificate of analysis. We publish Manufacturer COAs (SENOBIO), listed by batch, on our COAs page. Our vial labels don't currently show a lot number, so a certificate may not be for the lot you receive. See also our FAQ, or browse Research Peptides UK.
For laboratory research use only. Not for human or veterinary use. 18+
