Lyophilisation: freeze-drying, explained

Lyophilisation is freeze-drying: removing water from a frozen product so it ends up as a dry, stable powder.

Pronounced lie-OFF-ill-eye-ZAY-shun. Spelled "lyophilization" in American English.

The process, step by step

1. Freeze. The liquid is frozen solid, so the water turns to ice.
2. Primary drying. The pressure is lowered to a near-vacuum. The ice turns straight into vapour without melting, which is called sublimation.
3. Secondary drying. The temperature is raised gently to remove the last traces of water bound to the molecules.
4. Seal. The vial is sealed, often under dry gas, so moisture can't get back in.

Why peptides come as powder

Water lets molecules move around and react, which slowly breaks peptides down. Taking the water out locks them in place, so a lyophilised powder keeps far longer than the same peptide in liquid. The powder is often light and fluffy, sometimes called a "cake", and can look like a tiny amount in the vial.

How labs store lyophilised peptides

• Cold: usually in a freezer for long-term storage.
• Dry: sealed, and allowed to reach room temperature before opening, so condensation doesn't form inside.
• Dark: away from direct light.

Freeze-drying beyond the lab

The same process makes instant coffee, astronaut food and many vaccines and medicines shelf-stable.