Three stages, one idea
Lyophilization works because water can sublime — go directly from solid to gas without melting — if you keep the pressure and temperature low enough. That is the whole concept. Everything else is engineering.
The three stages, in order:
- Freezing. The product is cooled until all free water has crystallized. This is fast but consequential — the ice crystal structure determines how the rest of the cycle goes.
- Primary drying. Pressure is reduced and shelf temperature raised just enough to sublimate the ice without melting it. Most of the water comes out here.
- Secondary drying. Temperature raises further to remove bound water still clinging to the peptide. This is what gets moisture below 5%.
What a good cake looks like
A properly lyophilized peptide cake is white, structurally intact, and fills the bottom of the vial in the shape of the solution it started as. It should not rattle when tilted. When reconstituted, it should dissolve cleanly in seconds, without clouding or floating particles.
Collapse: the thing we watch for
If primary drying is pushed too fast — shelf warmed before enough ice has sublimated — the remaining liquid at the ice interface passes above its collapse temperature and the cake literally deflates. You get a shrunken, glassy plug that looks like caramel. Reconstitution is slow. Stability drops.
Collapsed cakes are the single most common visible defect in lyophilized peptides. If you open a vial and the plug is noticeably smaller than the fill volume would suggest, or has a “melted candy” appearance, it has collapsed. Even partial collapse means the cycle was run hot.
Why moisture content matters more than you’d think
A peptide that retains 10% water after lyophilization is not stable at −20 °C for 24 months. The water migrates, hydrogen bonds shift, and the molecule begins to degrade — slowly, but measurably. Our spec is ≤ 8.0%. Our target is ≤ 6.0%.
Every lot we release has its Karl Fischer water result on the COA. If the number is over 6%, the cycle that ran that batch is audited before the next cycle.