Definition
Freeze-drying: removing water from a frozen solution by sublimation under vacuum to stabilise a peptide as a dry powder.
Lyophilization, or freeze-drying, removes water from a peptide solution in three stages: freezing, primary drying, in which ice sublimes directly to vapour under vacuum, and secondary drying, which removes bound water. The result is a dry cake or film with low residual moisture. Removing water slows the reactions that degrade peptides in solution, including hydrolysis, deamidation and some oxidation pathways, so lyophilised material can be stored for months to years at −20 °C. A small mass of lyophilised peptide can look like very little material or coat the vial wall; this is normal. Lyophilised peptides are hygroscopic, so vials should reach room temperature before opening to prevent condensation.