This is a working overview of freeze-drying, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2026-04-22 and is reviewed periodically as new material appears.
A freeze-dryer consists of a vacuum chamber, temperature-controlled shelves, a condenser, and a vacuum pump. Vials, ampoules, or bulk trays hold the product during the cycle. The condenser traps water vapor as ice at a temperature lower than the product. Cycle development balances shelf temperature, chamber pressure, and time. Scale-up can be difficult because heat and mass transfer change with equipment size, so process analytical tools and conservative validation are often used.
Lyophilization is a dehydration technique in which a product is frozen and the solvent is removed under reduced pressure. The low pressure allows ice to sublimate directly into vapor without passing through a bulk liquid phase. This differs from conventional drying, where heat drives evaporation and can damage heat-sensitive structures. The process is used for biological materials, pharmaceutical formulations, and some foods. Its main advantage is preservation of porous structure and rapid reconstitution.
Freezing is the first stage and sets the ice structure that later becomes the pore network. The formulation is cooled below its freezing point, often with a controlled ramp, and solutes concentrate as ice forms. Primary drying then lowers chamber pressure and supplies heat to sublime the ice. The product temperature must stay below its collapse or eutectic temperature to prevent structural loss. Secondary drying raises the temperature modestly to remove bound water and achieve a low residual moisture.
The process generally proceeds in three stages: freezing, primary drying, and secondary drying. During freezing, controlled cooling converts water into ice and may also crystallize or vitrify solutes. In primary drying, the pressure is lowered below the triple point, and heat is supplied so ice sublimes directly to vapor. Secondary drying removes water that remains bound to the solid matrix, yielding a low final water content. Product temperature must stay below the collapse or glass transition temperature to maintain structure. Cycle design therefore balances shelf temperature, chamber pressure, and time.
Freeze-drying is used for materials whose activity or structure depends on low temperature and low water content. Examples include certain biologics, diagnostic reagents, starter cultures, coffee, and porous inorganic precursors. The dried product forms a cake whose porosity aids rapid wetting and dissolution. Main drawbacks are high energy use, long cycle times, and sensitivity to formulation and equipment variation. Questions remain about how freezing rates and ice morphology affect batch uniformity, especially when moving from laboratory to production scale.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | freeze-drying, lyophilisation, cryodesiccation | Lyophilization is common in pharmaceutical literature. |
| Typical chamber pressure during primary drying | 0.05–0.5 mbar (5–50 Pa) | Must remain below the triple point of water. |
| Typical shelf temperature during freezing | −40 to −20 °C | Lower temperatures may be used for eutectic systems. |
| Typical residual moisture after secondary drying | 0.5–3% w/w | Product-dependent; low moisture improves stability but can cause over-drying. |
| Typical analytical method for residual moisture | Karl Fischer titration or loss on drying | Thermogravimetric methods are also used. |
Freeze-drying is distinct from simple evaporation and from spray drying. Evaporation removes water at temperatures above freezing, while spray drying rapidly dries droplets in a heated gas stream. Lyophilization avoids high temperatures, which can be useful for heat-sensitive materials such as proteins, vaccines, and some foods. The porous cake produced by sublimation dissolves or rehydrates more quickly than a dense dried mass. Not all materials tolerate freezing or the pH shifts that can occur as solutes concentrate during ice formation.
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and fixes the structure of the sample. After freezing, primary drying lowers pressure so ice changes directly to vapor without passing through a liquid phase. Secondary drying then removes bound water that remains after ice sublimation. The result is a dry, porous solid that often retains its original shape.
The process relies on the phase diagram of water, where the triple point marks the conditions at which ice, liquid water, and vapor coexist. By maintaining pressure below this point, typically around 0.01 to 0.1 millibar, sublimation becomes the dominant mechanism. Formulations often include excipients such as sugars or polymers that act as lyoprotectants and bulking agents. These additives help preserve the structure of the active ingredient and prevent collapse during drying. The choice of excipient and freezing rate influences the final cake morphology and stability.
Industries use lyophilization for pharmaceuticals, biological products, and food preservation. In the pharmaceutical sector, it extends the shelf life of injectable drugs, vaccines, and proteins that are unstable in aqueous solution. Food manufacturers apply freeze-drying to coffee, fruits, and ready meals to retain flavor and texture. The process is energy-intensive and requires specialized equipment, which limits its use to high-value products. Ongoing research examines how formulation and process parameters affect the quality of the final dried product.
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== Human proteins containing this domain == SLC6A1, SLC6A2, SLC6A3, SLC6A4, SLC6A5, SLC6A6, SLC6A7, SLC6A8, SLC6A9, SLC6A11, SLC6A12, SLC6A13, SLC6A14, SLC6A15, SLC6A16, SLC6A17, SLC6A18, SLC6A19, SLC6A20
NAD+ + a quinol The 3 substrates of this enzyme are NADH, H+, and a quinone (electron acceptor), whereas its two products are NAD+ and a quinol (reduced acceptor). This enzyme is found in aerobic bacteria and the mitochondria of yeast and plants. In many other organisms (notably the mitochondria of animals), there is a similar enzyme called respiratory complex I, which differs from this enzyme in that it also pumps protons. An important example of this reaction is:
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These enzymes cleave the β-lactam ring, an essential component of β-lactam antibiotics that are recognized by and bound to PBPs. Carbapenemases are divided into different classes, depending on the structure of the enzyme and the mechanism by which they hydrolyze the β-lactam ring. The two broad categories of carbapenemases are serine-carbapenemases, which contain serine at the active site, and metallocarbapenemases, which contain zinc at the active site. Class A carbapenemases are serine carbapenemases and are encoded on either the chromosome of the bacteria or a plasmid. A serine at position 70 at the active site of this class of enzymes is required for hydrolysis of β-lactams to occur. Class D carbapenemases, also referred to as the OXA β-lactamases, are serine β-lactamases. They are encoded on plasmids and contain a large variability in amino acid sequence. The resistance mechanism for class D carbapenemases is caused by the formation of an acyl intermediate when breaking the β-lactam ring. Class B carbapenemases are metallolactamases and require a zinc at the active site for hydrolysis. A clinical isolate of E. coli from the sputum sample of a patient admitted to a Beijing hospital was found to acquire resistance to carbapenem through mutations not previously observed. It involved a mutation of a regulator gene marR and the expression of a normally nontranslated membrane porin yedS; both mutations were demonstrated to have effects on the ability of this strain of E.coli to resist carbapenems.
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== Function == The protein encoded by this gene belongs to the basic helix-loop-helix family of transcription factors. This gene product is one of two closely related family members, the HAND proteins are expressed within the developing ventricular chambers, cardiac neural crest, endocardium (HAND2 only) and epicardium (HAND2 only). HAND1 is expressed with myocardium of the primary heart field and plays an essential but poorly understood role in cardiac morphogenesis. HAND1 works jointly with HAND2 in cardiac development of embryos based on a crucial HAND gene dosage system. If HAND1 is over or under expressed then morphological abnormalities can form; most notable are cleft lips and palates. Expression was modeled with a knock-in of phosphorylation to turn on and off gene expression which induced the craniofacial abnormalities. Knock-out experimentation on mice caused death and severe cardiac malformations such as failed cardiac looping, impaired ventricular development and defective chamber septation. This aids in the implication that HAND1 expression is a factor to patients with congenital heart disease. However, a lack of HAND1 in the distal regions of the Neural Crest has no effect on cranial feature formation. Mutation of HAND1 has been shown to hinder the effect of GATA4, another vital cardiac transcription factor, and is associated with congenital heart disease.
Cligosiban (INNTooltip International Nonproprietary Name; developmental code names IX-01 and PF-3274167) is an oxytocin receptor antagonist which is or was under development for the treatment of premature ejaculation. It is taken orally. The drug is a small molecule or non-peptide and is a potent, highly selective, and brain-penetrant antagonist of the oxytocin receptor. Cligosiban was originated by Pfizer and is under development by Ixchelsis and Chorus Group. As of December 2019, it is in phase 2 clinical trials. However, another source lists the drug's development as having been discontinued. The drug failed to show effectiveness in a phase 2b trial.
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The presence of breast implants currently presents no contraindication to breast feeding, and there is no evidence to support that the practice may present health issues to a breastfeeding infant. Women with breast implants may have functional breast-feeding difficulties; mammoplasty procedures that feature periareolar incisions are especially likely to cause breastfeeding difficulties. Surgery may also damage the lactiferous ducts and the nerves in the nipple-areola area. Functional breastfeeding difficulties arise if the surgeon cut the milk ducts or the major nerves innervating the breast, or if the milk glands were otherwise damaged. Milk duct and nerve damage are more common if the incisions cut tissue near the nipple. The milk glands are most likely to be affected by subglandular implants and by large-sized breast implants, which pinch the lactiferous ducts and impede milk flow. Small-sized breast implants and submuscular implantation cause fewer breast-function problems; however, it is impossible to predict whether a woman who undergoes breast augmentation will be able to successfully breast feed since some women are able to breast-feed after periareolar incisions and subglandular placement and some are not able to after augmentation using submuscular and other types of surgical incisions.
=== 1997 constitutional crisis === The Cherokee Nation was seriously destabilized in May 1997 in what was variously described as either a nationalist "uprising" or an "anti-constitutional coup" instigated by Joe Byrd, the Principal Chief. Elected in 1995, Byrd became locked in a battle of strength with the judicial branch of the Cherokee tribe. The crisis came to a head on March 22, 1997, when Byrd said in a press conference that he would decide which orders of the Cherokee Nation's Supreme Court were lawful and which were not. A simmering crisis continued over Byrd's creation of a private, armed paramilitary force. On June 20, 1997, his private militia illegally seized custody of the Cherokee Nation Courthouse from its legal caretakers and occupants, the Cherokee Nation Marshals, the Judicial Appeals Tribunal, and its court clerks. The courts demanded the courthouse's return, but Byrd refused. The Federal authorities of the United States initially refused to intervene because of potential breach of tribal sovereignty. Byrd was required to attend a meeting in Washington, D.C. with the Bureau of Indian Affairs, at which he was compelled to reopen the courts. Byrd served the remainder of his term but lost the 1999 election for Principal Chief to Chad Smith. He was later elected to the Tribal Council in 2013. A new constitution was drafted in 1999 that included procedures for voters to remove officials from office, changed the structure of the tribal council, and removed the need to ask the Bureau of Indian Affairs' permission to amend the constitution.
== Capsaicinoids == The most commonly occurring capsaicinoids are capsaicin (69%), dihydrocapsaicin (22%), nordihydrocapsaicin (7%), homocapsaicin (1%), and homodihydrocapsaicin (1%). Capsaicin and dihydrocapsaicin (both 16.0 million SHU) are the most pungent capsaicinoids. Nordihydrocapsaicin (9.1 million SHU), homocapsaicin and homodihydrocapsaicin (both 8.6 million SHU) are about half as hot. There are six natural capsaicinoids (table below). Although vanillylamide of n-nonanoic acid (Nonivamide, VNA, also PAVA) is produced synthetically for most applications, it does occur naturally in Capsicum species.
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Yes, the terms are generally interchangeable. Lyophilization is more common in pharmaceutical and laboratory contexts, while freeze-drying appears widely in food science and general writing. Both describe removal of solvent by sublimation under vacuum after freezing.
Reduced pressure keeps the process below the triple point of water, so ice can sublimate directly to vapor. It also lowers the temperature needed for drying, which helps preserve heat-sensitive materials. Without vacuum, melting or boiling could occur instead of controlled sublimation.
The rate depends on heat transfer to the product and mass transfer of vapor through the dried layer. A cold condenser, adequate vacuum, and suitable shelf temperature all influence speed. Formulation properties such as solid content and collapse temperature also set practical limits.
Yes. Lyophilization and freeze-drying are synonyms for the same vacuum-assisted sublimation process. The term lyophilization is more common in pharmaceutical and laboratory settings, while freeze-drying is widely used in food and general contexts.