The short version of secondary drying fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-05-11. Anything still debated is marked as such rather than presented as settled.
The low pressure used during drying allows water vapor to move from the ice surface to a cold condenser. Energy supplied as heat drives sublimation but must stay below the collapse temperature of the frozen matrix. If the product becomes too warm, the frozen structure may soften or melt, reducing pore formation and slowing drying. Formulations often include bulking agents, stabilizers, or buffers to support a rigid cake. The final moisture content depends on formulation, freezing rate, and the length of secondary drying.
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 is a dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen to convert liquid water into ice. Next, the pressure is reduced below the triple point of water so that ice changes directly into vapor without passing through a liquid phase. This step is called primary drying. The result is a porous solid or cake that retains the original shape of the frozen solution.
After primary drying, secondary drying removes water that remains bound to the material. This stage raises the shelf temperature while maintaining low pressure, which encourages desorption of unfrozen water. Residual moisture can be reduced to a low percentage, improving stability for many products. The process parameters, including freezing rate, shelf temperature, and chamber pressure, influence the final pore structure and reconstitution behavior. Control of these variables helps prevent collapse or meltback during drying.
| Property | Value | Notes |
|---|---|---|
| Primary phase change | Sublimation | Ice changes directly to vapor under reduced pressure |
| Typical chamber pressure | 0.01–0.5 mbar (1–50 Pa) | Below the triple point of water; product-specific |
| Typical product temperature during primary drying | −40 °C to −10 °C | Kept below collapse temperature |
| Typical residual moisture | 0.5–3% w/w | Target range varies by formulation and use |
| Common synonyms | Freeze-drying; lyophilisation | Lyophilization is the US spelling |
Lyophilization, also called freeze-drying, is a dehydration process in which a solvent, usually water, is frozen and then removed by sublimation under reduced pressure. The method preserves heat-sensitive materials that would degrade in conventional drying. Large-scale use grew during the mid-twentieth century for blood plasma and antibiotics, and it later expanded to vaccines, enzymes, foods, and advanced materials. The process produces a dry, porous solid that usually reconstitutes rapidly. It is distinct from simple evaporation because the solvent bypasses the liquid phase during primary removal.
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.
The process usually has three stages: freezing, primary drying, and secondary drying. Freezing sets the ice crystal structure and can determine pore size in the final cake. Primary drying removes free ice by sublimation at low pressure and low shelf temperature. Secondary drying removes bound water by raising the shelf temperature, although some water may remain as part of the solid. Cycle parameters depend on formulation, fill volume, vial type, and equipment performance.
The physical chemistry of freezing influences whether a formulation forms an amorphous glass or a crystalline solid. Amorphous systems can collapse if product temperature rises above the glass transition temperature of the freeze concentrate. Crystalline systems may show eutectic melting, where ice and solute melt together at a fixed temperature. Formulators add bulking agents, lyoprotectants, and buffers to preserve structure and biological activity. The optimum cycle keeps product temperature below critical thresholds during primary drying while allowing efficient sublimation.
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.
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.
=== Addiction === PCP is self-administered and induces ΔFosB expression in the D1-type medium spiny neurons of the nucleus accumbens, and accordingly, excessive PCP use is known to cause addiction. PCP's rewarding and reinforcing effects are at least partly mediated by blocking the NMDA receptors in the glutamatergic inputs to D1-type medium spiny neurons in the nucleus accumbens. PCP has been shown to produce conditioned place aversion and conditioned place preference in animal studies.
== History == In 2013, trastuzumab emtansine was approved in the United States for the treatment of adults with HER2-positive, metastatic breast cancer who previously received trastuzumab and a taxane, separately or in combination. Referred to as T-DM1 during clinical research, trastuzumab emtansine was reviewed under the FDA's priority review program. The safety and effectiveness of trastuzumab emtansine were evaluated in a clinical study of 991 patients randomly assigned to receive trastuzumab emtansine or lapatinib plus capecitabine, another chemotherapy drug. Patients received treatment until either the cancer progressed or the side effects became intolerable. The study was designed to measure progression-free survival, the length of time patients lived without the cancer progressing, and overall survival, the length of time patients lived before death. Results showed that patients treated with trastuzumab emtansine had a median progression-free survival of 9.6 months compared to 6.4 months in patients treated with lapatinib plus capecitabine. The median overall survival was 30.9 months in the trastuzumab emtansine group and 25.1 months in the lapatinib plus capecitabine group. The U.S. Food and Drug Administration (FDA) approved trastuzumab emtansine in February 2013, and granted the application for Kadcyla to Genentech. The FDA granted the application for trastuzumab emtansine priority review and breakthrough therapy designations. In 2013, trastuzumab emtansine was approved in the UK, and the EU.
Health Canada has concluded that there is no health risk to Canadians from use of available soy and oyster sauces. Because continuous lifetime exposure to high levels of 3-MCPD could pose a health risk, Health Canada has established 1.0 part per million (ppm) as a guideline for importers of these sauces, in order to reduce Canadians' long-term exposure to this chemical. This is considered to be a very safe level.
Sources: en.wikipedia.org
In some cultures, people who have been breastfed by the same woman are milk-siblings who are equal in legal and social standing to a consanguineous sibling. Islam has a complex system of rules regarding this, known as Rada (fiqh). Like the Christian practice of godparenting, milk kinship established a second family that could take responsibility for a child whose biological parents came to harm. "Milk kinship in Islam thus appears to be a culturally distinctive, but by no means unique, institutional form of adoptive kinship." In Western countries, differences in breastfeeding practices have also been observed according to the affiliation or practice of Christian religions; unaffiliated and Protestant women exhibit higher rates of breastfeeding.
Fumarate, produced from the purine nucleotide cycle, is an intermediate of TCA cycle and enters the mitochondria by converting into malate and utilizing the malate shuttle where it is converted into oxaloacetic acid (OAA). During exercise, OAA either enters into TCA cycle or converts into aspartate in the mitochondria. As the purine nucleotide cycle produces ammonia (see below in ammonia synthesis), skeletal muscle needs to synthesize glutamate in a way that does not further increase ammonia, and as such the use of glutaminase to produce glutamate from glutamine would not be ideal. Also, plasma glutamine (released from the kidneys) requires active transport into the muscle cell (consuming ATP). Consequently, during exercise when the ATP reservoir is low (ADP>ATP), glutamate is produced from branch-chained amino acids (BCAAs) and α-ketoglutarate, as well as from alanine and α-ketoglutarate. Glutamate is then used to produce aspartate. The aspartate enters the purine nucleotide cycle, where it is used to convert IMP into S-AMP.
=== 2021 poisoning at Darmstadt Technical University === In August 2021, several people fell severely ill after consuming drinks at building L2.01 at the Lichtwiese Campus of Darmstadt Technical University, Germany. Seven showed severe symptoms, two were transported to a hospital in Frankfurt am Main, and a 30-year-old person was, for a time, in a critical state. Butane-1,4-diol had been detected in milk packages, as well as in water filters. At the location, detectives also found bromophenols and dicyclohexylamine.
Sources: en.wikipedia.org
He then may or may not have been induced to sign it", since it ran counter to Faisal's other public and private statements at the time. A 1 March interview by Le Matin quoted Faisal as saying: This feeling of respect for other religions dictates my opinion about Palestine, our neighbor. That the unhappy Jews come to reside there and behave as good citizens of this country, our humanity rejoices given that they are placed under a Muslim or Christian government mandated by The League of Nations. If they want to constitute a state and claim sovereign rights in this region, I foresee very serious dangers. It is to be feared that there will be a conflict between them and the other races. Referring to his 1922 White Paper, Churchill later wrote that "there is nothing in it to prohibit the ultimate establishment of a Jewish State." And in private, many British officials agreed with the Zionists' interpretation that a state would be established when a Jewish majority was achieved. When Chaim Weizmann met with Churchill, Lloyd George and Balfour at Balfour's home in London on 21 July 1921, Lloyd George and Balfour assured Weizmann "that by the Declaration they had always meant an eventual Jewish State," according to Weizmann minutes of that meeting. Lloyd George stated in 1937 that it was intended that Palestine would become a Jewish Commonwealth if and when Jews "had become a definite majority of the inhabitants", and Leo Amery echoed the same position in 1946.
== Hemocyanin == Hemocyanin is a respiratory pigment that uses copper as its oxygen-binding molecule, as opposed to iron with hemoglobin. Hemocyanin is found in both arthropods and Mollusca, however it is thought that the molecule independently evolved in both phyla. There are several other molecules that exist in arthropods and Mollusca that are similar in structure to hemocyanin but serve entirely different purposes. For example, there are copper-containing tyrosinases that play significant roles in immune defense, wound healing, and the arthropod's cuticle. Molecules similar to hemocyanin in structure are grouped in under the hemocyanin superfamily.
== Civilian airfields == A few civilian airfields, such as Clinton-Sherman Airport, were originally SAC bases. The long-length runways were maintained, as well as the Christmas tree alert structure for possible reuse by SAC forces in the event of nuclear war.
=== Axon growth regulation === Crosslinking anti-Thy-1 Ab can promote neurite outgrowth which is dependent on G{alpha}i and L- and N-type calcium channel activation. The ligand for promotion of neurite outgrowth on astrocytes is not yet identified, but the inhibitory ligand has been suggested to be integrins. Thy1 is one of the known ligands of beta 3 integrins. Interaction of thy1 expressed on maturing axons with beta 3 integrins expressed on mature astrocytes is one of the causes of halting of axon growth.
Sources: en.wikipedia.org
Lyophilization relies on sublimation, so water moves from solid ice to vapor without becoming liquid. The material is frozen, pressure is reduced, and controlled heat is supplied. Vapor is captured on a cold condenser, leaving a dry porous solid.
The process has three main stages: freezing, primary drying, and secondary drying. Freezing sets the ice structure, primary drying removes free ice, and secondary drying removes bound water. Each stage uses specific temperature, pressure, and time settings.
No, it is a drying method rather than a sterilization method. Removing water can limit microbial growth, but it does not reliably kill microorganisms. Sterility must come from separate steps such as filtration, heat treatment, or aseptic processing.
Lyophilization removes water by sublimation from a frozen material, while evaporation changes liquid water into vapor. The low-pressure freezing step avoids the liquid phase and can preserve heat-sensitive structures.