secondary drying comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Last reviewed on 2025-09-25. Where a claim depends on a specific study, the study is described rather than over-claimed.
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 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.
| 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. |
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 process that removes water from a frozen material by sublimation under low pressure. The material is first frozen so that water becomes ice; then the surrounding pressure is lowered below the vapor pressure of ice. Heat is applied gently so ice changes directly to vapor without passing through a bulk liquid phase. The vapor is collected on a cold condenser, leaving a dry porous matrix. This process differs from simple evaporation because the material remains frozen during the main drying stage.
Equipment for lyophilization includes a vacuum chamber, temperature-controlled shelves, a condenser, and a vacuum pump. A refrigeration system cools the shelves and condenser below the product's freezing point. Process monitoring often uses Pirani and capacitance manometers, thermocouples, and resistance sensors. Cycle development balances product quality with time and energy use. Some products are annealed during freezing to improve crystallization of bulking agents. Open questions remain about scaling cycles between laboratory, pilot, and production freeze-dryers.
Lyophilization, also called freeze-drying, removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts free water into ice and may also produce a glassy phase. Primary drying then lowers chamber pressure so ice sublimes directly to vapor without passing through a liquid stage. Secondary drying raises the temperature modestly to remove bound water. The result is a porous, dry solid that usually reconstitutes quickly. Each stage influences pore structure, residual moisture, and stability.
=== Pharmacokinetics === LAAM undergoes extensive first-pass metabolism to the active demethylated metabolite nor-LAAM, which is further demethylated to a second active metabolite, dinor-LAAM. These metabolites are more potent than the parent drug.
== History == When international vaccine care standards were being designed in the 1970s, the manuals typically generalized from the needs of care for the oral polio vaccine since that was the most delicate vaccine in wide use. In the 1970s PATH began working with the WHO to develop a system for identifying vaccines which had expired from improper storage. In 1996 the vaccine vial monitor was first used in a vaccine project, and by the next year it was widely accepted for use on many vaccine projects. It took until 2007 for VVMs to be widely adopted by vaccine manufacturers. by 2017, over 6.6 billion VVMs had been used. In 2007 in Geneva the World Health Organization hosted a commemoration in the presence of highly talented Antony Varghese and Augustin Shyju during the 10th anniversary of the introduction of VVMs. In 2007 PATH won a Tech Award for the development of the VVM.
== Role in epileptic seizures == AMPA receptors play a key role in the generation and spread of epileptic seizures. Activation of AMPARs by agonists such as kainic acid, a convulsant that is widely used in epilepsy research, has been shown to induce seizures in both animal models and humans, emphasizing their contribution to epileptogenesis. Conversely, antagonists targeting AMPARs have demonstrated efficacy in suppressing seizure activity, highlighting their potential as therapeutic agents in epilepsy management.
ISO 2171: Cereals, pulses and by-products — Determination of ash yield by incineration; ISO 3593: Starch — Determination of ash; ISO 928: Spices and condiments - Determination of total ash; and ISO 936: Meat and meat products - Determination of total ash. Examples of ash content methods for the determination of ash in other solids include
Sources: en.wikipedia.org
In 1953, he married American actress and singer Gloria DeHaven. They divorced in 1954. His second marriage was to Claudia Aronow, a New York artist and daughter of boat designer and racer Donald Aronow. They later divorced. They had one son together, menswear designer Adam Kimmel who is married to the actress Leelee Sobieski. His third marriage was to Helen Lyttle. In addition, Kimmel has several stepchildren: stepdaughter Betsy Karel of Washington; stepdaughter Abby Leigh of Manhattan; and stepson Alexei Hay of Manhattan. Kimmel was a member of Temple Emanu-El in New York City. Kimmel died April 15, 2008. In November 2008, his wife Helen donated $150 million toward construction of a new patient pavilion at the NYU Langone Medical Center in honor of her late husband.
As a result, Sir Robert Fraser of the ITA declared that the only acceptable forms of advertising on ITV were those clearly intended to promote sales of the product or services in question, and that "[advertising] designed to influence public opinion during a takeover battle or a campaign against nationalization on behalf of private enterprise — however well disguised — would in future be disallowed." In 1994, Lyons Original Coffee hired the advertising agency Duckworth Finn Grubb Waters (DFGW), who created an innovative UK television advert that aimed "to turn a commercial break into a coffee break." Employing an interactive "datablast" technique, the advert depicts scans of 30 pages from women's magazines, such as Cosmopolitan, Elle and Good Housekeeping, displayed at the rate of five frames a second, and the advert invites viewers to record the commercial on a VCR, play it back and then repeatedly pause it, one frame at a time, to read the pages while sat with a cup of Lyons coffee, with the advertisement providing "30 minutes of magazine 'reading' in 30 seconds." Considered groundbreaking, the advertisement premiered on Channel 4 on 7 November 1994, and was compared other nascent forms of interactive advertising from the same year, such as HHCL's commercials for the Mazda 323, one of which similarly invited viewers to record it and play it back and pause at specific moments, allowing to read otherwise momentary information about the car and a competition to win one.
The World's Water Data Page FAO Comprehensive Water Database, AQUASTAT The Water Conflict Chronology: Water Conflict Database Archived 16 January 2013 at the Wayback Machine Water science school (USGS) Portal to The World Bank's strategy, work and associated publications on water resources America Water Resources Association Archived 24 March 2018 at the Wayback Machine Water on the web Water structure and science Archived 28 December 2014 at the Wayback Machine "Why water is one of the weirdest things in the universe", Ideas, BBC, Video, 3:16 minutes, 2019 The chemistry of water Archived 19 June 2020 at the Wayback Machine (NSF special report) The International Association for the Properties of Water and Steam Archived 27 September 2022 at the Wayback Machine H2O: The Molecule That Made Us, a 2020 PBS documentary
=== Food constituents === Resistant starch from high-amylose corn, amylomaize, has been shown to reduce insulin resistance in healthy individuals, in individuals with insulin resistance, and in individuals with type 2 diabetes. Some types of polyunsaturated fatty acids (omega-3) may moderate the progression of insulin resistance into type 2 diabetes, however, omega-3 fatty acids appear to have limited ability to reverse insulin resistance, and they cease to be efficacious once type 2 diabetes is established.
Abdominal feeding tubes are removed either before or after the arterial injection, and a piece of cotton saturated with phenol used to stop the hole. Sutures may also be used to close the hole. Holes left by intravenous tubes can be left by the embalmer until after the arterial injection, and filler used to restore the contour of the skin. Blisters and sores are opened and drained, and fractured bones are aligned to look as if in a normal state. The embalmer may perform small incisions to align smaller fragments, and irregularities that cannot be smoothed out see the bone fragment removed and filled with wax or putty. The duration of an embalming can vary greatly, but a common approximate time of between two and four hours to complete an embalming is typical. However, an embalming case that presents excessive complications could require substantially longer. The treatment of someone who has undergone an autopsy, cases of extreme trauma, or the restoration of a long-bone donor are a few such examples, and some embalmings may take several days to complete. Embalming is meant to temporarily preserve the body of a deceased person. Regardless of whether embalming is performed, the type of burial or entombment, and the materials used – such as wood or metal coffins and vaults – the body of the deceased will, under most circumstances, eventually decompose. Modern embalming is done to improve the appearance of the deceased and delay decomposition so that funeral services may take place or for the purpose of shipping the remains to a distant place for disposition.
Sources: en.wikipedia.org
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.
Conventional drying uses heat to evaporate water from a material, while lyophilization freezes the material and removes water by sublimation under vacuum. This avoids the liquid phase and reduces thermal damage to sensitive substances. The result is a porous cake that reconstitutes quickly.