freeze-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 2026-07-27. Where a claim depends on a specific study, the study is described rather than over-claimed.
In practice, lyophilization is slower and more energy intensive than simple drying. Cycle times can range from hours to several days depending on load, container, and formulation. Amorphous materials may require excipients that help preserve structure during freezing and drying. The method is widely used for biological materials, pharmaceuticals, and foods where heat drying would cause unacceptable change. Open questions remain about scaling cycles between laboratory and production equipment, and this gap affects technology transfer.
Lyophilization removes water by freezing a material and then lowering pressure so ice changes directly to vapor. The process relies on sublimation, the phase transition from solid to gas without an intermediate liquid state. Because the material remains frozen during primary drying, the structure often stays porous. This porous matrix can rehydrate quickly when water is added back. The low pressure also allows vapor to leave the solid matrix without boiling.
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.
The physics of lyophilization depends on phase boundaries and heat and mass transfer. During primary drying, heat supplied to the product must equal the latent heat of sublimation, while water vapor moves through the drying cake to the condenser. If shelf temperature or pressure is set too high, the ice front can exceed the collapse temperature, causing meltback or pore collapse. If conditions are too cold, drying slows and costs rise. Formulation excipients, vial geometry, and freezing rate alter these limits.
| Property | Value | Notes |
|---|---|---|
| Common synonym | Freeze-drying | Same dehydration operation |
| Typical vacuum | 10-100 Pa | Pressure during primary drying |
| Primary drying temperature | -40 to -10 °C | Below collapse temperature for many formulations |
| Cycle duration | 12-72 hours | Varies with load, container, and formulation |
| Key phase change | Sublimation | Solid ice to water vapor |
A typical cycle begins with freezing, sometimes including an annealing step to control ice crystal size. Freezing conditions influence the pore network that later allows vapor escape. During primary drying, shelf temperature and chamber pressure are set so heat enters the product while its temperature stays below the collapse or eutectic point. Secondary drying then raises the shelf temperature to desorb bound water and lower residual moisture. Cycle design depends on formulation, fill volume, container type, and equipment capability.
The physics of lyophilization couples heat transfer, mass transfer, and phase behavior. Sublimation requires a vapor pressure difference between the ice front and the chamber, and the dried layer adds resistance to vapor flow. Amorphous formulations are characterized by a glass transition temperature of the maximally freeze-concentrated solute, often denoted Tg'. Crystalline bulking agents can provide structure, while amorphous excipients stabilize labile components. Open questions remain about spatial heterogeneity, edge effects, and how laboratory cycles scale to production.
Lyophilization is a drying process in which a solvent, usually water, is removed from a frozen material by sublimation under reduced pressure. The material is first solidified, then placed under vacuum so that ice transitions directly to vapor without a bulk liquid phase. This approach suits heat-sensitive substances that would degrade during conventional evaporation. Primary drying removes unbound ice, while secondary drying reduces water that remains adsorbed to the solid matrix. The result is a porous, lightweight solid that can be reconstituted later.
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.
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.
==== Yeast Two-hybrid Screens ==== Yeast two-hybrid analyses have been adapted for protease-substrate discovery. As protease exosites play roles in protein-protein recognition and interaction, biologists have used exosites as tools to screen for protease interactors and potential substrates. These protease exosite scanning assays use protease exosites as bait to scan a cDNA library for possible interacting partners. Another early adaptation of yeast two-hybrid screening in protease-substrate discovery is Inactive-catalytic-domain capture (ICDC). This approach attempts to avoid the limitation of protease exosite scanning, which fails to account for any substrates that do not require exosites to for recognition before cleavage. The bait for these assays are immobilized catalytically inactive mutant protease domains that cannot cleave and release their substrates once bound. While useful in early degradomic studies, the limitations of adapted yeast two-hybrid screens have forced the field to move on to higher-throughput approaches for protease-substrate discovery. Their high rate of false positives and negatives, inability to recognize complex interactions, lack of biologically compartmentalization, and failure to account for post-translational modifications necessary for protein-protein interactions hamper their usefulness. Thus they have been largely replaced by proteomic methods as technology has improved.
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The Bundeswehr uses the Einpersonenpackung to provide two substantial meals to each soldier. The standard practice is to provide one hot cooked meal for the other meal whenever possible. A heater or oven is not included since an Esbit cooker is part of each soldier's personal equipment. Enough food items are contained within the Einpersonenpackung to sustain the soldier for 24 hours. Currently there are three menus; each includes two meals out of a selection of 19 meals, with several heavy-duty foil trays containing items such as lentils with sausages, Yugoslav Sausage, Goulash, beef burgers in tomato sauce, Italian pasta, or Tofu stir-fry. There are also three smaller foil "cans" of bread spreads such as cheese spread, liver-sausage, dried-meat sausage, or cheese spread with green peppers. The meal box also includes: thinly sliced rye bread (170 g), hard crackers (1100 kcal), a foil can of fruit salad, instant cream of wheat, instant fruit juice powder, instant coffee, instant tea, powdered cream, a chocolate bar, sugar, salt, gum, jam, water purifying tablets, two plastic bags, matches, paper towels, and a user guide. The Einpersonenpackung ration is supplied in two types, rations 1 to 5 are packaged in a grey cardboard box with the meals packaged in sealed heavy duty foil trays which may be heated by immersing in hot water. The trays are opened using a knife or other sharp implement. Rations 6 to 19 are packaged in a resealable carry pouch, which are either NATO Olive coloured, desert brown or transparent. The meals are packed in retort pouches.
=== Opposition to the Peace Preservation Act === In 1878, the Cape Parliament had passed the Peace Preservation Act, which allowed for the confiscation of the firearms of the African population in exchange for a monetary compensation. Sprigg decided that its implementation should extend to the Basuto, after witnessing 7,000 Basuto cavalrymen perform maneuvers during the course of Moorosi's uprising. This was announced during a pitso (formal assembly) attended by some 6,000 to 10,000 Basuto. Soon afterwards he also declared that the Quthing region would be confiscated by the Cape for white settlement. At the time almost half of all Basuto men owned a firearm. Many had worked in railway construction and the diamond mines in Griqualand West with the express purpose of purchasing modern breech-loading and smoothbore rifles. As a result, the Basuto became the best-armed tribe in southern Africa. For the Basuto gun confiscation was unacceptable, not only due to their high value, but also due to the necessity to defend their land and cattle in an environment where there was no guarantee of protection from the colonial authorities. For the Basuto, guns were a symbol of manhood, and to be disarmed was seen as being reduced to the status of a child. In April 1879, the Cape Colony doubled the hut tax in Basutoland to one £ per hut. In June 1880, Letsie I dispatched a three-man delegation to the Cape Parliament as it was deliberating the annexation of Quthing and the question of Basuto disarmament.
Sanger sequencing A method of DNA sequencing based on the in vitro replication of a DNA template sequence, during which fluorochrome-labeled, chain-terminating dideoxynucleotides are randomly incorporated in the elongating strand; the resulting fragments are then sorted by size with electrophoresis, and the particular fluorochrome terminating each of the size-sorted fragments is detected by laser chromatography, thus revealing the sequence of the original DNA template through the order of the fluorochrome labels as one reads from small-sized fragments to large-sized fragments. Though Sanger sequencing has been replaced in some contexts by next-generation methods, it remains widely used for its ability to produce relatively long sequence reads (500+ nucleotides) and its very low error rate.
Sources: en.wikipedia.org
== Professor of physiology == Best succeeded Macleod as professor of physiology at University of Toronto in 1929. During World War II he was influential in establishing a Canadian program for securing and using dried human blood serum. In his later years, he was an adviser to the Medical Research Committee of the United Nations World Health Organization.
== Career and research == He moved to the Department of Pharmaceutical Chemistry the University of California, San Francisco in the early 1970s. He founded the Molecular Design Institute at UCSF in 1993. He was awarded the UCSF medal in 2018.
Smooth muscle is involuntary and non-striated. It is divided into two subgroups: the single-unit (unitary) and multiunit smooth muscle. Within single-unit cells, the whole bundle or sheet contracts as a syncytium (i.e. a multinucleate mass of cytoplasm that is not separated into cells). Multiunit smooth muscle tissues innervate individual cells; as such, they allow for fine control and gradual responses, much like motor unit recruitment in skeletal muscle. Smooth muscle is found within the walls of blood vessels (such smooth muscle specifically being termed vascular smooth muscle) such as in the tunica media layer of the large (aorta) and small arteries, arterioles and veins. Smooth muscle is also found in lymphatic vessels, the urinary bladder, uterus (termed uterine smooth muscle), male and female reproductive tracts, the gastrointestinal tract, the respiratory tract, the arrector pili of skin, the ciliary muscle, and the iris of the eye. The structure and function is basically the same in smooth muscle cells in different organs, but the inducing stimuli differ substantially, in order to perform individual actions in the body at individual times. In addition, the glomeruli of the kidneys contain smooth muscle-like cells called mesangial cells.
Zearalenone (ZEN), also known as RAL and F-2 mycotoxin, is a potent estrogenic metabolite produced by some Fusarium and Gibberella species. Specifically, the Gibberella zeae, the fungal species where zearalenone was initially detected, in its asexual/anamorph stage is known as Fusarium graminearum. Several Fusarium species produce toxic substances of considerable concern to livestock and poultry producers, namely deoxynivalenol, T-2 toxin, HT-2 toxin, diacetoxyscirpenol (DAS) and zearalenone. Particularly, ZEN is produced by Fusarium graminearum, Fusarium culmorum, Fusarium cerealis, Fusarium equiseti, Fusarium verticillioides, and Fusarium incarnatum. Zearalenone is the primary toxin that binds to estrogen receptors, causing infertility, abortion or other breeding problems, especially in swine. Often, ZEN is detected together with deoxynivalenol in contaminated samples and its toxicity needs to be considered in combination with the presence of other toxins. Zearalenone is heat-stable and is found worldwide in a number of cereal crops, such as maize, barley, oats, wheat, rice, and sorghum. Its production increases when the climate is warm with air humidity at or above twenty percent. The environmental pH plays also a role in the toxin's production. When temperatures fall to 15 °C, alkaline soils still support ZEN production. At the preferred Fusarium temperature, which ranges between 25 °C and 30 °C, neutral pH results in the greatest toxin production.
Sources: en.wikipedia.org
Primary drying removes ice by sublimation under vacuum. Secondary drying removes water that is bound to the material, often by warming the product after most ice has left. Both stages occur below temperatures that would cause unwanted melting.
Sublimation requires the solvent to remain solid so vapor leaves without passing through a liquid phase. If the product melts, the porous structure can collapse and drying becomes uneven. Maintaining frozen conditions preserves the intended physical form.
No, freeze-drying is a dehydration method, not a sterilization step. It can reduce water activity and limit microbial growth during storage, but it does not reliably kill microbes or remove endotoxins. Sterility must come from separate validated processes.
Simple drying usually removes water by evaporation from a liquid or solid, often with heat. Lyophilization first freezes the material and then removes ice by sublimation under vacuum. This avoids prolonged exposure to liquid water and high temperatures.