A practical reference on Cake collapse: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2025-07-26. Anything still debated is marked as such rather than presented as settled.
Stability of a lyophilized product depends on its glass transition temperature, the temperature at which the amorphous cake transitions from a glassy to a rubbery state. Storage below this temperature minimizes molecular mobility and slows chemical degradation. If the storage temperature exceeds the glass transition temperature, the cake may collapse, shrink, or become sticky. Accelerated stability studies at elevated temperatures and humidity help predict shelf life, but they do not always reflect real-time behavior. Residual moisture content also plays a critical role in long-term stability.
Reconstitution involves adding a suitable diluent, often sterile water or a buffer, to the dried cake. Gentle swirling or inversion helps dissolve the material without creating excessive foam. The time required for complete dissolution can range from seconds to several minutes and depends on the cake structure and the diluent. Improper reconstitution, such as vigorous shaking or using the wrong diluent, can cause protein aggregation or loss of activity. After reconstitution, the product may have a limited shelf life and should be used according to its labeling.
Lyophilized products are typically hygroscopic and require protection from moisture during storage. Manufacturers seal them in glass vials, often under vacuum or an inert gas such as nitrogen. The container closure system, including the stopper and crimp seal, must prevent water vapor ingress. Storage temperature varies from controlled room temperature to refrigerated or frozen conditions, depending on the formulation. Humidity-controlled environments are essential because even brief exposure to ambient air can degrade the product.
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.
| Property | Value | Notes |
|---|---|---|
| Appearance | White to off-white porous cake | Color depends on formulation. |
| Typical storage temperature | 2–8 °C | Refrigerated for many biologics. |
| Residual moisture | <1% to 3% | Low moisture improves stability. |
| Container | Sealed glass vial | Often with rubber stopper and aluminum crimp. |
| Reconstitution time | Seconds to minutes | Varies with cake density and diluent. |
Quality control also examines cake structure, color, and reconstitution behavior. A collapsed or shrunken cake can indicate a thermal excursion during drying. Analytical methods such as X-ray diffraction, differential scanning calorimetry, and near-infrared spectroscopy can detect crystallinity or moisture distribution. Regulatory expectations focus on validated assays and lot-to-lot consistency. Questions remain about how well accelerated stability tests predict long-term behavior for every formulation. Visual inspection remains common but is subjective without trained reviewers and reference images.
After lyophilization, a product's quality depends on residual moisture, cake appearance, and reconstitution time. Residual moisture is often measured by Karl Fischer titration or thermogravimetric analysis. A low moisture content can slow chemical degradation, but overly dry cakes may be brittle or slow to dissolve. Stability studies track these attributes over months under defined temperature and humidity conditions. Batch records link these measurements to specific process runs and help identify trends before a product fails specification.
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.
Regulatory expectations for lyophilized products focus on consistent manufacture and documented stability. Batches are often monitored for moisture, appearance, potency, and sterility where applicable. Process parameters such as shelf temperature, chamber pressure, and drying time are recorded and controlled within validated ranges. Open questions remain about how best to predict long-term stability from short accelerated studies, especially for complex biologics. Variations in freezing rate and ice crystal size can produce differences that are not always visible but may affect performance.
After drying, a lyophilized product is usually sealed under vacuum or an inert gas to limit moisture uptake. Residual water content is measured because small changes can alter chemical stability and cake appearance. Storage temperature depends on the material; many biological products are kept at 2–8 °C, while some require −20 °C or colder. Exposure to ambient humidity during handling can cause the porous solid to absorb water and collapse. Container closures and stoppers are therefore selected for low moisture transmission and compatibility.
Quality control for lyophilized materials includes visual inspection of the cake, measurement of residual moisture, and tests for reconstitution time. An acceptable cake is typically uniform and may be slightly porous; shrinkage, meltback, or cracks can indicate process deviations. Analytical methods such as Karl Fischer titration, thermogravimetric analysis, and near-infrared spectroscopy quantify water content. Reconstitution time is recorded because a very slow or incomplete dissolution can signal collapse or aggregation. Stability studies compare samples stored under defined temperature and humidity conditions over months or years.
Formulation composition influences whether freeze-drying produces an intact cake or a collapsed mass. Excipients such as sugars and polymers can raise the collapse temperature and provide bulk during drying. The critical temperature for primary drying is often the collapse temperature or the glass transition temperature of the maximally concentrated phase. If the product temperature exceeds this threshold, the frozen matrix may soften and lose structure. Established practice therefore links shelf temperature and chamber pressure to the formulation's thermal properties.
The physics of freeze-drying couples heat transfer, mass transfer, and phase change. Heat supplied through the shelf must reach the sublimation front without melting the ice or degrading the product. Water vapor then travels through the already dried layer and leaves the chamber, where low pressure and cold traps keep it from returning. The dried layer acts as a resistance to vapor flow, so drying rate changes as the front recedes. Open questions remain about how pore structure and formulation heterogeneity affect drying uniformity at larger scales.
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and concentrates dissolved solids. Primary drying then lowers chamber pressure so ice changes directly into vapor without passing through a liquid phase. Secondary drying raises the shelf temperature to remove bound water that remains after ice sublimation. The result is a dry, porous structure that can be reconstituted later.
==== MeSH D06.472.610 – pancreatic hormones ==== MeSH D06.472.610.469 – glucagon precursors MeSH D06.472.610.469.500 – glucagon MeSH D06.472.610.575 – insulin MeSH D06.472.610.575.408 – insulin, isophane MeSH D06.472.610.575.532 – insulin, long-acting MeSH D06.472.610.575.788 – proinsulin MeSH D06.472.610.575.788.250 – c-peptide MeSH D06.472.610.700 – pancreatic polypeptide MeSH D06.472.610.780 – somatostatin
== Interactions == Vardenafil should not be used by people taking nitrate medications, because combining them with vardenafil might provoke potentially life-threatening hypotension (low blood pressure). Further, vardenafil causes lengthening of the QT interval. Therefore, it should not be taken by people taking other medications that affect the QT interval (such as amiodarone).
As with any sterilisation method, a very small proportion of germs may survive the process, and cause a fraction of the irradiated products to spoil anyway. The risk comes from the false sense of security. As mentioned above, the treatment only preserves the freshness of the product at the moment it reaches the factory. If it has already lost some of its qualities, this will not be restored, and may even be hidden by the packaging. While the purpose of the irradiation is to degrade the DNA/RNA of contaminating germs, a small proportion of the nutrient load is also degraded in the process. In particular, vitamins, whole proteins and aromatic molecules. The irradiation creates highly reactive radicals, which would cause problems if the food is consumed immediately after being irradiated.
Heat or ionizing irradiation can be used to kill the bacteria that cause decomposition. Heat is applied by cooking, blanching or microwave heating in a manner that pasteurizes or sterilizes fish products. Cooking or pasteurizing does not completely inactivate microorganisms and may need to be followed with refrigeration to preserve fish products and increase their shelf life. Sterilised products are stable at ambient temperatures up to 40 °C, but to ensure they remain sterilized they need packaging in metal cans or retortable pouches before the heat treatment.
===== MeSH D08.811.277.040 – acid anhydride hydrolases (EC 3.6) ===== MeSH D08.811.277.040.025 – adenosinetriphosphatase MeSH D08.811.277.040.025.095 – ca(2+) mg(2+)-atpase MeSH D08.811.277.040.025.125 – ca(2+)-transporting atpase MeSH D08.811.277.040.025.150 – dynein atpase MeSH D08.811.277.040.025.237 – muts dna mismatch-binding protein MeSH D08.811.277.040.025.281 – muts homolog 2 protein MeSH D08.811.277.040.025.303 – n-ethylmaleimide-sensitive proteins MeSH D08.811.277.040.025.325 – proton-translocating atpases MeSH D08.811.277.040.025.325.249 – bacterial proton-translocating atpases MeSH D08.811.277.040.025.325.500 – chloroplast proton-translocating atpases MeSH D08.811.277.040.025.325.625 – h(+)-k(+)-exchanging atpase MeSH D08.811.277.040.025.325.750 – mitochondrial proton-translocating atpases MeSH D08.811.277.040.025.325.875 – vacuolar proton-translocating atpases MeSH D08.811.277.040.025.450 – kinesin MeSH D08.811.277.040.025.525 – myosins MeSH D08.811.277.040.025.525.500 – myosin type i MeSH D08.811.277.040.025.525.750 – myosin type ii MeSH D08.811.277.040.025.525.750.124 – cardiac myosins MeSH D08.811.277.040.025.525.750.124.249 – atrial myosins MeSH D08.811.277.040.025.525.750.124.500 – ventricular myosins MeSH D08.811.277.040.025.525.750.374 – nonmuscle myosin type iia MeSH D08.811.277.040.025.525.750.500 – nonmuscle myosin type iib MeSH D08.811.277.040.025.525.750.750 – skeletal muscle myosins MeSH D08.811.277.040.025.525.750.875 – smooth muscle myosins MeSH D08.811.277.040.025.525.812 – myosin type iii MeSH D08.811.277.040.025.525.843 – myosin type iv MeSH D08.811.277.040.025.525.875 – myosin type v MeSH D08.811.277.040.025.600 – na(+)-k(+)-exchanging atpase MeSH D08.811.277.040.050 – apyrase MeSH D08.811.277.040.330 – gtp phosphohydrolases MeSH D08.811.277.040.330.200 – dynamins MeSH D08.811.277.040.330.200.100 – dynamin i MeSH D08.811.277.040.330.200.200 – dynamin ii MeSH D08.811.277.040.330.200.300 – dynamin iii MeSH D08.811.277.040.330.300 – gtp-binding proteins MeSH D08.811.277.040.330.300.100 – gtp phosphohydrolase-linked elongation factors MeSH D08.811.277.040.330.300.100.200 – peptide elongation factor g MeSH D08.811.277.040.330.300.100.700 – peptide elongation factor tu MeSH D08.811.277.040.330.300.100.800 – peptide elongation factor 1 MeSH D08.811.277.040.330.300.100.850 – peptide elongation factor 2 MeSH D08.811.277.040.330.300.200 – heterotrimeric gtp-binding proteins MeSH D08.811.277.040.330.300.200.100 – gtp-binding protein alpha subunits MeSH D08.811.277.040.330.300.200.100.100 – gtp-binding protein alpha subunits, g12-g13 MeSH D08.811.277.040.330.300.200.100.200 – gtp-binding protein alpha subunits, gi-go MeSH D08.811.277.040.330.300.200.100.200.500 – gtp-binding protein alpha subunit, gi2 MeSH D08.811.277.040.330.300.200.100.300 – gtp-binding protein alpha subunits, gq-g11 MeSH D08.811.277.040.330.300.200.100.400 – gtp-binding protein alpha subunits, gs MeSH D08.811.277.040.330.300.200.800 – transducin MeSH D08.811.277.040.330.300.400 – monomeric gtp-binding proteins MeSH D08.811.277.040.330.300.400.100 – adp-ribosylation factors MeSH D08.811.277.040.330.300.400.100.100 – ADP-ribosylation factor 1 MeSH D08.811.277.040.330.300.400.400 – rab gtp-binding proteins MeSH D08.811.277.040.330.300.400.400.025 – rab1 gtp-binding proteins MeSH D08.811.277.040.330.300.400.400.050 – rab2 gtp-binding protein MeSH D08.811.277.040.330.300.400.400.100 – rab3 gtp-binding proteins MeSH D08.811.277.040.330.300.400.400.100.500 – rab3a gtp-binding protein MeSH D08.811.277.040.330.300.400.400.150 – rab4 gtp-binding proteins MeSH D08.811.277.040.330.300.400.400.200 – rab5 gtp-binding proteins MeSH D08.811.277.040.330.300.400.450 – ral gtp-binding proteins MeSH D08.811.277.040.330.300.400.462 – ran gtp-binding protein MeSH D08.811.277.040.330.300.400.475 – rap gtp-binding proteins MeSH D08.811.277.040.330.300.400.475.100 – rap1 gtp-binding proteins MeSH D08.811.277.040.330.300.400.500 – ras proteins MeSH D08.811.277.040.330.300.400.500.300 – oncogene protein p21(ras) MeSH D08.811.277.040.330.300.400.500.600 – proto-oncogene proteins p21(ras) MeSH D08.811.277.040.330.300.400.700 – rho gtp-binding proteins MeSH D08.811.277.040.330.300.400.700.050 – cdc42 gtp-binding protein MeSH D08.811.277.040.330.300.400.700.060 – cdc42 gtp-binding protein, saccharomyces cerevisiae MeSH D08.811.277.040.330.300.400.700.100 – rac gtp-binding proteins MeSH D08.811.277.040.330.300.400.700.100.500 – rac1 gtp-binding protein MeSH D08.811.277.040.330.300.400.700.200 – rhoa gtp-binding protein MeSH D08.811.277.040.330.300.400.700.300 – rhob gtp-binding protein MeSH D08.811.277.040.465 – nucleoside-triphosphatase MeSH D08.811.277.040.600 – pyrophosphatases MeSH D08.811.277.040.600.399 – inorganic pyrophosphatase MeSH D08.811.277.040.600.800 – thiamine pyrophosphatase MeSH D08.811.277.040.850 – thiamin-triphosphatase
Sources: en.wikipedia.org
However, as Liebling began to make his first attempts at recovery, the filmmakers started to see potential in his journey. Shaping Last Days Here into a coherent narrative proved to be a challenge. Liebling's personality was more erratic than the documentary ultimately portrayed. "Many times we had to finesse the rapid shifts in Bobby's life so the viewer wouldn't be left confused. Over the three years we were shooting, we saw the many different faces of Bobby Liebling. The delusional crack-smoking hustler, the arrogant '70s rock star, and the really cool loveable uncle. When boiling the footage down to 90 minutes, we really wanted to exemplify a balance of those personalities. That balance is sometimes tough to maintain," stated Fenton.
This inhibition can lead to a depletion of dopamine and norepinepherine in the brain due to the lack of the precursor L-DOPA (L-3,4-dyhydroxyphenylalanine) which is synthesized by tyrosine hydroxylase. This drug is rarely used and can cause depression, but it is useful in treating pheochromocytoma and also resistant hypertension. Older examples of inhibitors mentioned in the literature include oudenone and aquayamycin.
Integrative, multi-locus studies have prompted major revisions of several lichen families and genera. Two examples illustrate the impact of these studies: the re-circumscription of the family Graphidaceae and of the family Ramalinaceae. Graphidaceae—the script lichen family—contains more than 2,000 mostly tropical species. Traditional taxonomy centred on fruiting body shape and a few microscopic characters. A five-locus phylogeny (Rivas-Plata and Lumbsch 2011) showed that many characters had evolved convergently. Slit-like versus rounded discs arose repeatedly, so genera built on those traits mixed unrelated species. Molecular results led to a wholesale recircumscription: several traditional genera were divided and new ones erected to reflect monophyletic clades. For instance, the broad Graphis was split into several smaller, genetically and chemically homogeneous genera. This process was facilitated by projects such as Ticolichen (a tropical lichen inventory project) which combined fieldwork, morphology, chemistry, and DNA sequencing to tackle these revisions. The outcome is a more natural scheme: genera now align with monophyletic clades, even when outwardly dissimilar species must be grouped together. The revision greatly increased recognized genera and species, exposing hidden diversity in tropical crustose lichens. Another major revision, in this case of a mostly temperate/tropical group, was carried out by Kistenich and colleagues (2018) on the family Ramalinaceae. The family had about 40 genera of uncertain affinity, several delimited by only one or two traits.
Hydrophilic/cytosolic – are soluble in water and are localized at the cytosol, including cAMP, cGMP, IP3, Ca2+, cADPR and S1P. Their main targets are protein kinases as PKA and PKG, being then involved in phosphorylation mediated responses. Hydrophobic/membrane-associated – are insoluble in water and membrane-associated, being localized at intermembrane spaces, where they can bind to membrane-associated effector proteins. Examples: PIP3, DAG, phosphatidic acid, arachidonic acid and ceramide. They are involved in regulation of kinases and phosphatases, G protein associated factors and transcriptional factors. Gaseous – can be widespread through cell membrane and cytosol, including nitric oxide and carbon monoxide. Both of them can activate cGMP and, besides of being capable of mediating independent activities, they also can operate in a coordinated mode.
==== Pleistocene/Holocene boundary in Two Creeks Fossil Forest ==== The Pleistocene is a geological epoch that began about 2.6 million years ago. The Holocene, the current geological epoch, begins about 11,700 years ago when the Pleistocene ends. Establishing the date of this boundary − which is defined by sharp climatic warming − as accurately as possible has been a goal of geologists for much of the 20th century. At Two Creeks, in Wisconsin, a fossil forest was discovered (Two Creeks Buried Forest State Natural Area), and subsequent research determined that the destruction of the forest was caused by the Valders ice readvance, the last southward movement of ice before the end of the Pleistocene in that area. Before the advent of radiocarbon dating, the fossilized trees had been dated by correlating sequences of annually deposited layers of sediment at Two Creeks with sequences in Scandinavia. This led to estimates that the trees were between 24,000 and 19,000 years old, and hence this was taken to be the date of the last advance of the Wisconsin glaciation before its final retreat marked the end of the Pleistocene in North America. In 1952 Libby published radiocarbon dates for several samples from the Two Creeks site and two similar sites nearby; the dates were averaged to 11,404 BP with a standard error of 350 years. This result was uncalibrated, as the need for calibration of radiocarbon ages was not yet understood. Further results over the next decade supported an average date of 11,350 BP, with the results thought to be the most accurate averaging 11,600 BP.
Sources: en.wikipedia.org
Insulin aspart, which was approved in 2000 and is marketed under the name Novolog among others, has effects comparable to those of insulin lispro, but has a lesser risk of nocturnal hypoglycemia. It works by replacing a proline with an aspartic acid at the B28 position. Insulin glulisine has nearly identical properties to the other two short-acting analogues, but differs in the fact that the amino acid asparagine at position B3 is replaced by lysine and the lysine in position B29 is replaced by glutamic acid. It was approved in 2004 and is sold under the name Apidra. These short-acting insulin analogues play a crucial role in modern diabetes management, as their fast onset and shorter duration of action allow for more precise postprandial glucose control. By closely mimicking endogenous insulin secretion, these analogues enhance glycemic stability, reduce post-meal blood sugar spikes, and minimize the risk of hypoglycemic events. Their pharmacokinetic properties make them particularly beneficial for individuals requiring flexible meal timing and those using intensive insulin therapy.
These plans had been made some time ago." Russian military intelligence source alleged that the United States knew the date when the war in South Ossetia would begin because the United States military delegation cancelled the visit to Russia, which was scheduled on 10-14 August, on August 1 and cited the absence of the Russian permit for the flight. In late August 2008, Batu Kutelia, the deputy defence minister told the Financial Times that the decision to take Tskhinvali was made in spite of the fact that Georgia did not have enough anti-tank and air defences because "At some point there was no choice." He also said that Georgian authorities and military did not expect Russia to use a large-scale force against Georgia. In August 2008, Steven Pifer, former Ambassador to Ukraine, said that there were signs that the Russian invasion had been prepared in advance, with Russia waiting for Georgia to fall in a trap and using the Georgian response as a pretext. Secretary of State for Foreign and Commonwealth Affairs David Miliband visited Ukraine in late August and told Ukrainians "not to provide any pretext" for Russia. He said, "The Russians have used those pretexts in the Georgian case and it's important to not repeat that." Georgian reintegration minister Temur Iakobashvili said, "The pilots we captured reported that they were mobilized days before Aug. 8.
=== Bone repair === Bone has a unique and well-documented natural healing process that normally is sufficient to repair fractures and other common injuries. Misaligned breaks due to severe trauma, as well as treatments like tumor resections of bone cancer, are prone to improper healing if left to the natural process alone. Scaffolds composed of natural and artificial components are seeded with mesenchymal stem cells and placed in the defect. Within four weeks of placing the scaffold, newly formed bone begins to integrate with the old bone and within 32 weeks, full union is achieved. Further studies are necessary to fully characterize the use of cell-based therapeutics for treatment of bone fractures. Stem cells have been used to treat degenerative bone diseases in dogs. The normally recommended treatment for dogs that have Legg–Calve–Perthes disease is to remove the head of the femur after the degeneration has progressed. Recently, mesenchymal stem cells have been injected directly in to the head of the femur, with success not only in bone regeneration, but also in pain reduction.
Hot cathode gauges are accurate from 10−3 torr to 10−10 torr. The principle behind cold cathode version is the same, except that electrons are produced in a discharge created by a high voltage electrical discharge. Cold cathode gauges are accurate from 10−2 torr to 10−9 torr. Ionization gauge calibration is very sensitive to construction geometry, chemical composition of gases being measured, corrosion and surface deposits. Their calibration can be invalidated by activation at atmospheric pressure or low vacuum. The composition of gases at high vacuums will usually be unpredictable, so a mass spectrometer must be used in conjunction with the ionization gauge for accurate measurement.
5 December Junior doctors in England will stage further strike action after rejecting the latest pay offer, the British Medical Association confirms, with a three-day strike scheduled to begin on 20 December and a six-day strike scheduled to begin on 3 January 2024. The Scottish Prison Service issues new guidelines on transgender prisoners. Trans women who have hurt or threatened women or girls will not be sent to a female prison unless there are "exceptional" circumstances. Jesse Darling is announced as the winner of the 2023 Turner Prize. 6 December Boris Johnson, who served as prime minister from 2019 to 2022, appears before the COVID-19 inquiry and is questioned by Hugo Keith, counsel to the inquiry. He apologises for the "pain and the loss and the suffering" people experienced during the pandemic. His comments are interrupted by protesters, who are ordered to leave the inquiry room. Robert Jenrick resigns as immigration minister after the government publishes an emergency Rwanda bill. 7 December Figures released by Halifax Bank indicate house prices in the UK rose by 0.5% in November 2023. Culture Secretary Lucy Frazer confirms the TV licence fee will increase by £10.50 from £159 to £169.50 from 1 April 2024. Serial killer Steve Wright is arrested for the September 1999 murder of Victoria Hall. 8 December A letter to MPs from Sir Matthew Rycroft, the Permanent Under-Secretary of State of the Home Office, says that £240m has been paid so far to Rwanda for the Rwanda asylum plan, with a further £50m to be paid in 2024.
Sources: en.wikipedia.org
Lyophilized products should be stored in airtight containers, protected from moisture and light, at the temperature specified by the manufacturer. Many require refrigeration at 2–8 °C, while some need frozen storage. Always check the product label for specific conditions.
Moisture can cause the porous cake to collapse, increase molecular mobility, and accelerate chemical degradation. It may also promote microbial growth if the product lacks preservatives. Proper sealing and handling are essential to maintain stability.
Some formulations contain labile biological molecules that degrade even in the dry state at higher temperatures. Others have a low glass transition temperature, meaning the cake can soften or collapse at room temperature. Cold storage reduces molecular motion and slows degradation.
The main change is sublimation, in which ice becomes water vapor without melting into liquid water. This occurs when the chamber pressure is held below the vapor pressure of ice while mild heat is supplied. The result is a dry, porous solid that retains much of its original shape.