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OfflineGaNjAShRooM
===SPUN===

Registered: 02/22/02
Posts: 2,954
Loc: Southern United States
Last seen: 8 years, 1 month
drying problems-freeze drying?
    #592647 - 03/29/02 10:14 AM (15 years, 4 months ago)

i have this cheap ass dehydrator-every time i dry my shrooms,they turn to shit-they look horrible-
when i used to buy shrooms from my old dealer where i used to live,they never looked liked mine do now-
he always said they were freeszer dried-
ands thats what they looked like-
they looked like they had been picked and froze in perfect condition-they didnt fall apart as bad as mine do-
so my question comes to this-
what did he mean by freeze dried?
how did they get their shrooms like that?
desiccant?
thanks all,
Lee


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Offlinehispeed67
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Loc: Florida
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Re: drying problems-freeze drying? [Re: GaNjAShRooM]
    #592660 - 03/29/02 10:44 AM (15 years, 4 months ago)

I would like to know this also. I stopped using my dehydrator (got too hot) and use fan drying and dry-rite now. How does one do freeze drying???


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InvisibleWakingUpLate
addict
Registered: 12/29/01
Posts: 559
Loc: Born on a mountain, Raise...
Re: drying problems-freeze drying? [Re: hispeed67]
    #592706 - 03/29/02 11:51 AM (15 years, 4 months ago)

If you guys put fresh shrooms in the freezer, you'll be sorry.
When it thaws it will be a purple slimey mess. It's possible
that your dealer lied about how they were dried, or didn't
know. Kinda like misleading someone about exactly where
that 7 lb. bass was caught.
Looks don't mean much, but Ihave a feeling that drying under
a vaccume may produce pretty results but I haven't taken the
time to finish my vaccume chamber yet.
I hope you haven't put any in the freezer yet. :peace: 

Free Spore Ring

 


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cannot settle the unrest of those who follow.
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OfflineSeussA
Error: divide byzero

Folding@home Statistics
Registered: 04/27/01
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Re: drying problems-freeze drying? [Re: hispeed67]
    #592715 - 03/29/02 12:03 PM (15 years, 4 months ago)

You need a freeze dryer to freeze dry something. They work by using a vacuum to lower the pressure in the drying chamber and by lowering the temperature at the same time. As the water begins to freeze, it sublimes (turns from solid into gas skipping the liquid phase) because of the low pressure.

In a normal freezer, the water expands as it turns into ice. This expansion causes the cells inside the fruitbody to grind together and break apart. The ice also doesn't go anywhere, so when the fruit thaws you end up with water again. The fruit also turns into a slimy mess when it thaws because all the cell structure has been destroyed by the freezing action.

In the freeze dryer, the ice turns into a gas as it forms so the cell bodies are not destroyed. The vacuum removes the excess water vapor. When the cycle is done, you are left with very dry and well preserved fruit that is water free.


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InvisibleWakingUpLate
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Re: drying problems-freeze drying? [Re: Seuss]
    #592739 - 03/29/02 12:44 PM (15 years, 4 months ago)

Damn, That's good to know! So here's my question, how much
vaccum does it use? And, if you can pull enough to drop the
boiling point to below room temperature, do you really need it
to be freezing? I know that the expantion of the water in the
cell during freezing causes them to rupture. But does the
water boiling out quickly damage it the same way? And does
it matter, since it's dry. I'm convinced that some potency
could be saved because of less time for the goodies to be
exposed to oxygen.
I'd really like to hear your opinion on this. Thanks
:peace:

Free Spore Ring
 


--------------------
The rest of those, who have gone before us,
cannot settle the unrest of those who follow.
(Finding Forrester)


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OfflineGaNjAShRooM
===SPUN===

Registered: 02/22/02
Posts: 2,954
Loc: Southern United States
Last seen: 8 years, 1 month
Re: drying problems-freeze drying? [Re: WakingUpLate]
    #592745 - 03/29/02 12:51 PM (15 years, 4 months ago)

looks like this was a good post to start-does anyone have a plan for a set-up using freeze drying or vacum drying-id love to try and make a set up like that :smile: 


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OfflineSeussA
Error: divide byzero

Folding@home Statistics
Registered: 04/27/01
Posts: 23,480
Loc: Caribbean
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Re: drying problems-freeze drying? [Re: WakingUpLate]
    #592746 - 03/29/02 12:53 PM (15 years, 4 months ago)



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InvisibleWakingUpLate
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Re: drying problems-freeze drying? [Re: Seuss]
    #592770 - 03/29/02 01:18 PM (15 years, 4 months ago)

Ok, I downloaded it, and tried to open it. It said "Formatting 100%...please wait"
and then froze my computer up.
Come on man, that's not your opinion.
I work on refrigeration so I know this: One drop of water can
render and air conditioner, heat pump, or refrigeration unit useless.
If even a little moisture get into a system it must be vaccumed.
Pulling absolute vaccume (30 inches of water column) can boil
a drop of water out even if it's at the bottom of the compressor
under a foot of oil. A real vaccum pump costs about $175
But I have seen one built from a compressor out of an old
refrigerator. I haven't tried that, but I've seen it work.
I still don't quite grasp freeze drying. Freezing and boiling are
at opposite ends of the spectrum. Pressure changes the boiling
point. Does it also change the freezing point. Sorry if these
are stupid questions.
:peace:

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--------------------
The rest of those, who have gone before us,
cannot settle the unrest of those who follow.
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OfflineAnnoA
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Re: drying problems-freeze drying? [Re: WakingUpLate]
    #592800 - 03/29/02 02:05 PM (15 years, 4 months ago)

Works for me.

Here a the text version of this document, without pictures off course.A Guide ToFreeze Drying for the Laboratory

An Industry Service Publication

Foreword

This booklet has been developed to serve as a basicguide to the freeze drying process. The information presented is generic in nature and is the result ofresearch and experience by Labconco personnel and users of freeze drying equipment. It is our intention toprovide a non-biased review of preparation techniques and freeze drying methods. The purpose of this booklet isto help you make an informed choice of equipment for your laboratory applications.

Our Method

We begin our discussion of freeze drying for thelaboratory by examining the three steps in the process: prefreezing, primary drying and secondary drying. Next,we examine a typical freeze drying cycle and the methods available to facilitate the freeze drying process usingequipment designed for use by laboratories. Finally, suggestions to optimize successful results are discussed,including determination of end point, contamination, backfilling of dried samples and product stability. A glossary of terms used throughout this booklet to explain the freeze drying process follows the text, alongwith a bibliography.

Introduction

Freeze drying has been used in a number ofapplications for many years, most commonly in the food and pharmaceutical industries. There are, however, manyother uses for the process including the stabilization of living materials such as microbial cultures, preservationof whole animal specimens for museum display, restoration of books and other items damaged by water,and the concentration and recovery of reaction products.

Specialized equipment is required to create theconditions conducive to the freeze drying process. This equipment is currently available and can accommodatefreeze drying of materials from laboratory scale projects to industrial production.Freeze drying involves the removal of water or other solvent from a frozen product by a process calledsublimation. Sublimation occurs when a frozen liquid goes directly to the gaseous state without passingthrough the liquid phase. In contrast, drying at ambient temperatures from the liquid phase usually results inchanges in the product, and may be suitable only for some materials. However, in freeze drying, the materialdoes not go through the liquid phase, and it allows the preparation of a stable product that is easy to use andaesthetic in appearance.

The advantages of freeze drying are obvious. Properlyfreeze dried products do not need refrigeration, and can be stored at ambient temperatures. Because the costof the specialized equipment required for freeze drying can be substantial, the process may appear to be anexpensive undertaking. However, savings realized by stabilizing an otherwise unstable product at ambienttemperatures, thus eliminating the need for refrigeration, more than compensate for the investmentin freeze drying equipment.

Principles of Freeze Drying

The freeze drying process consists of three stages:prefreezing, primary drying, and secondary drying. Prefreezing: Since freeze drying is a change in statefrom the solid phase to the gaseous phase, material to be freeze dried must first be adequately prefrozen. Themethod of prefreezing and the final temperature of the frozen product can affect the ability to successfully freezedry the material.

Rapid cooling results in small ice crystals, useful inpreserving structures to be examined microscopically, but resulting in a product that is more difficult to freeze dry. Slower cooling results in larger ice crystals and less restrictive channels in the matrix during thedrying process.

Products freeze in two ways, depending on themakeup of the product. The majority of products that are subjected to freeze drying consist primarily of water, thesolvent, and the materials dissolved or suspended in the water, the solute. Most samples that are to be freeze driedare eutectics which are a mixture of substances that freeze at lower temperatures than the surrounding water.When the aqueous suspension is cooled, changes occur in the solute concentrations of the product matrix. Andas cooling proceeds, the water is separated from the solutes as it changes to ice, creating more concentratedareas of solute. These pockets of concentrated materials have a lower freezing temperature than the water.Although a product may appear to be frozen because of all the ice present, in actuality it is not completely frozenuntil all of the solute in the suspension is frozen. The mixture of various concentration of solutes with thesolvent constitutes the eutectic of the suspension. Only when all of the eutectic mixture is frozen is thesuspension properly frozen. This is called the eutectic temperature.It is very important in freeze drying to prefreeze the product to below the eutectic temperature beforebeginning the freeze drying process. Small pockets of unfrozen material remaining in the product expand and compromise the structural stability of the freeze dried product.The second type of frozen product is a suspension that undergoes glass formation during the freezing process.Instead of forming eutectics, the entire suspension becomes increasingly viscous as the temperature islowered. Finally the product freezes at the glass transition point forming a vitreous solid. This type ofproduct is extremely difficult to freeze dry.

Primary drying: Several factors can affect the abilityto freeze dry a frozen suspension. While these factors can be discussed independently, it must be remembered thatthey interact in a dynamic system, and it is this delicate balance between these factors that results in a properlyfreeze dried product.

After prefreezing the product, conditions must beestablished in which ice can be removed from the frozen product via sublimation, resulting in a dry, structurallyintact product. This requires very careful control of the two parameters, temperature and pressure, involved inthe freeze drying system. The rate of sublimation of ice from a frozen product depends upon the difference in vapor pressure of the product compared to the vaporpressure of the ice collector. Molecules migrate from the higher pressure sample to a lower pressure area. Sincevapor pressure is related to temperature, it is necessary that the product temperature is warmer than the coldtrap (ice collector) temperature. It is extremely important that the temperature at which a product isfreeze dried is balanced between the temperature that maintains the frozen integrity of the product and thetemperature that maximizes the vapor pressure of the product. This balance is key to optimum drying. Thetypical phase diagram shown in Figure 1 illustrates this point. Most products are frozen well below their eutecticor glass transition point (Point A), and then the temperature is raised to just below this criticaltemperature (Point B) and they are subjected to a reduced pressure. At this point the freeze drying processis started.

Figure 1

A typical phase diagram. Some products such as aqueous sucrose solutions canundergo structural changes during the drying process resulting in a phenomenon known as collapse. Althoughthe product is frozen below its eutectic temperature, warming during the freeze drying process can affect thestructure of the frozen matrix at the boundary of the drying front. This results in a collapse of the structuralmatrix. To prevent collapse of products containing a vacuum pump is essential to evacuate the environment around the product to be freeze dried.


sucrose, the product temperature must remain below acritical collapse temperature during primary drying. The collapse temperature for sucrose is -32o C. No matter what type of freeze drying system is used, conditions must be created to encourage the free flow ofwater molecules from the product. Therefore, a vacuum pump is an essential component of a freeze dryingsystem, and is used to lower the pressure of the environment around the product (to Point C). The otheressential component is a collecting system, which is a cold trap used to collect the moisture that leaves thefrozen product. The collector condenses out all condensable gases, i.e; the water molecules, and thevacuum pump removes all non-condensable gases.

The collecting system acts as a cold trap to collectmoisture leaving the frozen product.

It is important to understand that the vapor pressureof the product forces the sublimation of the water vapor molecules from the frozen product matrix to thecollector. The molecules have a natural affinity to move toward the collector because its vapor pressure is lowerthan that of the product. Therefore, the collector temperature (Point D) must be significantly lower thanthe product temperature. As can be noted in Table 1, raising the product temperature has more effect on the vapor pressure differential than lowering the collector temperature. Table 1

Vapor Pressure/Temperature Relationships

A third component essential in a freeze drying systemis energy. Energy is supplied in the form of heat. Almost ten times as much energy is required to sublime a gramof water from the frozen to the gaseous state as is required to freeze a gram of water. Therefore, with allother conditions being adequate, heat must be applied to the product to encourage the removal of water in theform of vapor from the frozen product. The heat must be very carefully controlled, as applying more heat than theevaporative cooling in the system can remove warms the product above its eutectic or collapse temperature.Heat can be applied by several means. One method is to apply heat directly through a thermal conductor shelfsuch as is used in tray drying. Another method is to use ambient heat as in manifold drying. Secondary drying: After primary freeze drying is complete, and all ice has sublimed, bound moisture isstill present in the product. The product appears dry, but the residual moisture content may be as high as 7-8%.Continued drying is necessary at the warmer temperature to reduce the residual moisture content tooptimum values. This process is called isothermal desorption as the bound water is desorbed from the product.

Secondary drying is normally continued at a producttemperature higher than ambient but compatible with the sensitivity of the product. All other conditions, suchas pressure and collector temperature, remain the same. Because the process is desorptive, the vacuum should beas low as possible (no elevated pressure) and the collector temperature as cold as can be attained. Secondary dryingis usually carried out for approximately 1/3 to 1/2 the time required for primary drying.

How Freeze Drying Works

Refer to the phase diagram (Figure 1) and a typicalsublimation cycle (Figure 2). The product is first cooled to below its eutectic temperature (Point A). The collectoris cooled to a temperature approximately 20o C cooler than the product temperature, generally around -50 to -80o C. The product should be freeze dried at a temperature slightly lower than its eutectic or collapsetemperature (Point B) since the colder the product, the longer the time required to complete primary drying, andthe colder the collector temperature required to adequately freeze dry the product.After the product is adequately frozen and the collector temperature achieved, the system is evacuatedto at least 50 microns of mercury (.066 mBar) using a vacuum pump (Point C). At this point, primary drying ofthe product begins and continues until the entire frozen matrix appears dry. Heat input to the product may beachieved by several means such as increasing the shelf temperature in the case of tray drying, or using a liquidbath for manifold drying. While the collector and vacuum pump create the conditions for allowing sublimation tooccur, heat input is really the driving force behind the whole process.Heat input to the product must be very carefully controlled especially during the early stages of drying.

Vapor Pressure (mBar) Temperature (oC)

6.104 0 2.599 -10 1.034 -20 0.381 -30 0.129 -40 0.036 -50

0.011 -60 0.0025 -70 0.0005 -80

Figure 2

Typical Sublimation Cycle found in system utilizing Tray Dryer with shelves. The configuration of the product container and thevolume of the contained product can affect the amount of heat that can be applied. For small volumes of material,evaporative cooling compensates for high levels of heat and drying is accelerated.The volume and configuration of the suspension to be freeze dried often determines how the material is freezedried. For example, the greater the ratio of the surface area to the volume of the suspension, the faster dryingoccurs. This is because a greater area for the water molecules to leave the product exists compared to thedistance they have to travel to reach the surface of the frozen matrix. Drying occurs from the top of the productand initially the removal of water molecules is efficient. However, as the drying front moves down through the Figure 3

Ambient room temperature provides heat to encourage removal of water vapor from frozen samples when manifold drying.

product, drying becomes more and more difficult. Thewater molecules must now travel through the dried portions of the product which impedes their progress. Asthe drying front moves farther and farther down the matrix, the application of heat to the product becomesmore important (Figure 3).

Shell freezing as a method of prefreezing the productcan increase the surface area to volume ratio by spreading out the frozen product inside the vessel(Figure 4). Shell freezing is accomplished by rotating the vessel in a low temperature bath causing the product tofreeze in a thin layer on the inside surface of the vessel. The thickness of the frozen suspension depends on thevolume of the product in comparison to the size of the vessel. Shell freezing is primarily used in conjunctionwith manifold drying.

The vacuum system is very important during freezedrying because the pressure must be maintained as low as possible to ensure adequate water vapor flow from theproduct to the collector. A pressure gauge (commonly called a vacuum gauge) is used to monitor the pressurein the system during the drying process. Pressure can be expressed in several different units which are comparedin Table 2. Some gauges measure condensable gases, while others do not. Those gauges that do not measurethe condensable gases give an indication of the total pressure in the system. Gauges that do sense thecondensable gases indicate a change in pressure during drying. These sensors can be used as an indication of the rate of drying, as well as the endpoint of the drying process. Figure 4

Shell freezing can increase the surface area to volume ratio by spreading out the frozen product inside the vessel. Table 2

Freeze Drying Methods

Three methods of freeze drying are commonly used:(1) manifold drying, (2) batch drying, and (3) bulk drying. Each method has a specific purpose, and themethod used depends on the product and the final configuration desired.Manifold Method. In the manifold method, flasks, ampules or vials are individually attached to the ports ofa manifold or drying chamber. The product is either frozen in a freezer, by direct submersion in a lowtemperature bath, or by shell freezing, depending on the nature of the product and the volume to be freeze dried.The prefrozen product is quickly attached to the drying chamber or manifold to prevent warming. The vacuummust be created in the product container quickly, and the operator relies on evaporative cooling to maintain thelow temperature of the product. This procedure can only be used for relatively small volumes and products withhigh eutectic and collapse temperatures.

Manifold drying has several advantages over batch traydrying. Since the vessels are attached to the manifold individually, each vial or flask has a direct path to thecollector. This removes some of the competition for molecular space created in a batch system, and is mostideally realized in a cylindrical drying chamber where the distance from the collector to each product vessel is thesame. In a "tee" manifold, the water molecules leaving the product in vessels farthest from the collectorexperience some traffic congestion as they travel past the ports of other vessels.

In the manifold drying method, flasks are individually attached to the ports of a drying chamber.

Heat input can be affected by simply exposing thevessels to ambient temperature or via a circulating bath. For some products, where precise temperature control isrequired, manifold drying may not be suitable.

Several vessels can be accommodated on a manifoldsystem allowing drying of different products at the same time, in different sized vessels, with a variety of closuresystems. Since the products and their volumes may differ, each vessel can be removed from the manifold separatelyas its drying is completed. The close proximity to the collector also creates an environment that maximizesdrying efficiency.

Batch Method. In batch drying, large numbers ofsimilar sized vessels containing like products are placed together in a tray dryer. The product is usually prefrozenon the shelf of the tray dryer. Precise control of the product temperature and the amount of heat applied tothe product during drying can be maintained. Generally all vials in the batch are treated alike during the dryingprocess, although some variation in the system can occur. Slight differences in heat input from the shelf canbe experienced in different areas. Vials located in the front portion of the shelf may be radiantly heatedthrough the clear door. These slight variations can result in small differences in residual moisture.Batch drying allows closure of all vials in a lot at the same time, under the same atmospheric conditions. Thevials can be stoppered in a vacuum, or after backfilling with inert gas. Stoppering of all vials at the same timeensures a uniform environment in each vial and uniform product stability during storage. Batch drying is used toprepare large numbers of ampules or vials of one product and is commonly used in the pharmaceutical industry.

Batch drying in a tray dryer permits precise control of product temperature and heat input.

Bulk Method. Bulk drying is generally carried out in a tray dryer like batch drying. However, the product is poured into a bulk pan and dried as a single unit.Although the product is spread throughout the entire surface area of the shelf and may be the same thicknessas product dried in vials, the lack of empty spaces within the product mass changes the rate of heat input. Theheat input is limited primarily to that provided by contact with the shelf as shown in Figure 5.Bulk drying does not lend itself to sealing of product under controlled conditions as does manifold or batchdrying. Usually the product is removed from the freeze dry system prior to closure, and then packaged in air tight containers. Bulk drying is generally reserved for stable products that are not highly sensitive to oxygen or moisture.

Figure 5

In bulk drying, heat is provided primarily through conduction from shelf. Determining Drying Endpoints

Several means can be used to determine the endpointof primary drying. The drying boundary in batch drying containers has moved to the bottom of the productcontainer and inspection reveals that no ice is visible in the product. No visible ice indicates only that drying atthe edges of the container is complete and gives no indication of the conditions in the center of the product.An electronic vacuum gauge can be used to measure condensable gases in the system. When the pressureindicated by the electronic gauge reaches the minimum pressure attainable by the system, as measured by using aMcLeod vacuum gauge or as determined previously, no more water vapor is leaving the product.As the heat input to the product is increased, evaporative cooling keeps the product temperature wellbelow the temperature of its surrounding atmosphere. When primary drying is complete, the producttemperature rises to equal the temperature of its environment. In manifold systems and tray dryers withexternal collectors, the path to the collector can be shut off with a valve and the pressure above the productmeasured with a vacuum gauge. If drying is still occurring, the pressure in the system increases.

Contamination in a Freeze Dry System

Two types of contamination can occur in a freeze drysystem. One results from freeze drying microorganisms and the other results from freeze drying corrosivematerials.

The potential for contamination of a freeze dryingsystem by microorganisms is real in any system where microorganisms are freeze dried without a protectivebarrier such as a bacteriological filter. Contamination is

most evident in batch tray dryer systems where largenumbers of vials are dried in a single chamber. Evidence for contamination can be found by sampling the surfacesof the vials, shelves and collector. The greatest degree of contamination is usually found on the vials and on thecollector. Some vial contamination can be due to a bit of sloppiness in dispensing the material originally, butcontamination on the collector is due to microorganisms traveling from the product to the collector through thevapor stream.

The potential for contamination must be consideredevery time microorganisms are freeze dried, and precautions must be taken in handling material after thefreeze dry process is completed. Recognizing that the vials are potentially contaminated, the operator shouldremove the vials to a safe area such as a laminar flow hood for decontamination. Decontamination of the freezedry system depends upon the type of freeze dry system used. Some tray dryer systems are designed fordecontamination under pressure using ethylene oxide sterilization. Ethylene oxide is considered hazardous,corrosive and detrimental to rubber components. Its use should be carefully monitored.Coupled with the risk of contamination in a freeze dry system is the risk of cross contamination when freezedrying more than one product at time. It is not a good practice to mix microbiological products in a freeze drysystem unless some type of bacteriological filter is used to prevent the microbial product from leaving thevial itself.

While freeze drying of corrosive materials does notnecessarily present a risk to the operator, it does present a risk of damaging the freeze dry system itself. Freeze drysystems are designed using materials that resist corrosion and prevent the build up of corrosive materials.But care should be taken to clean the system thoroughly following each use to protect it from damage.

Backfilling

For many freeze dried products, the most ideal systemof closure is while under vacuum. This provides an environment in which moisture and oxygen, bothdetrimental to the freeze dried material, are prevented from coming in contact with the product. In some cases,vacuum in a container may be less than ideal, especially when a syringe is used to recover the product, or whenopening the vessel results in a rush of potentially contaminating air. In these cases, backfilling the productcontainer with an inert gas such as argon or nitrogen is often beneficial. The inert gas must be ultrapure,containing no oxygen or moisture.

Backfilling of the product container is generally usefulin a batch tray dryer type system. The backfilling should also be carried out through a bacteriological filter. It isimportant that the gas flow during backfilling be slow enough to allow cooling of the gas to prevent raising thecollector temperature. Backfilling can be carried out to any desired pressure in those tray dryers that haveinternal stoppering capability, and the vials then stoppered at the desired pressure.

Stability of Freeze Dried Products

Several factors can affect the stability of freeze dried material. Two of the most important are moisture and oxygen.All freeze dried products have a small amount of moisture remaining in them termed residual moisture.The amount of moisture remaining in the material depends on the nature of the product and the length ofsecondary drying. Residual moisture can be measured by several means: chemically, chromatographically,manometrically or gravimetrically. It is expressed as a weight percentage of the total weight of the driedproduct. Residual moisture values range from <1% to 3% for most products.By their nature, freeze dried materials are hygroscopic and exposure to moisture during storage can destabilizethe product. Packaging used for freeze dried materials must be impermeable to atmospheric moisture. Storingproducts in low humidity environments can reduce the risk of degradation by exposure to moisture. Oxygen isalso detrimental to the stability of most freeze dried material so the packaging used must also beimpermeable to air.

The detrimental effects of oxygen and moisture aretemperature dependent. The higher the storage temperature, the faster a product degrades. Most freezedried products can be maintained at refrigerator temperatures, i.e. 4-8o C. Placing freeze dried products atlower temperatures extends their shelf life. The shelf life of a freeze dried product can be predicted by measuringthe rate of degradation of the product at an elevated temperature. This is called accelerated storage. Bychoosing the proper time and temperature relationships at elevated temperatures, the rate of product degradationcan be predicted at lower storage temperatures.

Contact Labconco for a complimentary catalog of Freeze Dry Systems designed for laboratory use.

The Labconco catalog, FreeZone(R) CFC-Free FreezeDry Systems -- A Complete Guide To Laboratory Lyophilization Products, provides additional informationabout freeze drying equipment and includes easy to follow selection guides. It is available upon request fromyour laboratory supply dealer or Labconco Corporation, (800) 821-5525 or (816) 333-8811.


10 Glossary Accelerated Storage: Exposure of freeze dried products toelevated temperatures to accelerate the degradation process that occurs during storage. Batch Freeze Drying: Freeze drying multiple samples of thesame product in similar sized vessels at the same time in a shelf

tray dryer. Bulk Freeze Drying: Freeze drying a large sample of a singleproduct in one vessel such as the bulk drying pans designed for

shelf tray dryers. Collapse: A phenomenon causing collapse of the structuralintegrity of a freeze dried product due to too high a temperature

at the drying front. Collapse Temperature: The temperature above which collapse occurs.

Collector: A cold trap designed to condense the water vaporflowing from a product undergoing freeze drying.

Internal Collector: A collector located in the same area as theproduct. All water vapor has a free path to the collector. External Collector: A collector located outside the productarea connected by a small port through which all water vapor must pass. Allows isolation of the product from the collectorfor drying end point determinations and easier defrosting.

Ethylene Oxide: A colorless, odorless gas used for gassterilization of tray dryer systems. Eutectics: Areas of solute concentration that freeze at a lowertemperature than the surrounding water. Eutectics can occur at several different temperatures depending on the complexity ofthe product.

Eutectic Temperature: The temperature at which all areas ofconcentrated solute are frozen. Evaporative Cooling: Cooling of a liquid at reduced pressurescaused by loss of the latent heat of evaporation. Freeze Drying: The process of drying a frozen product bycreating conditions for sublimation of ice directly to water vapor. Glass Transition Temperature: The temperature at whichcertain products go from a liquid to a vitreous solid without ice crystal formation.

Isothermal Desorption: The process of desorbing water from afreeze dried product by applying heat under vacuum. Lyophilization: The freeze drying process. Manifold Freeze Drying: A freeze drying process where eachvessel is individually attached to a manifold port resulting in a direct path to the collector for each vessel. Prefreezing: The process of cooling a product to below itseutectic temperature prior to freeze drying.

Pressure Gauge (Vacuum Gauge): An instrument used tomeasure very low pressures in a freeze drying system.

Thermocouple Gauge: A pressure gauge that measures onlythe condensable gases in the system. This gauge can be used as an indicator of drying end points. McLeod Gauge: A mercury gauge used to measure totalpressure in the system (i.e. condensable and noncondensable gases.) Primary Drying: The process of removing all unbound water that has formed ice crystals in a product undergoing freeze drying. Residual Moisture: The small amount of bound water thatremains in a freeze dried product after primary drying. Residual moisture is expressed as the weight percentage of waterremaining compared to the total weight of the dried product. The amount of residual moisture in a freeze dried product canbe reduced during secondary drying.

Secondary Drying: The process of reducing the amount ofbound water in a freeze dried product after primary drying is complete. During secondary drying, heat is applied to theproduct under very low pressures.

Shell Freezing: Freezing a product in a thin layer that coats theinside of the product container. Shell freezing is accomplished by swirling or rotating the product container in a lowtemperature bath.

Sublimation: The conversion of water from the solid state (ice)directly to the gaseous state (water vapor) without going through the liquid state. Vapor Pressure: The rate at which water moves from a solid orliquid state to the gaseous state. The vapor pressure is dependent on the temperature of the solid or liquid product.

110-98-003 5/20/98 10:47 AM Page 10


Bibliography 1. Barbaree, J.M. and A. Sanchez. 1982. Cross-contaminationduring lyophilization. Cryobiology 19:443-447. 2. Barbaree, J.M., A. Sanchez and G.N. Sanden. 1985.Problems in freeze-drying: I. Stability in glass-sealed

rubber stoppered vials. Developments in IndustrialMicrobiology 26:397-405.

3. Barbaree, J.M., A. Sanchez and G.N. Sanden. 1985. Problems in freeze-drying: II. Cross-contamination

during lyophilization. Developments in IndustrialMicrobiology 26:407-409.

4. Flink, J.M. and Knudsen, H. 1983. An Introduction toFreeze Drying. Strandberg Bogtryk/Offset, Denmark. 5. Flosdorf, E.W. 1949. Freeze-Drying. Reinhold PublishingCorporation, New York. 6. Greiff, D. 1971. Protein structure and freeze-drying: theeffects of residual moisture and gases. Cryobiology 8:145-

152. 7. Greiff, D. and W.A. Rightsel. 1965. An accelerated storagetest for predicting the stability of suspensions of measles

virus dried by sublimation in vacuum. Journal ofImmunology 94:395-400.

8. Greaves, R.I.N., J. Nagington, and T.D. Kellaway. 1963.Preservation of living cells by freezing and by drying.

Federation Proceedings 22:90-93. 9. Harris, R.J.C., Ed. 1954. Biological Applications of Freezingand Drying. Academic Press, New York.

10. Heckly, R.J. 1961. Preservation of bacteria by lyophilization.Advances in Applied Microbiology 3:1-76. 11. Heckly, R.J. 1985. Principles of preserving bacteria by freeze-drying. Developments in Industrial Microbiology

26:379-395. 12. King, C.J. 1971. Freeze-Drying of Foods. CRC Press,Cleveland.

13. May, M.C. E. Grim, R.M. Wheeler and J. West. 1982.Determination of residual moisture in freeze-dried

viral vaccines: Karl Fischer, gravimetric, andthermogravimetric methodologies. Journal of Biological Standardization 10:249-259. 14. Mellor, J.D. 1978. Fundamentals of Freeze-Drying.Academic Press, London.

15. Nail, S.L. 1980. The effect of chamber pressure on heattransfer in the freeze-drying of parental solutions.

Journal of the Parental Drug Association 34:358-368. 16. Nicholson, A.E. 1977. Predicting stability of lyophilized products. Developments in Biological

Standardization 36:69-75. 17. Parkes, A.S., and A.U. Smith, Eds. 1960. Recent Research in Freezing and Freeze-Drying. Charles C. Thomas,

Springfield. 18. Rey, L.R., Ed. 1960. Traite de Lyophilization.Hermann, Paris.

19. Rey, L.R., Ed. 1964. Aspects Theorique et Industriels de laLyophilisation. Hermann, Paris. 20. Rowe, T.W.G. 1970. Freeze-drying of biological materials:some physical and engineering aspects. Current Trends in Cryobiology: 61-138. 21. Seligman, E.B. and J.F. Farber. 1971. Freeze-drying andresidual moisture. Cryobiology 8:138-144.

11

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Labconco Corporation8811 Prospect Avenue Kansas City, Missouri 64132-2696816-333-8811, 800-821-5525 FAX: 816-363-0130, E-Mail: labconco@labconco.comHome Page: http://www.labconco.com (C) 1998 by Labconco Corporation Printed in the U.S.A. 3-53-5/98-BH-5M-R5

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InvisibleWakingUpLate
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Re: drying problems-freeze drying? [Re: Anno]
    #592830 - 03/29/02 02:50 PM (15 years, 4 months ago)

Thanks Anno, i'm printing it so I can sit and read it (my monitor's
giving me a headache)
So what's your opinion of drying under extreme vaccum at
room temp? Would it be a waste of time to build a metal
vaccum chamber or do I just need to try it and see.
And what about drying prints this way, would the spores
explode?
I'm really curious about all of this. (as you can see)
Thanks again. :peace:

Free Spore Ring 


--------------------
The rest of those, who have gone before us,
cannot settle the unrest of those who follow.
(Finding Forrester)


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OfflineSeussA
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Re: drying problems-freeze drying? [Re: WakingUpLate]
    #592834 - 03/29/02 02:57 PM (15 years, 4 months ago)

You can pick up a vacuum dessicator (plastic) on labx auction for under $20 US. There are usually a few of them running at any given time. The glass ones are a bit more expensive, but not really needed since you wont be using any solvents.


--------------------
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Re: drying problems-freeze drying? [Re: GaNjAShRooM]
    #592856 - 03/29/02 03:21 PM (15 years, 4 months ago)

For a lot, lot, lot cheaper method, I suggest Damp Rid dessicant (home depot $2-3 per half gallon container).
It kicks ass. your shrooms will be completely 'stem snapable' dry in less than 48 hrs. There is plenty of info on procedures and setups for this method on this site. Basically, get a plastic tub w/ lid, then pour a thin layer of damp rid (half inch is good) on the bottom, then get some hardware cloth or any kind of wire mesh and make a rack inside your bin for the shrooms to sit on (don't let them touch the dessicant). Finally, put your lid on the bin and wait about a day and a half!!!! It's okay if your lid isn't air tight, I used to duct tape the edges of my lid shut and it took longer than my friends set-up who didn't seal his bin. simple and very effective. Damp rid can also be dried out in a oven for re-use.


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InvisibleWakingUpLate
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Re: drying problems-freeze drying? [Re: KerPluNk]
    #592870 - 03/29/02 03:45 PM (15 years, 4 months ago)

Dessicant is a given, that we are all aware of.
The focus of this thread is alternative drying methods
for mainly aesthetic reasons. :peace:

Free Spore Ring
Seuss, thanks I'll check those out.


--------------------
The rest of those, who have gone before us,
cannot settle the unrest of those who follow.
(Finding Forrester)


Edited by WakingUpLate (03/29/02 03:52 PM)


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OfflineMichiaelJackson
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Re: drying problems-freeze drying? [Re: WakingUpLate]
    #10581214 - 06/27/09 01:07 PM (8 years, 1 month ago)

Not meaning to bring up a 6 yr old thread, but this is something that I am interested in.

I am concerned with freeze drying, as it is very difficult to form amorphous ice without some really really high tech equipment, and may be impossible in the mass of that which would be contained in a fruit. As best as I can tell, the easiest (only?) way to make amorphous ice is to have water at an extreme vacuo and have it condense on something very very cold (-137C or colder). This would prevent amorphous ice from ever happening within a fruit.

as matter heats it expands and as it cools it contracts. This is included within phase changes. In the case of crystalline solids, the change from liquid to solid can reduce its overall density do to the formation of crystals. Also, as a crystalline solid forms (ice) within a fruit body, it tends to poke holes in cell walls/membranes. In more fibrous tissues, this isn't necessarily horrible but in the world of fungi you end up with a nice goo.

I guess my main point is, why bother freeze drying? the process of freeze drying requires the water to become a solid (freezing) then to be placed in a vacuo to cause the ice to sublimate into a gas. I'm concerned that allowing the ice to crystallize with cause the damage, regardless of what process(es) are preformed afterwards.

By using the chart below (retrieved from http://b.colonizingvenus.org/Phasediagram_Water_Planets.gif) I see no need to place the fruits into a condition where ice is able to form.


(Sorry about the poor quality, I had to scale it down slightly to get it to upload, I was over by 1 byte, doh!)

My main arguments against freeze drying:
1. Freezing causes ice. Ice may cause tissue damage.
2. The more heat that is removed from the system, the higher the level of vacuum that must be achieved in order to transition water into a gas (this can mean more expensive vacuum devices)
3. Energy is required to cool the system, therefore reducing the drying power to energy expenditure ratio. Point 2 also will require more energy, therefore reducing that ratio further.

My main arguments for vacuum drying:
1. Desiccants are gross and disposable, which can cause problems.
  a. In a commercial growing operation of dried mushrooms (Shiitake for example), the total cost of energy for vacuum drying vs. desiccants has to be investigated. While vacuum drying will undoubtedly have a higher start up cost, if it has a lower reoccurring cost, it will pay for itself in the long run.
  b. Disposal of desiccants can be expensive in the long run, as well as possibly environmently unsound. Reusable desiccants are possible, however they have a higher energy cost to dry (which may or may not be cheaper than replacing it).
  c. In organic farming, there are many restrictions as to what can come into contact/proximity to edible foodstuffs. Some desiccants may be forbidden through the regulatory agencies that certify an organic farm. Even if allowed, a vacuum drying process will leave many fewer questions than any sort of hygroscopic substance.
  d. for the commercial farmer, regardless of organic certification status, may not want to have the chance of containments coming in contact with edible foodstuffs. Some times the only way to win is to not play.
2. Large batches can be done at once, as vacuum pumps are rated by maximum CFM and maximum vacuum to be able to maintain; the volume of the container is insignifigant (larger containers may be beneficial, depending on the rate of vacuum).
3. Floor footprint isn't as crucial, allowing for diverse configurations. Desiccants work on surface area (much like using perlite as humidifier), making optimal conditions using a shallow container with a large footprint. A vertical configuration is plausible with a vacuum drying system, while using a desiccant in such a configuration may cause a lack of time efficiency.

The one consideration for container size (as briefly mentioned above) is that when changing the mass within a container, you also change its temperature. This is easily noticed when using a can of 'dust off' or other aerosol, the can becomes cold while depressurizing (which is the same effect as placing a vacuum on a container). This heat exchange has numerous factors, including surface area of the container, thermal conductivity of the container surrounding air and contents, and rate of pressure change. While I am sure I could figure all this out on a case-by-case basis, I won't even attempt to create a formula to figure this out.

That being said, a slower vacuum will cool slower or at least reach a thermal transfer equilibrium easier. The larger the volume of the container, the stronger (faster) of a vacuum you will need to get it to cool off tremendously. Some heat may need to be applied (or a vacuum speed regulation) to ensure that the water does not have the opportunity to freeze at any point.

So, for anyone who has had the patience of a patron saint to read all of this drivel, does vacuum drying (at least in a commercial sense) seem like a viable method?


--------------------
Wanna hear something depressing? One out of four Shroomerites wants to lock me in a government cage for using a substance they don't like.

Hard to believe, right? Read it for yourself:

http://www.shroomery.org/forums/showflat.php/Number/7874721#Post7874721


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Invisible13shroomsM
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Re: drying problems-freeze drying? [Re: MichiaelJackson]
    #10581260 - 06/27/09 01:29 PM (8 years, 1 month ago)

Quote:

So, for anyone who has had the patience of a patron saint to read all of this drivel, does vacuum drying (at least in a commercial sense) seem like a viable method?




unless your drying hundreds of lbs, no, IMO dehydrators (baught/home built) work best and most consistantly.


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OfflineMichiaelJackson
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Re: drying problems-freeze drying? [Re: 13shrooms]
    #10581427 - 06/27/09 02:31 PM (8 years, 1 month ago)

Quote:

13shrooms said:

unless your drying hundreds of lbs, no, IMO dehydrators (baught/home built) work best and most consistantly.




For the home grower, it would be for novelty purposes only.

Do you think that it would be an effective treatment for a commercial application?


--------------------
Wanna hear something depressing? One out of four Shroomerites wants to lock me in a government cage for using a substance they don't like.

Hard to believe, right? Read it for yourself:

http://www.shroomery.org/forums/showflat.php/Number/7874721#Post7874721


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InvisibleJaComet
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Registered: 11/12/02
Posts: 347
Loc: Out Yonder
Re: drying problems-freeze drying? [Re: hispeed67]
    #10581994 - 06/27/09 05:28 PM (8 years, 1 month ago)

Quote:

hispeed67 said:
How does one do freeze drying???




Here ya go.  How To Freezer Dry at home with a frost free refrigerator freezer:

http://www.shroomery.org/forums/showflat.php/Number/1264202#1264202


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Offlinemuppyvw
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Re: drying problems-freeze drying? [Re: GaNjAShRooM]
    #22466636 - 11/02/15 03:16 PM (1 year, 9 months ago)

[image][/image]I'm new to the game.
Went picking yesterday and thought I could put my mushrooms in the oven(so that they were away from the cat).
It wasn't until I checked on them later that I realized the oven was slightly turned on.

The steam looks crunchy and the cap is black/ and mostly dried.


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Invisible13shroomsM
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Re: drying problems-freeze drying? [Re: muppyvw]
    #22466661 - 11/02/15 03:25 PM (1 year, 9 months ago)

dude look at the time stamps b4 you bump anymore 13yr old threads  :waits:


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Offlinemuppyvw
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Re: drying problems-freeze drying? [Re: 13shrooms]
    #22466740 - 11/02/15 03:54 PM (1 year, 9 months ago)

Sorry. I'm new to this site. Literally signed up today. I was very nervous and wanted advice. In terms of rules and etiquette for this group I'm still sorting that out. Could you explain what I did wrong? I wasn't able to completely understand your statement.

Plus, I'd still like some advice to my previous question. Where would be the proper place to do that?


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